of AC's post-war 2 Litre Saloon


Old British electrics have a poor reputation, yet I rarely encounter any examples of failures other than when parts have been neglected, abused or not used for a long period. Some criticism comes from idiots who had broken the parts in the first place! The only electrical failure on my AC, was the non-working Smiths clock when my Dad ran the car. I fixed it later.

If problems do occur, the most likely culprit is the wiring, due to neglect, poor connections when last wired up, or because it's extremely old.

The 13 amp generator might be considered marginal, if accessories are used altogether, or if more electrical equipment is added. It is possible to do a conversion to an alternator, disguised as the generator. You can also get electronic control-boxes for improved charging (with a generator retained). And you can consider LEDs to lower the current demand, assuming that these are legal where you are?


I've seen 4 versions of AC's schematic diagram, and none match my 1949 AC's original wiring! There were numerous detail variations, but only two major changes that I know of, that occured almost at the same time (around 1951/2). At the time of writing (2020), Autosparks in the UK sell two versions of the harness.

The earlier ACs had no horn relay, and employed an RF95/2 control-box which incorporates two fuses. They also had no earth wires for the side lamps. From about 1952, the RB106/1 control-box was used, and a separate fuse-box. The schematic in the Series 2 handbook, shows the earlier control-box, but also a horn-relay, so the changes must have happened at different times. It also shows an additional fuse for the side/tale lamps. So, check your wiring in detail before ordering a new harness, as you might have to have one custom made?

Note that the earlier ACs had no fuse for the side, tale, interior and head lamps. 1 of the 2 fuses is just for the horns, while the other fuse covers certain items that can operate when the ignition is turned on. I.e. Brake lamps, wipers, trafficators and fuel gauge.

The earlier schematics show some details that I've not come across, but presumably apply to very early cars. These include under-bonnet lamps, twin interior lights (rather than one) and a single numberplate lamp (rather than two). Also, a battery master-switch, which might be a wise addition to a classic car as a precaution against fire during storage?

Don't forget that it has positive earth.


The original wiring had rubber insulation under cotton-braid colour coding. New replacement harnesses have PVC insulation under the cotton-braid. There are bullet type connectors used under the wings. They are also found under the front floor and rear seat (left-hand side). I would recommend smearing the contact surfaces with petrolium-jelly (vaseline) which will prevent corrosion and maintain contact, plus making it easy to dismantle later. The contact surfaces should be cleaned up first if necessary. I know that seems counter intuitive (and there's lots of rubbish online about this topic!), but it conducts when in a tight fitting joint, as well as keeping out air and moisture. I've used it. It works.

Some wires are fastened to the wood frame with insulated staples. Eventually, the insulation crumbles away and the steel staple might dig into the wires. These staples are used for the trafficators and interior light, and can be accessed after removing the rear seat, side trim, and the aluminium panel under the seat.

Being a wood framed car, there are a lot of earth wires. Earth wires from the harness connect to the aluminium bulkhead and to the aluminium frame under the rear seat. The petrol tank is earthed through that rear frame via its bolts, but I plan to add an extra earth lead from one of the fuel-gauge sender screws to the aluminium frame. I've changed those sender unit screws to brass ones (rather than steel).

For information on routing a new wiring harness, see further down this page.


Most AC 2 Litres had trafficator model SF34N originally, with model SF80 fitted from 1953 onwards. A lot of the earlier ACs have since had them replaced with the SF80 model which is the familiar type seen on many British classics. SF34N had a different shaped arm and a different shade of orange. The main technical difference is that the lamp is supplied via a wire that bends as the arm raises and lowers. On SF80, the lamp connects via moving contacts. Also, on the SF80, it is possible to replace a damaged arm without removing the whole unit from the car.

The contacts on the SF80 trafficator work well since they are sliding contacts that self-clean. If the arm is reluctant to raise, especially when warm, it probably means there is dirt on the plunger. With the unit removed from the car, you can clean up the mechanism (especially the plunger) with meths or some other alcohol based cleaner, with a cotton-bud. It is important that the plunger stays dry and clean, and no oil or grease gets onto it. When it gets hot, any dirt on the plunger might become sticky. Any oil on it will attract dirt.

There is a locking mechanism that stops the arm swinging outwards when closed. Don't pull the arm out against this lock, otherwise it will eventually wear or break. With the rest of the mechanism cleaned, you can apply a tiny bit of grease to the back of the locking mechanism. The only regular lubrication is for the arm's pivot. A tiny drop of oil at each end. This can be done with the trafficator on the car, by using a small screwdriver with a single drop of oil on its tip. Keep the oil away from the electrical contacts. I would oil it maybe once or twice a year, depending on how much use the car gets.

