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Handbrake warning light wiring


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Pic 1 - sub loom joint into main loom. 2x black / white, 1x black to earth.

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Pic 2 - sub loom to switch. 2x black/ white into single terminal, 1x black.

Why do I need  2 black / white wires? I've pulled the plug off the main loom and tested the 2 main loom terminals for continuity, which they don't have so are not connected together. But where do they go? There is only one warning light on my dashboard.

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Thanks Ian. 

It's an awfully long bit of loom to go to the resirvoir cap. 

I've found the wire at the warning light, that's black/white and has continuity to the male black/white at the sub loom plug. I'm still none the wiser where the female black/white goes. 

It's so much trickier to figure these things out when the loom is in the car and not on the bench. 

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 the red park brake warning light with the (!) icon does a few jobs 

1. during pre start it should come on & then go out as a bulb check via the brake check relay in fusebox

2.  if the brake fluid level goes below minimum it should light to tell driver the brake fluid level is low

3.  if the handbrake is connected with the switch, it should light the red light when handbrake is ON.

on my '89 110 I retrofitted the low level float switch cap & joined it in to the existing PDWA wiring which connects at a similar 2 pin connector at rear of the brake pedal housing, I made my own sub loom for the float cap 

 

 

 

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Thanks Ralph. On the old glass fuse loom I took out, I found the wire and traced it back to a relay connector, which would explain the bulb check function. 

I still think that this long sub loom I have should probably go down to the handbrake switch, and I'm missing the bit for the resirvoir cap. 

Ralph, what colour wire do you have going to the handbrake? 

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Handbrake wire is white/yellow trace, IIRC goes from one of the multiplugs by clutch master cylinder down the bulkhead along chassis to handbrake, the other end comes into dash area then to warning light panel connections. 

this is how I fitted my 110 park brake warning light 

 

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  • 2 years later...

Hi folks, 

1994 300Tdi 110 base spec SW

I searched for "handbrake light" posts, and this seemed the closest. I thought it best to add on here, rather than start a new thread on the same issue, but mods please amend if this isn't good practice.

Following my recent questions on my centre diff lock switch I also realised that my handbrake light isn't working. It used to work. It does have a switch, and does have a yellow/white wire to it, and there is a lamp in the dash (though I haven't yet replaced the current LED with the original filament in case it's a polarity question). As in the diff lock thread, it could even be that the flexi printed circuit behind the lights is showing its age. So I'm looking for a bit of help understanding how the circuit works to help with troubleshooting. I tried to find the operation explained in the WSM but couldn't see it.  

Western said above:

"the red park brake warning light with the (!) icon does a few jobs 

1. during pre start it should come on & then go out as a bulb check via the brake check relay in fusebox (currently mine doesn't do this)

2.  if the brake fluid level goes below minimum it should light to tell driver the brake fluid level is low (don't know)

3.  if the handbrake is connected with the switch, it should light the red light when handbrake is ON." (not doing this)

I think there are three possibilities for me

  • LED lamp isn't working/wrong polarity - or the printed circuit board is gone.
  • the yellow/white wire is in poor condition, broken or shorted.
  • that the circuit isn't working because of a bad earth through the handbrake lever?

So, a couple of specific questions after all that. How does this circuit work? There's only the yellow/white wire coming to the lever switch. Does that mean it's a live feed earthed via the lever, or the rest of the handbrake assembly itself? Presume it's only powered when the ignition switch is at position II?

Could I check the low brake fluid warning just by shorting/putting a jumper wire across the wiring at the brake fluid cap? I guess that would help me focus on the lamp itself, rather than the handbrake lever.

As always, any help very gratefully received. 

Thanks 

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300tdi doesn't have a relay for the brake check, as far as I recall. The bulb check for the fluid level is done via a diode to the handbrake switch, so when the handbrake warning lamp is lit, the fluid level warning should also light.

Since you don't have either lamp working, then the handbrake circuit is most likely, but if you just take the cap off the brake fluid reservoir and lift it above the fluid, the fluid level warning lamp should come on. (You can just jumper the wires, but that wouldn't check the fluid switch at the same time)

As you suggested, ground the wire at the handbrake switch, that should put both warning lights on. It's a pretty poor switch design, I'm amazed they work as well as they seem to, I've only once had to replace one.

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Thanks very much. 👍 This will take me a step forward.

  • 300tdi doesn't have a relay for the brake check, as far as I recall. The bulb check for the fluid level is done via a diode to the handbrake switch, so when the handbrake warning lamp is lit, the fluid level warning should also light.

Just to clarify, if the circuits are linked, does this mean that in normal operation, if the handbrake is applied both lights would come on?  Then, if driving along, and only the fluid level light comes on, it's a fluid level issue? 

