Hi all,
Been rewiring my 1983 SIII 109 diesel, using Autosparks looms and the Haynes Book of Lies

Everything is working except for the brake warning light, which I have not been able to get to work properly. It's the self-testing type, with a square "BRAKE" warning lamp which should illuminate when the key is turned to test the bulb, rather than the type with a manual button. It is operated by the shuttle valve on the brake lines under the driver's footwell, and doesn't have any sort of vacuum or servo connection. I'm using the LR340 loom if that's any help, and am running a Lucas 6RA relay in the aux panel on the dashboard.

When I had it plugged in, it came on with the oil and charge lights with the key turned, but went out with the glow plugs and starter. It came back on once the engine was running and wouldn't go out. Tried the red/white wire on different pins behind the ignition switch and this made the relay click whenever the battery was connected/disconnected and the light didn't come on. Also stopped my wipers and indicators working luckily they came back with the brake warning loom's white wire disconnected from the fusebox.

Here's the relay and bulb holder:

And here is the light on the aux panel [above rear guard light]:

This is what I think I have done, but it may not be correct as the diagrams I have got don't show any sort of brake warning circuit. Hopefully this diagram is helpful to someone, assuming it is correct that is! Couldn't find one so had to draw my own, but this is only based on what I've wired up and isn't necessarily right.

Any help would be greatly appreciated, as I have an otherwise fully functional electrical system [not something I'm used to] and would like to get this working properly.
Cheers

Calling @mystery ,
I have one on mine too but can’t recall whether it just lights up if shuttle valve moves in a fault condition not seen it on for years

steve2286w said:

Calling @mystery ,
I have one on mine too but can’t recall whether it just lights up if shuttle valve moves in a fault condition not seen it on for years

Click to expand...

funny I was thinking the same thing with the one in mine. never seen it lit, certainly doesn't test light with ignition and no idea if it comes on with brake failure.

try attached

mystery said:

try attached

Click to expand...

Cheers, my relay only has c1, c2 and W1, so do I just earth to c1?
This is the wiring that was on the relay before I took it out.

Light comes on with ignition, goes out when running. Lights when a pipe leaks.

W2 coil must be earthed through metal body but check should hear it activate when 12 volts applied to W1

mystery said:

W2 coil must be earthed through metal body but check should hear it activate when 12 volts applied to W1

Click to expand...

My relay doesn't have a w2 spade connector, only W1, C1 and C2. I can hear it click when 12 volts is put through W1 but the bulb doesn't light up. The bulb comes on if I put the other end of the W1 red and white wire on the stage 2 live from the ignition barrel.

as attached

Sorted!

mystery said:

as attached

Click to expand...

I couldn't work out that W2 was the relay body and not a spade connector
All working now, thanks everyone for advice and especially @mystery for diagrams!