Firstly, confused about white/purple wire coming from Cutout unit terminal A to ignition switch. There is also a white/purple from ammeter to ignition switch... But where does it come in to?? Inference says both into terminal A... But it seems wrong.

Does it matter which side of the ammeter the purple/white goes into?

Secondly, which Starter unit bolt do I attach the neg earth wire to, or do I assume that it is already well earthed to block, and just make a body-engine strap? (To anywhere on bulkhead presumably, for an otherwise alloy car?)

These colours are all from Ruby diagrams.

Here's a wiring diagram to support the question.

http://www.austin7.org/Technical%20Articles/PLC%20Switch%201/

the diagram in the link shows 2 'A' terminals, joined by a dotted line, your Ruby diagram shows a line inside the switch from one marked A to your unmarked one. I'd say that you're right.

Where does your battery earth attach?

Location: Oxfordshire

Thanks. My battery earth is to corner of engine.


Looking at the CASC page, it does seem to suggest that it would be just another source of earthing on the other side of the unit. I have all the other terminals, just not that 2nd "central" one.

Do other people have 'that' inner stud accessible? (with a wider entrance for wires narrowing to the terminal grub screw - or rather lack of it!... mine which has a dummy stud.)

Life would have been so much easier for many if Austins, Pitmans, Woodrow etc had published a similar drawing. It is difficult to sort non standard arrangements or to fault trace from the Austin diagrams. Even for those with electrical experience, it takes some thought to fathom the workings. It would be worthwhile for the non tech to keep a diag in the car in case they ever need to call on assistance. The third brush could confuse a modern auto electricain, but with the diagram would probably unfathom.
(I know it is dead obvious but some unfamiliar with such diags may not twig that the rotary switch, depicted as linear, is in the side light position)

Bob Culver

Location: Auckland

Having rewired a couple of cars, I find it a good idea (for reliability) to run an earth wire from each component back to a common earthing point on the battery box and thence to the battery. This takes longer and needs to be done carefully so that the many earth wires are protected but I think it is better than relying on an earth return through the body.
I also installed a battery cut-out switch.
Some may say that this is belt and braces but it worked for me.
John

Location: Norfolk, still flat.

Hello JonE. I am the author of the wiring diagram from the Dorset A7 club website. It was an attempt to combine disparate information from several sources, and to draw things in a more understandable "flow" fashion rather than the mechanical "birds eye view" style favoured in the 1930's.

The PLC ignition switch on my car has an internal link between the A terminal and an unmarked one which is one of the inner pair for the ignition switch part. This gives you two places to attach a wire to, which is easier than stuffing two wires into just one terminal. Other examples of this switch may differ of course.

Current flows from the battery via the ammeter and the white/purple wire into the unmarked terminal, through the ignition switch and out again via the IG terminal to the ignition. It also flows via the internal link to the lighting switch part (shown in the SIDE position), and to the cutout via the A terminal and another white/purple wire. Current flow direction depends on whether the battery is charging or discharging of course.

For the starter wiring, I recommend the earth return wire is taken direct from a lug under any of the starter securing bolts straight back to the battery. You also need a lighter gauge earth return link back from the body for the lights etc. This can either be direct to the battery or via the engine block and starter return as the diagram shows. If you don't have this body link then current may flow instead via the choke cable outer, the oil pressure gauge pipe or some other less than satisfactory path.

There is no harm in adding supplementary earth links, but remember that these cars did all work when they left the factory. Assuming no fibreglass bits, I wouldn't bother unless you are getting a significant resistance that you cannot resolve in some other way, such as cleaning under the heads of the bolts that attach the wings.

Location: New Forest

John.. And others.. Thanks.
John.. I tried to email you unsucessfully as I've linked to that diagram on my blog (it was recommended to me by Ruaridh and i too found it very useful.) hope ok to use.. Ive added the Dorset website onto the image.

Interesting the other point about keeping a wiring diagam in the car. I always though one of the 'spaghetti' diagrams would make a good T shirt... But sadly i dont think the images are out of copyright. Perhaps the earliest are...?

Current email is as per my post above, feel free to PM me. The one on the diagram is now out of date as it was from my place of work and I retired 6 months ago when I got to 60 !

Location: New Forest

I notice in John's excellent diagram that the headlamps are shown as 24 watt cf the 18 watt of the handbooks. A point perhaps to watch for those attempting to match dyanamo output to load.

Any introductory guide for new owners should include the Cornwall Club "Charging Refresher" article (with correction!), John's diagram, and a table of original lamp sizes in watts (And original plug gaps, all three ignition timing settings with distributor id, and much more...)

Bob Culver

Location: Auckland