Reversing Light and Offside Indicators

96 Defender 300tdi original CSW

When I select reverse the reversing light comes on, but suddenly so do the offside indicators and the indicator light on the dash. When this happens, the offside 3 indicator bulbs are on continuously, suggesting that they aren't getting power through the flasher unit. When reverse is not selected the indicators flash normally using the stalk although when I indicate right the trailer light on the dash stays on instead of just flashing once when nothing is connected to the trailer socket. Hazard lights operate normally. This happened without warning - fine on the way to work, but problem on the way home last Friday (not one of the recent very rainy days down south).
I have checked the obvious - reverse light unit fine and it's earth is good. No wet or loose connections in the connectors behind the offside light cluster - behind the triangular metal panel inside the tub. No frayed or loose connections under the rear or obvious damage sections on the section of loom that runs down offside chases leg. Amazingly, the trailer socket is dry inside with no loose connections or shorts.
Disconnecting the reverse light wires from its bulb holder makes no difference - selecting reverse gear still makes offside indicators burn steadily. If I disconnect the reverse light plug above the transfer box the problem goes away, but obviously only because I have no reverse light!
If this was a frayed cable leading to a cross-connection I would have expected an intermittent fault rather than an instant problem.
I have stared at the wiring diagrams and under the vehicle without any new ideas. Anyone with a better brain able to help? Many thanks in advance.

Sounds like an earthing issue to me.

Have you looked behind the panel in the tub on the drivers side as the wiring comes along the chassis up into drivers side of tub then offside wiring and trailer wiring comes out and across .
cheers Ian

Ian Maycock said:

Have you looked behind the panel in the tub on the drivers side as the wiring comes along the chassis up into drivers side of tub then offside wiring and trailer wiring comes out and across .
cheers Ian

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Good call. I'll look there next. From memory, that's where the plugs that connect the rear loom sections sit. It's possible that I have disturbed something during a recent transfer box oil change.

The reverse feed is certainly finding the indicators an easier exit than the intended earth route, so either the earth is more rubbish than it looks, or there is a much 'better' short circuit into the indicators.... Good luck, my 'favourite' problem for investigations....not...... A

Have you found around your ground yet??
It's raining here

I had a similar issue to this, and yes it was an earthing issue, ensure all contacts are free from oxidisation as you'll be surprised how much of a ball ache it can cause especially if it the last thing you check after hours spent looking at less likely culprits.

I've been a bit busy with other stuff for the last couple of days. Tomorrow looks mainly dry, so I plan to follow up on the various helpful suggestions.
It is another classic Sherlock Holmes problem. I can't remember the exact quote, but it's something like: when you have eliminated all other possibilities, the impossible is the answer! In modern parlance that is muliti-metre, multi-metre, multi-metre. I'd rather be doing something fun like changing suspension bushes.

As daft as it sounds as it sounds, have you checked bulb condition?

Gloskris said:

As daft as it sounds as it sounds, have you checked bulb condition?

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All 6 indicator units and bulbs plus the reversing light unit and bulb are less than a year old. I've checked each bulb and the earths to each holder. I'm convinced that somewhere the power to the reversing light is flowing through, or back through, the offside indicators. The fact that the indicators glow steadily suggest that they are getting supplied 'backwards, and not through the flasher unit. In short, all the earths are fine, but obviously they aren't. I will suddenly find the fault - I just hope that I know it when I do!

Widgeon3 said:

All 6 indicator units and bulbs plus the reversing light unit and bulb are less than a year old. I've checked each bulb and the earths to each holder. I'm convinced that somewhere the power to the reversing light is flowing through, or back through, the offside indicators. The fact that the indicators glow steadily suggest that they are getting supplied 'backwards, and not through the flasher unit. In short, all the earths are fine, but obviously they aren't. I will suddenly find the fault - I just hope that I know it when I do!

Click to expand...

Twin filament bulbs can throw up a particularly odd fault symptom and no amount of checking the earth wiring from the bulbholder unit back to the battery is going to sort it out.
The problem is an earth trouble and usually nothing to do with the wiring but the actual electrical contact inside the bulbholder between the earth connection and the silver case of the bulb.
A small piece of emery cloth and maybe a very small screwdriver to prise out the side contact to make sure that it's clean of corrosion and springy enough to make good contact with the case of the bulb is usually all that's required.

Update - all bulbs removed, cleaned and returned to clean holders after checking individual holder earths yet again. Connections behind both rear quarter panels and in nearside gearbox tunnel checked together with connectors to reversing light switch in transfer box. Fault remains! Wild card check of wiring at rear of in cab fuse box - one of very few places were indicator wiring gets anywhere near reversing light circuit - yet more clean connections!
Tomorrow's step is to bypass reversing light supply all the way from the switch in the transfer box to the light holder. Once that is proved I can steadily shorten that bypass cable along its proper path until the problem reappears. Local betting is on a short circuit in the offside chassis leg following last year's rear cross member replacement. The step after that is rolling the whole thing off Beach Head!

Thanks for all the advice on this issue. Finally admitted defeat and sought help from local independent who spotted that the rear loom was rubbing on the exhaust while moving. The cable insulation was damaged alllowing cables to short although the loom cover didn't really show the burning. I'm still embarrassed that, having checked 'everything', I missed this. Now need to save up for a new rear loom to permanently replace the temporaririly repaired section.

We have all missed the simple stuff when looking for the reason for something going wrong!