I have a wire left over ;-)

hrgDavid · Dec 1, 2017

Hi,
Please can anyone advise on a earth wire without a home ?

I've redone the wiring in my 200tdi, but I have one reasonably thick brown wire with a red trace that I can't find a home for. It comes out of the main loom just after where the loom exits the bulkhead into the engine bay and splits to go left and right. It's on the driver side, about 4 inches from where the loom splits - and then appears to double back on itself (ending up pointing towards the passenger side - or engine block ?).

I've checked all my old dismantling photos, but cannot see it anywhere (mind, all the wires were coated in waxoyl). I've also looked through various wiring diagrams, but the only brown/red wire I can see is described as "Compression ignition starting aid to switch. Main battery feed to double pole ignition switch". It won't reach either the battery or the ignition switch so I assume it's not that

Does anyone have any idea where it goes ?

Thanks for any help.
David L.

Kwakerman · Dec 1, 2017

On a 300 the brown/white is used for the heated rear window relay, don't know if the 200 is the same.

Disregard, just realise you said brown/red not brown/white

Discokids · Dec 1, 2017

Brown with red is for the glow plugs

Kwakerman · Dec 1, 2017

hrgDavid · Dec 1, 2017

Kwakerman - thanks ! I've just seen that too, but there's no way it will reach the relays (if they're the ones mounted on the bottom of the dash). Judging by it's position, it must go somewhere in the engine bay (I think).

Plus the one thing I forgot to mention earlier is that it has a ring connector on the end of it. I know nothing about electrics - but I assume that's not going to connect to a relay ?

Discokids - thanks ! That seems really likely. Do you know where it bolts to ? As above, it's got a spade connector on it so if I find somewhere on the engine block for it, will that do ?

Thanks both. Really appreciate your help.
David L.

Discokids · Dec 1, 2017

It should go to the glow plug closest to it, then there will be cables from that plug to the next to the next to the next.

Discokids · Dec 1, 2017

Just stick a pic up so we can be sure.

hrgDavid · Dec 1, 2017

Photo attached.

Having checked, I don't think it goes to the glow plugs. They have a yellow wire with a black trace and seem to be all looped correctly - you can just see it in the bottom centre of the photo (plus the engine starts).

Thanks again for any help !
David L

Discokids · Dec 1, 2017

hrgDavid said:
Photo attached.
View attachment 136017

Having checked, I don't think it goes to the glow plugs. They have a yellow wire with a black trace and seem to be all looped correctly - you can just see it in the bottom centre of the photo (plus the engine starts).

Thanks again for any help !
David L

No probs. Where does the wire from the rearmost glow plug go on its way towards the bulkhead?
200tdi doesn't need any preheat to start, unless it's absolutely knackered. Mine fires up instantly even when covered in snow, and the engine is almost completely exposed as there's no wings on the car.

hrgDavid · Dec 1, 2017

It goes into the ignition relay - marked PRC6913....

No wings ? Yours sounds in a similar state to mine ;-)

Brown · Dec 2, 2017

I wouldn't just attach it to the metalwork, as brown wires tend to be some sort of live (like in the wiring in houses). So you could pop something. Can you put a bulb or meter on it and see what makes it live? Eg does it come on with the ignition? Is it permanent live? Does it come on with any of the lights? You might be able to narrow down what it is supposed to do.

jamesmartin · Dec 2, 2017

as above all brown wires are battery live

hrgDavid · Dec 2, 2017

Thanks for your support guys. Sadly my knowledge of electronics is very limited. I thought that because it had a ring connector on the end, it was an earth. Hey ho !

Anyway, I measured the voltage. The battery voltage is 11.9V. (it's slowly being rebuilt and has stood for a couple of years). The brown/red wire is not permanent live - it measures a few millivolts before I put the key in. On the first click, it measures 1.5V and at the second click it measures 3.5V, I can't start the engine as it there's no diesel in it.

Those readings don't change when I put the lights on or the heater (they both work). The windscreen wipers don't work. I need to trace those wires and see what's up - but I don't think this wire is related - it certainly wouldn't reach the wiper motor.

Worst case is I'll put everything back together and see what's missing then. But that dashboard is a PIA to install/remove and I'd rather validate all the wiring before it goes back in again....

Thanks for any clues/pointers !
David L.

tottot · Dec 2, 2017

On my 1990 90 [Was a turbo diesel but been 200tdi for ten years now] that brown red goes to the glow plugs and is operated maualy by holding the key at full movement against the spring. Yours like mine may have been a 19j originaly and when a 200 went in the auto glow relay was also fitted.

Scooby22 · Dec 2, 2017

I have seen two references for this wire, the most plausible one is the glow plug timer and another option for a brown with "orange" stripe (is yours actually brown/red) saying it goes to fuse box to supply other green wire live feeds, which could be wipers.

hrgDavid · Dec 2, 2017

Thank very much guys - I think you're right, Mine is also a 1990 90 and that wire is definitely the right length/position for the glow plugs. But as I said above the glow plugs are looped with a yellow/black wire and work.

I also got the wipers working this afternoon (for a short period before the battery voltage dropped too low) - so, I don't think it's related to the wipers.

I'm going to tape up the red/brown wire and assume that it's excess to requirements.

Thanks again for all your help on this. Really appreciated.
David L.

Gmacz · Dec 2, 2017

It is the glow plug wire worked by the key for about 10 to 20 secs. If you have a wire connected to the circuit then someone has probably put a timer in the circuit and it is now automatic. If it fails, connect the brown wire and use the key to operate them.

Kwakerman · Dec 3, 2017

hrgDavid said:
Thanks for your support guys. Sadly my knowledge of electronics is very limited. I thought that because it had a ring connector on the end, it was an earth. Hey ho !

Anyway, I measured the voltage. The battery voltage is 11.9V. (it's slowly being rebuilt and has stood for a couple of years). The brown/red wire is not permanent live - it measures a few millivolts before I put the key in. On the first click, it measures 1.5V and at the second click it measures 3.5V, I can't start the engine as it there's no diesel in it.

Those readings don't change when I put the lights on or the heater (they both work). The windscreen wipers don't work. I need to trace those wires and see what's up - but I don't think this wire is related - it certainly wouldn't reach the wiper motor.

Worst case is I'll put everything back together and see what's missing then. But that dashboard is a PIA to install/remove and I'd rather validate all the wiring before it goes back in again....

Thanks for any clues/pointers !
David L.

Get your battery on charge, anything less than about 12.7 is considered flat and the battery will degrade quickly if left discharged, if its not being used give it a top up charge every couple of months

I have a wire left over ;-)

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