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Bees2699

Member Since: 20 Feb 2024
Location: Exeter
Posts: 3

1989 Defender 110 200 Tdi CSW Coniston Green

Reverse Light Wiring

Hi Guys,

First post on here, I have just got a 1989 LR 110 CSW. Has been converted previously to a 200tdi disco engine. Has a LT77 gearbox.

I noticed the reversing light wasn’t working and assumed it was a lamp or fitting (planning to upgrade to LED fitting in the next few weeks so wasn’t to worried. However I have just installed my reversing camera and cut into the reverse light cabling. The camera is now permanently live.

The reverse switch in the gear box is fine I’ve done a continuity check and it opens and closes as expected. I traced the wiring to engine bay and it seems to be wired with the the reverse switch making and breaking the ground connection. The positive feed runs straight to the reverse light, however there is what appears to be a split in the cable which feeds a relay. Not sure what the relay does but has a conductor fed from a terminal which is floating.

As I have continuity to ground at the light end and the switch is open I’m assuming I have a short to ground on that cable.

If I ground the light properly locally to the chassis can I run the positive through the gearbox reverse switch instead.

The cable run is quite straightforward so will likely just renew the cable when I run in some other new cables for various additions. But wanted to make sure switching the positive was suitable.

As a sparkie we can never switch the neutral but that doesn’t seem to be a rule on cars

The wiring comes from the main loom on purple out to the reverse switch on green and back again on green/brown. This then feeds black out to the light.

The positive comes from the loom on green, down to a split on orange and white. Then a red goes to a relay and the other red is the positive direct to the light.

Hope someone can understand the above.

Will add some photos below.

Thank you

24th Mar 2024 4:16pm

Bees2699

Member Since: 20 Feb 2024
Location: Exeter
Posts: 3

Photos in gallery

24th Mar 2024 4:20pm

custom90

Member Since: 21 Jan 2010
Location: South West, England.
Posts: 20371

Did this happen before the addition of the camera or after?

For the reverse camera how have you got that ran?

On mine the camera is always on with ignition live, but the reverse line signal goes back to the HU so there is auto display on screen, or I can use it manually by the screen settings.

Bizarrely years ago I had a situation where the standard reverse light was intermittently working, but when an LED was fitted it was fine forever and still is.
I can only but imagine there was high ground impedance under load, when tested with DMM it checked out as okay.
Some time after that I had more rear lighting issues, and at was tracked down to the rear light loom ground on the RHS of the transmission.
This was after clutch changes, it was loose.
I am unsure as to if that ground is shared with the reverse light, but it defiantly is the rear loom and indicators.

I didn’t get to the bottom of it, and like you the reverse switch when tested showed as okay.

The reverse feed should be used as a live switching signal (very little current) to the head unit, rather than any form of power supply, though granted a camera uses very little current anyway and load for bath can be under the max for that circuit if the reverse light is swapped to an LED unit.

You may well find if you fit an LED reverse light it’ll sort that out, or it could be that RHS transmission ground point.
It has two shared grounds for the rear look on it, on an Approx m6 or m8 stud, and it can become loose.
This is in addition to the main battery ground.

Possibility there is a loose fuse holder, or connection popped off I the rear of the fuse box also.

It’s quite common to have reverse light problems on Defenders, I’d imagine it’s still likely due to the switch and it’s unreliability, possibly mechanical wear and tear. $W33T $0U7H3RN $UG4R
🇬🇧🏴󠁧󠁢󠁥󠁮󠁧󠁿🏴󠁧󠁢󠁷󠁬󠁳󠁿🏴󠁧󠁢󠁳󠁣󠁴󠁿🇮🇪🇺🇸⛽️🛢️⚙️🧰💪

24th Mar 2024 4:38pm

Bees2699

Member Since: 20 Feb 2024
Location: Exeter
Posts: 3

Reversing light has never worked even though bulb filament is fine. However the fitting is old and broken so the terminals are starting to corrode. Initially I assumed there was no voltage or blown lamp. So was surprised when I fitted the camera that I had permanent 12v supply. The camera is wired with a 12v + and - from the reverse light straight to the camera and then an rca cable under the chassis to the head unit. The cable has a trigger wire coming from it which is connected to the trigger cable for the head unit.

I’m assuming it’s a grounding issue so will check and see if I can see any joins or damage. I would assume that if the ground is being switched it shouldn’t be bolted down anywhere but someone may have cut into else where without realising.

Annoyingly because it’s permanently on the trigger is also permanently on so the head unit is stuck on camera mode. I have removed the 15a fuse to the reversing light to kill the camera so I can use the radio still.

I was thinking ground could be dodgy but the camera picture is fine, it doesn’t seem to cut in or out which I would expect if it was loose.

24th Mar 2024 5:35pm

andy63

Member Since: 30 Jun 2023
Location: north east
Posts: 515

are you sure about the reverse switch on the box been a ground switch...
I don't know anything about older models and perhaps someone else can say for sure , but id be surprised.. all the wiring dig ive seen for the later defenders have the light fittings earthed and its a switched posotive supply from the gearbox switch which operates the light ...

24th Mar 2024 7:27pm

Martin
Site Admin

Member Since: 02 Apr 2007
Location: Hook Norton
Posts: 6605

2015 Defender 90 Puma 2.2 XS CSW Montalcino Red

All 90/110/Defender reverse lamps should be switched on the positive side, so for it to now be earth side switched means someone's fiddled with it. Possibly as part of the engine conversion, but wouldn't be necessary for that.

1988 90 Td5 NAS soft top

2015 D90 XS SW

24th Mar 2024 8:43pm

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