The original SF34N type, has a lubricating pad inside the arm to which one drop of light oil can be added. Access to this requires the top cover of the arm being removed.

If it has been neglected, then the pivot might wear to the point of breaking. This pivot is a rivet, so to remove it you have to destroy it by filing off the head. You can replace it with a steel screw and nut, provided that the nut is secured/locked on.

To access the festoon bulb, remove the tiny screw at the tip of the arm, and remove the stainless steel top cover. This cover provides the earth for this 36mm bulb. Electrical problems are unlikely except in the supply wires. The earth wires are very short leads that connect onto the aluminium frame behind the rear seat.

My trafficators draw just under 2 amps current, which I believe is about right. Note that they will not over-heat if the arm sticks. In fact, current draw is less when it is stuck closed. The force from the solenoid increases as the plunger moves into it, which relates to the increasing load from the arm as it opens.

They are mounted on adaptor plates to make them flush with the body. This part was missing from one of my trafficators, so I fabricated one. I also made a new rubber stop.

And here is a fun (technical) fact: The SF80 version has the metal arm cover shaped aerodynamically, to help the arm close when the car is travelling fast.

Wiper motor

Up until 1951, ACs used the CR1 type of motor, with a control knob on the dashboard giving manual control, and allowing wipers to park off the screen. Then motor types CR4 and then CRT14 were introduced, and these are controlled by a switch. CRT14 has a thermo cut-out. Don't worry that there's no cut-out on the earlier models. The stalling current is low enough not to cause damage (assuming everything is in good order). In the model names, C=cable, R=rack and T=thermostat. I have read that thermo cut-outs can cause problems such as cutting out at too low a temperature. If you are not bothered about originality, you can always upgrade to later, faster wiper systems?

Wiper problems are more likely to be external to the motor, either wiring or the wiper mechanism. A potential problem with the motor gearbox, is the grease packed inside. The original grease was a special type, which unfortunately goes hard and dry after a few years. When I checked mine (back in the 1980s), it was pale yellow and was like a crumbly cheese. That original grease (Duckham's Keenol KG25) is no longer available, and many people use a white lithium grease instead. It is important not to use a grease which conducts electricity (so, no metal dust in it), and one that has a wide operating range of temperatures including sub-zero. You will need to remove as much as possible of the old grease, before repacking it with fresh grease, as you don't want a mix of types. I removed the large gear to help with the grease change. Remove the small cover under the gearbox, and then there is a split-pin securing the gear spindle.

The rack and wheelboxes use a small amount of light oil for lubrication.

If you remove the motor's plastic end cover, you can check to see if new brushes are needed. The ones in the photo on mine, are probably the originals still going strong after 100,000 miles (in the UK climate!). While the motor is apart, you can check and clean the commutator. Scrape out any carbon built up in the slots between each copper segment. Mine required almost no attention other than a light clean. If necessary, the commutator can be cleaned with very fine abrasive paper, such as 1,000 grit. Ideally, have the abrasive fixed to a solid strip, rest it against the commutator, and spin the armature to make sure all the segments get an equal amount of cleaning (uneven commutators cause more sparking). Clean afterwards with alcohol based cleaner used sparingly.

In the photo above, you can also see the thrust ball on the end of the shaft which takes the end thrust from the worm drive. In the end cover, you can see the self-aligning bearing. There is an adjustment screw outside the end cover, with a lock-nut. If adjustment has been lost, then it should be set so that there is just enough end-float to allow the armature to rotate.

The motor sits upon 3 circular rubber pads, glued on, but these can come adrift. Many owners add a strap, and a stainless strap had been added to mine. I added some foam neoprene padding onto the strap, to insulate motor noise.

For testing the wiper system, the motor should draw between 1.75 and 3 amps when cold (wet screen). It should give between 90 and 100 wipes per minute. At least that's what the Lucas publications say! My motor tested at about 60 strokes per minute on the bench, drawing 1.5 amps, with fresh grease applied. My wipers were always terribly slow!