I've read a lot, and tbh have become confused about what should/should not light. My panel has separate spaces/icons for handbrake, and fluid level, but I'm sure I saw something suggesting that the handbrake light, and the fluid level light were one and the same. Maybe earlier models?

  • Since you don't have either lamp working, then the handbrake circuit is most likely, but if you just take the cap off the brake fluid reservoir and lift it above the fluid, the fluid level warning lamp should come on. (You can just jumper the wires, but that wouldn't check the fluid switch at the same time)

I think I'll do both - jump the wires to check if the lamp or circuit works, and then do it with the switch connected, but out of the reservoir. 

  • As you suggested, ground the wire at the handbrake switch, that should put both warning lights on. It's a pretty poor switch design, I'm amazed they work as well as they seem to, I've only once had to replace one.

In a (probably misguided) effort to separate steel and aluminium I had put a thin PVC gasket in between the lever and the seat box. I'll take that out - but I'd kind of expect that if lever/seatbox contact wasn't available, it would still earth through the bolts and/or the handbrake. 

For context, I did fit a new autosparks loom about 2 years ago, so I can be a little bit confident in that. I didn't replace the flexible circuit then. I think I'll do that now, and probably just go back to the little filament bulbs. This is one place where little LEDs just might not be the answer. 

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46 minutes ago, Northwards said:

Just to clarify, if the circuits are linked, does this mean that in normal operation, if the handbrake is applied both lights would come on?  Then, if driving along, and only the fluid level light comes on, it's a fluid level issue?

That's right. The diode makes a one way path for the ciruit, so the fluid switch only puts on one lamp,but the handbrake switch puts on both.

48 minutes ago, Northwards said:

I think I'll do both - jump the wires to check if the lamp or circuit works, and then do it with the switch connected, but out of the reservoir. 

I'd take the cap out first, if that works, then there's no need to pull the wires off the switch, as it proves everything in one step. Less chance to break something pulling a tight crimp off a tired old switch :rolleyes:

50 minutes ago, Northwards said:

In a (probably misguided) effort to separate steel and aluminium I had put a thin PVC gasket in between the lever and the seat box. I'll take that out - but I'd kind of expect that if lever/seatbox contact wasn't available, it would still earth through the bolts and/or the handbrake. 

I've done the same on my current build. I'd be surprised if it didn't work through the bolts.

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Well, another mix of progress and setbacks/questions. 

I discovered last night that my relatively new Autosparks main loom did not have continuity on the yellow/white wire, between the instrument panel and the multiplug on the bulkhead. Just to be sure that it was supposed to have, I dug out the old loom which I'd kept, and got continuity there. It wasn't just a dodgy pin in the multiplug either as I pushed my tester needle through the cable sleeve just behind the plug.

I did have continuity on the lower wires in the circuit - between the handbrake lever and the other half of the multiplug - on the original 28 y/o loom. 

So, to do this properly I'll need to get a length of yellow/white wire; a connector to fit onto the back of the dash lights; and figure out how to dismantle the multiplug so that I could crimp on a new terminal. I think I'd want to remove my airfilter and air intake pipework for access, so that will need to be a job for a rainy day later in the year. In the meantime I have spliced a length of wire direct from the dash light panel to the handbrake switch, and I have a handbrake light! Yay!

I also checked that the brake fluid light worked, though after all my toing and froing, once I had a working lamp, I forgot to go back and check if the level switch itself was working.

What I don't have is the fluid level bulb lighting up on ignition as a bulb check. Handbrake light doesn't do that either. 

The wiring diagram (97MY) does show that the circuits are connected, and does show a diode, but I can't see it "in real life" in my 94 vehicle. Even with the old loom on the garage floor I'm not seeing anywhere that a diode would live. If there's a connection, I'm sure it's on one of the black/white wires that form part of the fluid level circuit - there are two joined at the fluid switch; and two at the instrument light multiconnector, so I'm assuming it would be with one of them - but where? I could wind off the tape around the old loom, and literally follow the wires, but maybe someone else has been here before? 

End of the day, after starting all this, I have a diff lock light which works, a brake fluid light which (probably) works, a handbrake light, and I noticed that my 'sidelights' lamp was completely missing. So I'm happy I've made enough progress to think about putting it all together - it would just be nice now to see if I could get the 'ignition bulb check' thing to work properly.

But a big thanks for the advice and help getting this far. 

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Posted (edited)
1 hour ago, Northwards said:

What I don't have is the fluid level bulb lighting up on ignition as a bulb check. Handbrake light doesn't do that either. 

The fluid level bulb won't light on ignition only, just when the handbrake is applied (and the ignition is on).

