Mechanical brake light switch on S1 car

Alty Ian · Post by **Alty Ian** » Thu Aug 20, 2015 7:13 am

I am going to upgrade the brake switch from the standard one as they are useless.

Can anyone recommend the best switch type and where to obtain it?

A series 3 one?

Gfhug · Post by **Gfhug** » Thu Aug 20, 2015 7:27 am

Ian, is this more appropriate? Putting an extra switch on the brake pedal:
viewtopic.php?t=3134

Geoff

MarekH · Post by **MarekH** » Thu Aug 20, 2015 8:51 am

Just use one from a Land Rover. It is the same part as on on the s3 etype.

kind regards
Marek

Post by **Heuer** » Thu Aug 20, 2015 11:10 am

I used the 'Intermotor' BMW OEM switch #51690 (fits 3, 5, 7 series circa 1978-93) available on eBay or motor factors. This thread may also be of interest: viewtopic.php?t=6376

Alty Ian · Post by **Alty Ian** » Thu Aug 20, 2015 7:05 pm

Thanks for that guys, I dont particularly like the plastic after market ones that are supplied on the S3 and so have got one of each of the above ones.

The original one and a brand new hydraulic switch I got do not work

But will keep it in circuit for originality and as I dont want to blank off or butcher the wiring there either.

Post by **Heuer** » Thu Aug 20, 2015 9:26 pm

You can use a VW Beetle hydraulic switch which may be more reliable but the mechanical switch is the way to go.

Alty Ian · Post by **Alty Ian** » Thu Aug 20, 2015 9:39 pm

Does that have the same thread Dave?

Post by **Heuer** » Fri Aug 21, 2015 10:17 am

Not quite, but it seems to screw in OK and is leak proof - Lucas used a taper thread, VW use a parallel thread. Being a VW part you are never likely to have to replace it anyway but it screws out without problem and you can screw in an original again if you so wish. Happened to me in Germany and a local mechanic proudly pulled out a boxed VW (1950 - 1966) switch and fitted it. As soon as I got home I foolishly took it out and tossed it, replacing it with the 'correct' repro one which promptly failed

As did its replacement

Hence I went down the mechanical switch route leaving the failed switch in place and still connected. I don't think original VW switches are available anymore so you are lumbered with the repro units which seem to be just as unreliable as the E-Type ones.

Here is a dismantled switch and you can see how the diaphragm operates a pin which presses on a metal 'biscuit' which in turn is held away from the contacts by a spring.

Applying the brake causes fluid to move the diaphragm, pin and biscuit to make a circuit. Unfortunately the contacts arc with the 3 amp load as you can see from the two examples below. The arcing causes a build up of carbon and the switch quickly fails:

From what I can gather the original Lucas and VW switches had heavier gold or silver plated contacts which prevented the arcing but for cost reasons they now use non precious metal. Keeping your foot on the brake when stopped in traffic makes things worse - a practice that was not common back in the day. If you are wedded to the idea of retaining the original hydraulic switch you need to install a simple relay to remove the load:

This is a safety related issue so I strongly suggest you consider one of these modifications if you have not done so. Being rear ended will probably mean the end of your E-Type driving days!

Alty Ian · Post by **Alty Ian** » Fri Aug 21, 2015 12:15 pm

Superbly informative as ever Dave, thanks.

I always planned fitting a mechanical switch anyway, I just expected that a new hydraulic one would get me going, how wrong I was

Post by **Heuer** » Fri Aug 21, 2015 1:02 pm

The installation is so simple using the bracket design Angus posted and the BMW switch. Once you have made the bracket (~ 1/2 hr) installing it and connecting up takes about 20 minutes - probably quicker than trying to get the hydraulic switch out! No one would guess it is there, if that concerns you, and you can leave the original switch and wiring in place as a backup. I think Angus is offering a kit or at least he had the brackets made for his own use.

Alty Ian · Post by **Alty Ian** » Fri Aug 21, 2015 1:11 pm

Yes I saw that and I doubt it will take me that long as my dash is open top and bottom while I finalise the wiring/testing etc.

Its such a simple and effective solution, all e types should have this upgrade 8)

Alty Ian · Post by **Alty Ian** » Thu Sep 03, 2015 6:44 pm

So I bought one of each, went on holiday and then,...

The intermotor one was out of stock after they accepted the order, but the Bearmach BR1448 land rover one came, fitted it tonight and guess what, its the wrong one as its normally open and the switch must be normally closed as the intermotor one is. Brake lights on until depressed when they go off !

So, dont buy the Land rover one above (pity as its really well made).

So re-ordered the intermotor one that Dave has used.

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Mechanical brake light switch on S1 car

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