Most ACs have either the RF95/2 or RB106/1 control boxes, but they are similar internally. They have 2 solenoids to deal with voltage regulation and a cut-out to prevent current flow into the generator. If it has been out of use for a long time, then it is worth checking that the contacts are clean and the armatures move freely. Also, that the terminal connections are in good condition. If it is damaged beyond easy repair, then be careful to obtain the exact same model when seeking a replacement. There are different versions of each model. The model RF95/2 on the AC, is part number 37065E. Lucas quote the RF96/2 (no fuses incorporated) being fitted to later ACs, with part number 37048E. I wonder if this was fitted to a few ACs before RB106/1 (part number 37174) became standard?

The 2 fuses are rated at 35 amps instantaneous.

To connect up the RF95 (9 terminals) to the wiring harness, working from left to right: Terminal A1 connects to the ignition switch terminal A (brown with blue); terminal A connects to the ammeter terminal A (brown with white); terminal A2 connects to the horns (purple); F goes to the generator field windings terminal F (yellow with green); D goes to the generator terminal D and the ignition light (yellow leads); there are two terminals labelled A4, connected to each other, and go to several items (fuel gauge, fog lamp, wiper motor, brake lamp switch, indicator switch) all green leads; E goes to earth and the earth lead to the dashboard (black); A3 goes to the coil (SW) and the IG terminal of the ignition switch (both white leads).

For the RB106/1 with 5 terminals, follow the above connections for A1, A, F, D and E.


These are unlikely to give trouble unless you've rescued a pair that have been outside for a long period. The contacts might need cleaning if they have been out of use for a long time. If the horns sound, but sound bad, then they are probably not bolted down securely. It might be the mounting board that is loose? They need a very rigid mounting, to produce a good sound. If you renew the wiring, make sure that they can handle the large current drawn by horns, 6 amps for each one. The original wires are 14 strand, rated at 7 amps (8.75 amps for modern leads), although I think they are a bit close to their limit. It might be wise to go up to 28 strand, to be safe? While all electrical connections on the car should be done well, it is even more important with high current items such as horns. All terminal surfaces should be clean and free of corrosion, and then smeared with a tiny bit of vaseline to maintain good contacts.

Be careful that the single long screw holding down the dome cover, does not touch the contacts. I inadvertently swapped the screws between my 2 horns, and it shorted out. I cut the longer screw to avoid making the same mistake.

If they have had a lot of use, the contacts might be worn and need re-adjusting. They should be adjusted so that each horn draws the correct 6 amps of current, from a battery giving 12 volts when not under load. I.e. A good fully charged battery.


Jay Leno likes to wind up (terrible pun!) us Brits over the Smiths clocks that are accurate twice a day. I don't get ticked (oops, another one!) off, since I like Jay. The electric clock on my AC did not work while my Dad ran the car. I then fixed it quite easily and it was still working 8 years later when the car ceased running.

The escapement in this clock consists of a disc which turns through a small angle, to and fro against a spring. There is a short, fine wire sticking out of the side of this disc. As the wire moves with the disc, it makes and breaks contact with a delicate brush. The fine piece of wire on mine, had eroded away where it made contact with the brush, until it ceased to touch. So, I tinned it with solder, using a fine soldering iron suitable for electronic work. Much to my surprise, this solder has not worn away so far.

Brake-light switch

The contacts slide across each other, so they are self-cleaning. It is possible for the contacts to bend permanently if the switch has been pulled too hard, such as if the wrong type of tension spring has been fitted. So make sure that they close properly and that the tension spring does not pull too firmly.

Horn/indicator switch

You might regret dismantling this switch! There are a number of springs inside, and parts can fly out. Place it inside a container, or clear bag, before opening it.

To remove the assembly from the steering column, you have to undo the compression nut at the bottom of the steering-box, and remove the olive. You'll need to catch the oil that will drain out. With the leads disconnected, slacken the grub-screws on the sides of the steering wheel boss. Then you can pull the assembly out - the cable tube being in 2 sections.

Unscrew the metal flange from the back of the unit, and the upper tube will come away. Then the metal ring around the switch will pull off. Don't drop the 2 brass fingers for the self-cancelling mechanism. You can remove the screws holding the front cover on, being careful as there is a spring under the horn button. Then remove the plastic section with the terminals. Now it should look like the photo above. The indicator lever at the top, has 2 return springs that had worn out on mine, but that is easy to fix. Nothing else is likely to have worn out. I cleaned mine and smeared a tiny bit of silicone grease on the self-cancelling fingers. Check that the self-cancelling functions correctly as you reassemble. The 2 self-cancelling fingers must be placed in the correct way round, as in the photo.


