Does anybody have any tips on refurbishing the Lucas SM5 switch unit to minimise the voltage drop please?

Many thanks

The only two places there can be any voltage drop is the ammeter and the ignition light, on the assumption all the contacts have been cleaned to give bright metal contact with the wire ends or within the two switches.

I use new screws in the terminals after cleaning with a small wire brush (model makers) and then Brasso or similar, it's out of site so will not be seen for Rally judging! (Patina Points?) The switches are cleaned up with swiss files etc, making sure there are no carbon deposits left, and any over-centre springs are also renewed.

I also solder the wire ends together before connectiing to a terminal on the switch panel, as with all other connections.

Naomi

Good advice from Naomi, but go easy on the filing - fine emery cloth is better. The switchpanel comes apart fairly easily. However, to take account of the higher power headlamp bulbs we use these days, I would advise inserting some relays between the switches and the lights. These can be mounted on a small board and mounted up behind the dashboard. It will take the strain away from 75 year-old electrical contacts and will keep going when the brass bits tarnish again. For more details and other advice, see www.vintageknowledge.co.uk -- click on Hints & Tips, scroll down to Electrical and click on 6 Volt Electrical Systems. Maplins used to (still do?) suitable relays - you need 6V 10A ones.

David

David
There is a very informative article on the restoration of the Lucas SM5 switchboard on the Cornwall Austin Seven Club Website www.austin7.org/ in the Technical section .It's worth a look , MacG

I tried the Maplin 6v relays for Headlamps, but did not have the courage to accept that the 'pins' with a cross sectional area of 0.35mm (I cannot get it to show a small raised 2 after the ..mm) could cope with up to 10 amps, remembering a domestic 240V 5 amp lighting circuit uses wire of 1mm cross sectional area (and 2.5mm for 13 amp).

I went for Stafford Vehicle Components 6v 30amp 'Fused Relay' which have auto spade connectors. I bought mine at last years Bristol Classic show/autojumble at the Bath and Wells showground - next one is this coming weekend. A good show, but little if any specific A7 material, although I did get some very good LB130 headlamps for £50 last year.

Stafford V C can be found at www.s.v.c.co.uk and the 'Fused Relays' are listed under 'Other Products' at £5 + Vat. You will need two of them because these are 'make and break', so you need one for the 'dipped' circuit and one for the 'main' circuit. If you have the confidence to do this then you will not need telling how to arrange the wiring.

What do those Cornish people have that they seem to be refered to so often on this site and in various Newsletters (Essex, Scottish, etc. A7 Clubs), I think they were called 'The New Kids on the Block' recently in one Newsletter, and they seem to make a killing with the prizes at Beaulieu as well. They are nearly all retired now, but then so am I...... Ahhhhhh, that's the secret, young at heart.

Naomi

Thanks everyone. The weakness of these units seems to be electrical continuity on the moving parts. My problem area is between the two switch spindles and brass moving contact 'bridges'. All the brass bits have come up gleaming but the current is not getting there as it should. It looks as if all the moving parts of the switch including the spring are 'live' when the switch is not in the OFF position?

David (which? - could you add your surname please - there are several of us Davids on this forum!) asked:
> It looks as if all the moving parts of the switch including the spring are 'live' when the switch is not in the OFF position?

Yes, I think so (without going out to the garage and pulling one apart to make sure) but is this a problem?

You also say that:
> the current is not getting there as it should

It could be either that the rubbing parts of the brass contacts have worn so much that they no longer make proper contact, or that the springs are weak, or that the moving brass contact part is too tight on the shaft of the rotating switch. Making use of relays helps of course in that only the low relay actuating current has to get through. Other causes could be that one of the brass tracks has fractured (easily mended with brass strip & solder) or that one (or more) of the terminals has come loose from its track. Careful cleaning and soldering will fix that.

Hope this helps!

David