Ulster Rep Wiring

[Ned]

Hi all,

I'm working with Erich on putting together the ulster replica, and we're having some confusion with the electrical system that I was hoping to clear up.

It looks like we have a 1929 switch panel, and we're going with a 6v system, and we're trying to determine the current capacity needed for each connection. 

Currently we have headlamp assemblies rigged for 6v, with the main bulbs running 35W and the side bulbs at 5W, and tail with 21W for the brakes and 5W for the taillights.

As for the rest of the components in the system, namely a 6v klaxet horn, distributor, coil, cut out, and dynamo, as well as the battery to the switch panel and starter, we're not sure what current capacity we need.

Also, should we think about grounding the lamps to the battery, or is the chassis fine? Thanks!

[Chris KC]

Hi, there's advice on wiring sizes here: https://www.austin7.org/TechnicalArticle...dThin.html
or on p215 of the A7 Companion. Take care not to confuse metric and imperial wire sizes.

I would advocate using the largest wires you can physically fit in the connectors / grommets, in order to minimise resistance losses;
and wherever possible run an earth wire back to the battery rather than relying on earth through mountings etc. With this approach and a sound dynamo A7 6V electrics are quite adequate for most purposes.

["Slack Alice" Simon]

Good advice.

With only six volts, any loss is a big one.

So use as big a wire as you can, never mind the theoretical specification.

Including, if you can, oversize the starter cables.

Run earth wires for everything, don't rely on chassis or bodywork.

The earth wires will carry the same current as the items they are serving.

I use one common earth point near the battery for the rearmost items, and one near the dashboard for the front end, and run substantial cables back to the battery, to avoid too much clutter at the battery itself.

[John Cornforth]

Hi

Those 35 watt headlamp bulbs are a higher rating than would have been used in 1929. The switch panels have fairly chunky internals, so you should be OK. However, for peace of mind I'd be inclined to use a suitable relay which can be tucked away somewhere out of sight.

The total load can be reduced a little by employing LED tail lights, if strict originality is not important.

Personally, I have never had any voltage drop issues when simply using the chassis and bodywork as an "earth" return, provided any joining bolts are clear of paint. It worked fine when these cars were built. It's easy to use a modern voltmeter to check the volt drop between the return of any bulb and the battery, this should be less than about 0.2 volts with the bulb illuminated.

[stuartu]

I favour separate earth wiring myself in the faint hope that I will avoid turning the whole car into a battery when it gets wet. Most of my Austins have aluminium bodies. 
It makes me feel I’ve tried. Possibly a good thing too if you are using leds.

Regards,

Stuart

[Tony Griffiths]

This might help you to decide what to do with the lights,
Improving the lights: http://www.lathes.co.uk/austin7-2/page18.html