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Defenderlad224

Member Since: 30 Oct 2023
Location: Yorkshire
Posts: 2

Td5 interior light earth - dash warning lights on w/o key

Over the last six months or so I’ve been helping my friend rebuild his td5 defender (2001)

It’s been a nut and bolt job onto a new chassis and bulkhead.

Prior to putting the wings on we throught we ought to make sure it turns over.

As part of the rebuild we cut the unused and unusable immobiliser unit out, this is the black box unit that has a handful of black wires coming from it which appears to be a factory unit though it’s been soldiered into the dash, seemingly utilising 2 earths, a purple constant live and a wire that I think from memory is white with a green trace.

On attaching the battery for the first time with no keys in the dash lights came on (glow plugs, oil, and battery ) and the temperature gauge went to the max position and stopped - no response from putting the key in and turning it.

Reading in panic on the forums and something said about the interior light which at this stage wasn’t attached - attached it and found no change.

Next wired the immobiliser I’d cut out back in by identifying the earths and rejoining them then guessing at the other wires (all the wires being black it was anyones guess ) the immobiliser fuse box never had any fuses in when it was removed and still doesn’t so I can’t see how reconnecting it would make any difference other than to attempt to put it back in a state it was pre rebuild when everything was working.

Anyway playing around I found if I earthed the interior light earth direct to the the bulkhead the temperature gauge went down, and the dash lights are not then on without the key present, and all behaves as it should.

I’m flummoxed as so why this should be I don’t understand the td5 wiring and we only cut the immobiliser because it was out of use and my friend who had rebuilt his 110 had done the same for the same reasons.

I’m feeling responsible me being the one who did the cutting but I can’t understand why earthing the int light earth makes everything OK, I’m trying to get my head round what’s wrong and why the int light has such a bearing on this apparently essential function - when fitting in situ the int light just earths back to the bracket which doesn’t seem to ever have been screwed direct to the roof but just sitting in the roof lining

Totally confused - we can get the engine to turn over (wouldn’t know if it would fire anyway as no fuel in currently) and the dash and keys all function correctly but only if I earth the interior light earth to the chassis - as soon as you take that earth away nothings very happy.

Can anyone help educate me on this section of the loom and why the interior light earth would affect the ignition, and temperature gauge and allow the glow plugs and so on to work without any keys seems very odd!

Looking forward to hearing from you,

James

30th Oct 2023 9:46am

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6484

2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

There’s no factory fitted box with all black wires behind the dash soldered into the loom. This is aftermarket, but undoubtedly the cause of your problems.

What colour wires were the black wires to/from the immobiliser unit connected to?

What you need to do is restore the wiring back to factory standard. With the colour info I’m sure we can help.

1988 90 Td5 NAS soft top

2015 D90 XS SW

30th Oct 2023 10:26am

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6484

What interior light earth, do you mean the instrument illumination or the roof light?

Which wire (colour) are you earthing to make things work?

1988 90 Td5 NAS soft top

2015 D90 XS SW

30th Oct 2023 10:28am

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 796

2002 Defender 110 Td5 DCPU Chawton White

It's not overly complicated and you should be able to trace back all the wires surrounding you ignition switch. Looks like you have an issue on how the power is distributed since things are switching on that should not

30th Oct 2023 10:42am

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6484

The other thing to check is that you have ALL the earth ring terminals correctly fitted - including:

* the one which looks like a white/grey connector but has a ring on it, this goes behind the coolant expansion tank.
* the one in the seat box near the fuse box front bracket

Devices finding a earth path through each other does weird stuff

1988 90 Td5 NAS soft top

2015 D90 XS SW

30th Oct 2023 12:02pm

Defenderlad224

Member Since: 30 Oct 2023
Location: Yorkshire
Posts: 2

Thanks for the help so far, pretty well versed with defenders but my owns a 200tdi so not nearly so much gubbins to go at.

The immobiliser is frustrating but I actually think it’s not the cause of the problems what so ever at this stage, it might well become a problem when it turns over and doesn’t fire - but for now that can be an issue for another day.

I think martins probably on the right track in that we’ve missed some earths. When i write of the interior light earth there appears to be a black wire with a single spade terminal that goes onto a spade on the interior light back plate (as in the light in the headliner)

Forgetting the immobiliser our first thoughts was that the ignition switch was wired wrong - but it seems correct to all photos we have of it prior to disassembly and matches every online image and diagram I can find.

So starting again - what earths should I have, around the bulkhead and dash, I’ll find these and make sure everything’s where it should be for starters.

The ECU is definitely earthed in the bottom of the box, there are two thick black earths that come out the loom separately at the back of the engine that are earthed to the engine, it’s difficult as three of us have been working on and off over a protracted period so the person who refit something wasn’t necessarily the person who removed it - the potential for things to have been missed is fairly huge!

30th Oct 2023 4:18pm

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