There is nothing much to say about light maintenance, other than checking the condition of the bulb holders and using the correct bulbs and supply leads. The longer the lead, the more important to have it large enough in section.

The early headlamp lenses, with a cats-eye design, is not effective in directing the beam. It tends to send some light upwards, so that you dazzle on-coming traffic when driving down a dip in the road. These lenses were superceded by a more modern block lense design. If you use your AC much, then it might be worth upgrading.

The later side/tail lamps (Lucas L488), are readily available if you need replacements. The earlier L461 type (mounted on a tubular projection from the wings) is much harder to find. Some of them, as used by other makes, have different lenses to the flat ones seen on the AC. There have been some reproduction ones made over the years.

Routing the wiring harness

The main harness runs inside the left-hand chassis rail. Along the open channel section of the chassis, there are 3 chassis clips to secure the cable. In the engine bay, the cable emerges just behind the left-hand steering-box mounting, and is secured by an aluminium P-clip. There is a heavy-duty plastic sleeve to stop the cable chafing on the chassis cross-member. Then it runs up the inner-wing, clipped to one of the louvres with a chassis clip, and then to a junction-box.

Also connected to the rear of that junction-box, are wires to the steering column (indicator and horn switches). These are held to the brake pipe with aluminium cable-ties.

Another large cable attaches to the front of the junction-box and passes through a gap (bottom left of radiator) into the radiator cowl. It leads to the front lights and horns. Wires for the lights pass through the inner-wings (through grommets), to bullet connectors. Wires to the lights are held by chassis clips to the side rails. The cable to the horns is also held by a chassis clip to the mounting bracket.

Moving back to the bulkhead, a cable branches off the harness out of the chassis (again, sleeved for protection) and up the edge of the bulkhead, held by a pair of aluminium P-clips. 2 more P-clips hold the cable under the control-box, if you have the earlier combined control-box with 2 fuses. A wire branches off for the ignition coil. Then 2 wires for the wiper-motor. The cable continues to the dashboard (another P-clip), through the bulkhead (with a grommet). Inside the car, carpet trim on the plywood bulkhead covers some of the cable which is secured by another P-clip. Don't forget the earth wire for the fuel pump. Most important! You can earth it to the bulkhead. The bulkhead itself is earthed by a wire on the main harness with a large eye connector, and this goes onto one of the coil mounting bolts.

For later ACs with a high mounted fuel filter, the main cable passes behind the wiper motor.

A pair of wires run from the control-box back down the bulkhead, and then cross the bulkhead to the dynamo, secured with smaller steel P-clips.

Under the front floor, wires branch off the harness with bullet connectors. They connect to a cable for the headlamp dipper switch and the brake light switch. That cable is secured with a pair of aluminium cable-ties to the sling under the bell-housing. Be careful that this cable doesn't hang too low and risk getting damaged.

Moving further back, another branch comes off under the rear seat, again with bullet connectors. These link to the trafficators and interior lamp. There is also an earth wire for the aluminium frame under the seat. This is fixed by one of the little screws and nuts for the frame assembly. The wire for the right-hand trafficator, is held against the tubular chassis cross-member with 3 aluminium cable-ties. It is then held to the wood frame with insulated staples and passes through small holes in the woodwork. Near the trafficator, it is stapled to a slight recess. The left-hand trafficator lead is similar except that it is accompanied by a pair of wires for the interior light. These interior light wires continue up on top of the cantrail, through small holes and transversely across the roof with more staples to hold it. The trafficators have short earth leads that go to screws holding the alumninium frame behind the seat back-rest.

Further back, a single lead comes off the harness for the fuel gauge sender. It passes under the leaf-spring, over the underpan, and up behind the fuel tank. It has an extra layer of insulation for safety.

A little further back, and the last 2 wires emerge and pass over the rear cross-member and out under the inner wing. These wires are for the tail and brake lamps. They have double bullet connectors (under the left-hand rear wing) to link to both sets of rear lamps plus the numberplate lamps. There is an earth wire screwed to the left-hand inner wing, again with a double connector to link to all the rear lamps. The leads for the right-hand lamps are secured by an aluminium P-clip to the left-hand inner-wing.

Leads to the rear lamps are protected with heavy duty plastic sleeving under each wing. Wires to the right-hand lamps run along the front edge of the rear wooden cross-member, secured with 3 steel P-clips. The leads to the number-plate, pass through a hole in the steel floor (with a grommet), and then along the top of the door. It is held by steel P-clips and staples, which seems like over-kill!

