AC Ace and Aceca Lucas wiring diagrams
There is no electrical section in the workshop manual. These Lucas diagrams cover the Ace as well as the Aceca. The copies are held by the owners club, and four diagram numbers are recorded.
The four Lucas diagram numbers
These numbers come from the AC Owners Club forum rather than from a published parts list, which is why the archive treats them as the best available record rather than as factory gospel. They are period specific, so the right one for a car depends on its chassis number and build date.
| Lucas number | Document title | Date | Covers | Notes |
|---|---|---|---|---|
| W29340 | Not recorded | April 1955 | 1955 | The earliest found. Shows a single speed wiper. |
| W29340A | Lucas Electrical Equipment A.C. 'Ace' Sports Cars (1955-57) Home and Export Models | March 1957 | 1955 to 1957 | Supersedes W29340. Carries the instruction that the earlier diagram 'should be destroyed'. |
| W31520 | Not recorded | April 1956 | 1956 | Superseded by W31520A. |
| W31520A | Wiring Diagram for 1956/1957 Ace Home & Export Models | February 1957 | 1956 and 1957 Home and Export models | Supersedes W31520. Described on the club forum as an Ace diagram, while a copy offered for sale was described as an Aceca diagram. One diagram may cover both, but the archive does not assert that. |
Where to get a copy
The diagrams are obtainable through the AC Owners Club archives and library, and through the members' area. Within the club members' area, the diagrams sit under Model Directory, then Ace, then Articles, under a heading that reads Wiring Program rather than Wiring Diagram. Two documents are held there. One is the 1955 to 1957 diagram. The second carries no header and is believed to be for a 1957 car with the AC engine, though the club's own note says its origin is uncertain. The club archive and library hold more, and members in the thread have enlarged and posted A3 copies to owners who asked. A3 matters: these are photocopies of photocopies and the small print does not survive reduction to A4.
The practical advice from members is to ask on the club forum quoting your chassis number, because the diagrams are period specific.
Autosparks, who manufacture replacement harnesses, supply no fitting instructions or diagrams with the loom. That is not a criticism of the harness; it is simply why the club archive matters.
What the archive could not establish
Whether W31520A is strictly an Ace diagram, an Aceca diagram, or a single drawing that covers both body styles. The club forum and a commercial copy give different descriptions. Either could be true, but the archive has not seen evidence that settles it.
Both suffix A diagrams are titled for the Ace by the members who hold them, W29340A explicitly as "A.C. Ace Sports Cars". Against that, a Lucas parts reference for AC Cars, CE852/63, covers the Ace Sports, the Aceca Coupe, the Greyhound GT Saloon and the Cobra in one document, so Lucas did not always separate the models. The archive records both and settles neither.
Note what the titles do not cover. W29340A covers 1955 to 1957 and W31520A covers 1956 and 1957. Neither claims to cover a car built in 1958 or later, and no member in the thread produced a diagram issued after February 1957. An owner of a later car should ask the club which diagram applies rather than assuming the latest number listed here.
The archive also could not confirm whether additional numbers exist for export-only equipment or for cars fitted with an alternator later in life.
Where the diagram and the car disagree
One member reports that his car's horn push controls a horn relay, supplying the horn circuit through it, while the diagram shows the horn push supplying an earth directly. The relay is a Lucas 6RA, listed in the Lucas parts reference for AC Cars as part number 33188B.
Other cars do not match it. Photographs of one car published online show no relay, and another car that left the works in July 1954 was found to have none. The April 1955 diagram, W29340, shows the horn wiring without a relay.
A member asked at which car number the relay arrangement changed and nobody answered. One member observed that a relay is the better arrangement, since without it the full horn current passes through the push, and that later Acecas carry horn and overdrive relays, which makes a deletion seem unlikely. The archive cannot establish what happened, only that at least one car does not match its diagram.
The wider point stands for anyone rewiring. Members note that these were hand built cars, that components migrated around the engine bay as production went on, one example being the indicator and lights relay moving to the front wheel arch, and that body details differed between cars built within months of each other. The diagram is the starting point, not the final word. Check your own car.
Related reading
- The wiring loomWho makes replacement harnesses, the Lucas colour code and the earthing problem.
- Positive earthWhat the polarity means for battery, coil, dynamo and accessories.
- The Lucas control boxWhat the RB106 does and its commonest fault.
- Horn and indicator wiringThe stator tube, the Lucas switch and how to thread it.
- Clubs, registers and recordsWhere the factory records live and how to reach the club archives.
- Parts and specialistsWho supplies parts and who works on these cars.
The archive holds no copy of any of these diagrams and does not reproduce them. They belong to the club archive, and that is where to ask for them. The document titles, issue dates and the horn relay discrepancy are drawn from a thread on the AC Owners Club forum running from September 2018 to January 2022, in which members quote the diagrams they hold.
If a diagram number is wrong or missing, or if you know of a better source, please get in touch.
About the author
A lifelong classic-car enthusiast in North Yorkshire, near Thornton-le-Dale, who owns and maintains an AC Aceca, writing the single-model reference he always wished existed. Read the full bio.