Series 3 Brake fail harness

As part of my S3 rebuild, I got a 'set' of new wiring harnesses from Autosparks, including LR340, brake fail harness.

Does anyone happen to have a wiring diagram for this, or be able to advise quite how it should be connected?

I thought it was pretty obvious, and I've got it hooked up to the shuttle valve, servo switch and indicator light in the centre dash panel. But I've got a black/white cable with a spade connector that I'm not quite sure where it's supposed to go.

Is that for an ignition switched supply?

Thanks,
Adam

I don't have a diagram but I do have the following, it's not my work but was passed to me by someone on LRUK when I made a similar request to yours, it was sufficient for my needs as I couldn't find a diagram either:

Brake failure warning circuit.

The wires from the brake sensors (servo and Shuttle valve) are black with white trace.

These go one to the bulb.......and one to C1 on the relay.......The white wire on the bulb will be a fused live from the fuse box.

The sensors work by making the black/white wire in to earth when they activate.

The relay has a switched live from stage 3 (starter) on the ignition switch, I think white and red. (W on the relay)

The C2 on the relay needs to go to earth........

So when you click the ignition and activate the starter the relay creates a contact between C1 and C2, linking earth to the black/white wire and thereby illuminating the bulb so you know it works. When you release the ignition back to stage 2 the relay circuit is broken and the light goes out, only coming on if the sensors indicate a fault......

Fantastic. Thanks, @Extreedoc. That's really useful.

Relay...I didn't expect to need one of those! I may just add a manual momentary toggle switch instead for testing, but it's useful to know that's what the white/red wire is supposed to be used for.

I also need to work out what I actually did with the white wire from the bulb....I *think* I ran it to the fuse box.

I should have asked this before hooking up anything at all!

Cheers,
Adam

TheMegaMan said:

Fantastic. Thanks, @Extreedoc. That's really useful.

Relay...I didn't expect to need one of those! I may just add a manual momentary toggle switch instead for testing, but it's useful to know that's what the white/red wire is supposed to be used for.

I also need to work out what I actually did with the white wire from the bulb....I *think* I ran it to the fuse box.

I should have asked this before hooking up anything at all!

Cheers,
Adam

Click to expand...

The relay is a 6RA if that is any help, and it lives behind the little auxiliary panel in the middle where the 'Brakes' warning light is.
John

Extreedoc said:

The relay is a 6RA if that is any help, and it lives behind the little auxiliary panel in the middle where the 'Brakes' warning light is.
John

Click to expand...

Ah, yes, that makes sense! Thank you so much!

When I wired mine up I used the diagram in the workshop book, that didn't show a relay and just wired into a toggle switch to check the circuit.

Guess you have seen this

No relay.

I can't see why it needs a relay to switch on a lousy 5w bulb but it has one and I can't be bothered to figure it out. I would certainly not bother with the relay if I had it to do over again. All I know is that mine has the relay and the harness to wire it all together.

steve2286w said:

Guess you have seen this

Click to expand...

No, I'd not seen that. I really should have checked the book more carefully! I was expecting to find the details in the wiring diagrams, and as there was nothing there, I assumed it just wasn't covered.

The relay does seem a bit of an overkill, but I did remove a 6RA from the back of the aux panel, but didn't make a good enough note of how it was wired in. The previous owner had fitted a rear fog light and heated rear window, so I guessed it was related to those, and I was going to redo all the wiring for those, so didn't need to understand it all...or so I thought! Now it all makes a lot more sense.

TheMegaMan said:

No, I'd not seen that. I really should have checked the book more carefully!

Click to expand...

I must admit I found it by accident.

The thing that's really thrown me here, is that the end of the loom that I've fed down to the switch on the servo, contains a black/white wire (as expected) but also a white/red wire, with a take-off tab on the spade connector. So I figured both wired connected to the servo switch. But clearly, I should have the black/white wire plus a ground, instead.

Why does the white/red wire on the brake fail loom go into the engine bay?!

I was wondering if I'd fitted the loom the wrong way around, and those wired were supposed to go to the aux control panel, instead...but I've got the end of the loom there that has the lamp, so it must be the right way around.

I think all I really need to do is put the earth on the servo switch, as I should have, then I can run another black/white wire from that to a relay and use the white/red wire to mount a relay close to the servo, and that can be the start-induced lamp test relay. No reason why it has to be up by the lamp, is there?

And I think I did connect the white wire up to the fuse box, so I think that'll all be connected as intended...

Its hard to tell what goes to where but if there's a take off tab on one of the spades is it to run to the next switch in the failure circuit?
Its a very simple circuit with a +ve to one side of a lamp and a -ve taking an earth from the various switches to the other side of the lamp.
I'd forget about putting it into a relay as that's just confusing the issue with unnecessary wiring......
http://www.expeditionlandrover.info/Lucaswirecode.htm
I used this chart as a rough guide to what goes where, I know some bits are missing but its a basically handy thing to print out and keep in the workshop book.

I don't have the Autosparks loom, but I spent some time making the brake warning light work on my 109 military, which has a "press to test" switch.
I think the white/red wire in your loom might go to the starter solenoid, with the extra tab for the wire from the ignition switch. Then the other end goes to the relay in the panel, as per diagram below.
As RodeoJoe says, it's a simple loop, one end of the loop goes to the warning light and then to the PDWA switch, then to the vacuum loss switch on the servo and the other end of the loop goes to the relay (or the press to test switch if you have one).
It does seem complex using a relay to test the warning light each time you start the engine - maybe this was a legal requirement at the time? I know this system was standard on the Stage1 but optional on Series 3.

The piggyback spade connector is on the white/red wire in the engine bay, so not for cascading the brake fail switches. The other end of the wire where it comes out behind the dash, had a regular single spade connector. I replaced it with a piggyback spade so I could attach it to the starter switch. I wonder whether the wire was placed incorrectly into the loom, and the piggyback spade was supposed to be behind the dash on the starter switch (as @ExMil109 suggests), and the other end (standard spade) coming out in the central aux panel, next to the lamp. Seems an unusual error, but it would make more sense than having it coming out by the servo.

The is, of course, a white/red wire in the main loom that goes into the engine bay for the starter solenoid. The wire I'm talking about above is an extra wire as part of the brake failure loom, so shouldn't be needed for regular starting/running.

As I said, given I have a 'start' wire and a 'brake fail' wire in the engine bay, I may as well wire up a relay just there. It should work just as well, even if it's in an unconventional location. Yes, I agree it's an unnecessary complication, but it does have the advantage I don't need to drill a hole for a switch in the dash....