The electrical library says it should be behind the fusebox, and in true high quality LR fashion, it's almost certainly just a diode soldered into the loom and covered in heatshrink rubber tube.

I have a '95 loom in a box in the workshop. I can try to have a look at it this afternoon.

If you have a digital multimeter, it probably has a 'diode check' function (often a special mode of the continuity or resistance test). You should be able to test from the warning light connectors. With the probes connected to the black/white and white/yellow wires, I'd expect a reading of around 0.7V with the probes one way round, and maximum, or no reading, the other way round.

Edited by TSD
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Thanks again,

I've been doing some further forum searching and found information to suggest that while older vehicles did have this function, 300Tdi ones didn't:  "300TDI era trucks do not have a brake light check function.  Earlier trucks did have a check relay.  Both the low level switch and the park brake switch are directly connected to the lights.  The switches switch to ground." (From exMember/Red90)

I'm also going through the 300Tdi wiring diagram with a fine tooth-comb, and I have to say that so far I haven't found any reference to a brake check relay....

If you get the time to check your loom that would be appreciated. I'll certainly be laying my old one flat on the bench when I get home and trying to figure out exactly what happens. But it would be good to know if I'm 'chasing a ghost'!

Even if it is supposed to be there, given that I've completely bypassed the yellow/white wire between the dash and the multiplug, I've possibly removed the link between the two circuits, unless it happens via the flexi circuit board?

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Completely forgot to look at this, two days running :rolleyes:

Anyway, finally remembered to look out the loom. The diode is contained in a small plastic housing, taped into the loom, just below the relay carriers next to the fusebox.

20220709_164840.thumb.jpg.496231c30fbf7d2b186b7b8bae57546d.jpg

Surprisingly well done for Land Rover. In a Discovery 3 they wouldn't even have run to heatshrink tube, just insulting tape!

 

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On 7/9/2022 at 6:49 PM, TSD said:

Completely forgot to look at this, two days running :rolleyes:

Anyway, finally remembered to look out the loom. The diode is contained in a small plastic housing, taped into the loom, just below the relay carriers next to the fusebox.

 

Surprisingly well done for Land Rover. In a Discovery 3 they wouldn't even have run to heatshrink tube, just insulting tape!

 

Hi TSD, 

Thanks for that. I'm slow getting back myself - I was distracted last weekend by changing the front propshaft, diff and halfshafts/CV joints.... as you do! 

Having closely examined the old loom I had, this is the circuit, as far as I can see :

IMG_20220712_110026.thumb.jpg.2da4b13ffaa5b1cb0a2429713ad3d812.jpg

When I was initially focussed on getting the handbrake light to work, once I found that I'd no continuity between nos 3 & 5, I just cut the loom between points numbered 3 and 4 in the dodgy diagram, and ran a wire all the way from #3 to #6 at the lever. I got the handbrake to work OK, but no brake fluid lamp. 

I then checked the old loom more closely and found that this poor looking thing is the connection at number 4. It was just wrapped in a small blue bit of electrical tape. If Autosparks just copied this, it's little wonder it hasn't worked.

IMG_20220710_113838.thumb.jpg.e136175482bc1f233a567116f9006ac3.jpg

One wire goes straight through; one is spliced on. In my "new" loom, I'm pretty sure this connection wasn't properly made in the first place, or has since broken. 

Having understood this connection, it occurred to me that possibly there would still be a good connection between 3, 4 and 7, so I amended my additional handbrake wire to include the yellow/white entering the new loom, and the brake check light worked perfectly. If this hadn't worked I'd have cut the diode out of the old loom and spliced it into a entire new mini-loom for the handbrake/level lamp circuit, but it worked out easier. This leaves me as happy as I can be in the circumstances, but disappointed that I've found one flaw in what was an expensive new loom. I'm not aware of any others, but if I get any other electrical issues, I won't discount the loom itself. 

This is the diode in the original 1994 loom - shrinkwrapped!

IMG_20220710_113750.thumb.jpg.b3fcf980f3289026a440f65a5ae6a19f.jpg

Thanks very much for your help along the way.

 

(PS - I think this is my first time posting pics on this forum, so if they're huge, or wrong someone, happy to try and fix that).

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7 hours ago, Northwards said:

This leaves me as happy as I can be in the circumstances, but disappointed that I've found one flaw in what was an expensive new loom.

What @FridgeFreezer was chuckling about above, was that there's a very similar joint in the factory wiring loom of a Discovery 3, in the cable tray along the door sill. Combined with a water leak caused by poor plastics, it killed the central locking and left my D3 immobilised in a multistorey car park, because the only mechanical door lock is in the passenger door, which was 2" from a concrete pillar. I might still hold a small grudge about that one :lol:

  • Haha 1
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