Most of the wires are 14 strand, originally rated at 7 amps. 28 strand leads (14 amp original rating) are used for the following items:

- Dipper-switch to front junction box.
- Horn switch to the junction box (for non horn relay early ACs). For later ACs, I presume 28 strand is used from the relay to the front junction box and to the relay from the starter-solenoid?
- Low tension leads for coil and distributor.
- Fuel pump.
- Cold start solenoid.
- Control-box A1 to ammeter.
- Control-box A to ignition switch.
- Control-box A2 to front junction-box (horns).
- Control-box D to dynamo.
- Control-box A4 to wiper motor.
- Control-box A4 to front junction box (indicator switch).
- Control-box E, 2 wires, 1 to bulkhead earth and 1 to dashboard earth.
- Control-box A3 to coil.
- Ammeter B terminal to starter solenoid.

The modern equivalent wires have slightly higher current ratings. Panel lamp wires can be just 9 strand (4 amp).

Additional individual wires under the bonnet, include those from the coil (actually taking power supply when ignition is on) to the fuel pump and the cold-start solenoid (white leads). Another wire from that solenoid to the thermostat (white with black), and then the earth wire from the thermostat to an inner wing small bolt (earth wires are black). Most importantly, an earth wire for the fuel pump to the bulkhead and the earth strap from the engine (sump bolt) to the chassis (right-hand side of cross-member).

There is additional wiring behind the dashboard. The 2 wires (red with white) for the lamps on the 2 dials, go to one side of the panel light switch. The other side of that switch is connected to the T terminal of the ignition switch (red lead). The lead (brown) to the clock, goes to the B terminal of the ammeter. Two white leads connect from the IG terminal of the ignition switch to the ignition lamp and starter push-button respectively.

At least, that is what the schematics show! My AC was different, so that the panel lights could be switched on without the side lamps being on, and also so that the starter push works without the ignition turned on. Mine had the clock lead going to the starter push button. And from that same starter terminal, a lead went to the panel light switch. From the same panel light switch terminal, another lead went to the B terminal of the ammeter.

More colour codes:

Tail, side and number-plate leads are red.

Brake light leads are green with purple.

Right-hand trafficator lead is green with white,

Left-hand trafficator lead is green with red,

Headlamp main beam leads are blue with white.

Headlamp dipped beam leads are blue with red.

For early non horn-relay ACs: Horn leads from the A2 fuse are purple. Horn leads to push-button are purple with black.

For later ACs with a horn relay: Horn leads from relay are brown with green (horns have earth leads - black). Lead from relay to push-button is brown with black. Lead to relay from fuse is green.

Leads from fuse (A4 fuse on the early 2 fuse system) to wiper-motor, brake light switch, fuel gauge, trafficator switch and fog-lamp switch, are green. Also a green lead to horn relay on later cars.

Fuel gauge sender lead is green with black.

Fog-lamp lead is green with blue.

Dipper switch from light switch lead is blue.

Ammeter B terminal to starter solenoid (battery supply terminal) lead is brown.

Starter button to starter solenoid (small terminal) lead, is white with red.

Wire terminals:

Most terminals are bare wires into screw terminals, or bullet type push-in connectors. The exceptions are the following:

Slotted Y-shaped terminals (3/16") for the dipper switch and dynamo F terminal.
Slotted Y-shaped terminal (1/4") for dynamo D terminal.
Eyelet terminal (3/16") for earth leads on numberplate light (left-hand), fuel pump, front lights, rear lights and trafficators. Also for fuel pump supply lead, leads on coil and cold start solenoid.
Eyelet terminal (3/8") for bulkhead earth and starter solenoid (from battery).
Eyelet terminal (5/16") for starter solenoid (to starter motor).
Eyelet terminal (1/8") for fuel gauge, fuel gauge sender and wiper switch earth.
Flag type eyelet (3/8") for engine earth strap, both ends, and for battery earth (onto dynamo bolt).
Flag type eyelet (3/16") for ignition light.
Bullet sleeve connectors for trafficators and right-hand numberplate light earth.
The numberplate supply leads have terminal ends shaped like a hollow nail, that can't be pulled out. The wires have to be threaded through the lamp sockets and then soldered onto the terminals. Lucas part number 188156.

Number-plate light assembly.

Some additions one might want to consider - for safety - might be battery isolation switch, fuses for lights, and extra earth wires? Any extra electricals, such as a fan, should have its own fuse added.

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Website started 29th December 2006