Classic LIGHT SWITCH ISSUES 1982 3.5 V8 RANGIE

Here we go again !

So, after replacing the old alternator (55amp) with a new factory spec unit (65amp) as well as the voltage stabilizer on the instrument cluster i went for a drive. It was the evening so i switched the headlights on.

After about 5 minutes, smoke started coming out from under the dash. Stopped and dealt with it. Found what wire melted and its the red wire from the headlight switch. Its got the good ol red, brown, blue combo.

I know that these are prone to corrosion and then a sudden short circuit scenario which is what i believe happened here but i would like some more feedback.

The red wire which is the sidelights one burned from its starting point at the switch all the way back to the rear LH (as viewed from the rear) taillight. So the part that goes inside the car under the headliner and ends up at the taillight. The front sidelights are all fine with no melted red wires.

Now could that be the rear taillight itself that is creating the issue ? The grounds on all of them were clean and sound. Or is the switch the most probable cause ?
The harness has indeed been modified by the Fire Department the Rangie was assigned to and the red wire has one of these dreaded blue plastic clip on connectors out of which another wire goes to what i believe must have been a siren combo unit.

I am going to replace the main harness anyway along with the intermediate one and possibly the engine one too as these were part of my plan but in the future. Just wanted to know what you guys think about the possible sources of my issues. It can't be the new alternator i think. It would have had the bulbs go boom first and its own wires hot, right ?

Let me know. Any feedback is more than welcome.

PS

A lights fuse mod will definitely be something of interest on the new harness.

Unlikely to be the switch, a short to chassis is needed to melt a wire. As the wire is melted all the way to the rear, I suspect that is where the short is.

Datatek said:

Unlikely to be the switch, a short to chassis is needed to melt a wire. As the wire is melted all the way to the rear, I suspect that is where the short is.

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Hello hello

Thanks very much ! Gonna check it out and report back.

Cheers !

Datatek said:

Unlikely to be the switch, a short to chassis is needed to melt a wire. As the wire is melted all the way to the rear, I suspect that is where the short is.

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Bearing in mind that there is no fuse / relay on the headlight switch, where would a ''switch short circuit'' be found if indeed the switch short circuited ?

Could it be in any way related to the new alternator ? The voltage meter was in the normal range all the time and the multimeter measurements were fine.

The voltage only dropped when the incident took place which means a short circuit took place. Where though is the issue hehe. Gonna check the rear taillight and back but the taillights ground is fine i believe.

Datatek said:

Unlikely to be the switch, a short to chassis is needed to melt a wire. As the wire is melted all the way to the rear, I suspect that is where the short is.

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Also the rear fog light switch had the Red / Yellow wire break off of it. I don't think that's related though.

Jim_P said:

Bearing in mind that there is no fuse / relay on the headlight switch, where would a ''switch short circuit'' be found if indeed the switch short circuited ?

Could it be in any way related to the new alternator ? The voltage meter was in the normal range all the time and the multimeter measurements were fine.

The voltage only dropped when the incident took place which means a short circuit took place. Where though is the issue hehe. Gonna check the rear taillight and back but the taillights ground is fine i believe.

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As the wire melted along it's length, the short has to be at the opposite end to the supply, therefore the short will be at the rear. If the short was near the switch, then the wire would only be melted to that point. Most switches only have the positive connected so a short within the switch is unlikely unless it has a metal case which is grounded and in that case the wire would not have melted.
It has nothing to do with the alternator.

Datatek said:

As the wire melted along it's length, the short has to be at the opposite end to the supply, therefore the short will be at the rear. If the short was near the switch, then the wire would only be melted to that point. Most switches only have the positive connected so a short within the switch is unlikely unless it has a metal case which is grounded and in that case the wire would not have melted.
It has nothing to do with the alternator.

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Hey there,

Thanks very much for clearing up the alternator topic and the explanation.

That's great advice ! Correct, if its melted along its length then the short must be at the opposite end. Thanks a million !

Would you think a faulty taillight socket could be my issue ? I find it strange though. Gonna test it.

Cheers !

Jim_P said:

Hey there,

Thanks very much for clearing up the alternator topic and the explanation.

That's great advice ! Correct, if its melted along its length then the short must be at the opposite end. Thanks a million !

Would you think a faulty taillight socket could be my issue ? I find it strange though. Gonna test it.

Cheers !

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Certainly bulb holders have been known to fail but I don't know the Classic. Equally, it could be failed insulation where the wire passes through the body to the light assembly.

Datatek said:

Certainly bulb holders have been known to fail but I don't know the Classic. Equally, it could be failed insulation where the wire passes through the body to the light assembly.

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Photo of the bulb holder. The Green / Purple wire has broken off of its base.

Is that under any way a possible cause ? Its also corroded heavily. Rechecked the other side and its fine. Also checked the plate illumination wiring and its also fine.

Removed the intermediate / rear harness and from what i can see the middle section of it is not burned. I will remove the tape to look more carefully but it doesn't look as if the red wire inside has melted.

The parts the of the red wire that melted were on the rear LH taillight and also a length from about halfway up the A Pillar to about the switch.

Strange as i though the whole middle section would have melted too.

Jim_P said:

Removed the intermediate / rear harness and from what i can see the middle section of it is not burned. I will remove the tape to look more carefully but it doesn't look as if the red wire inside has melted.

The parts the of the red wire that melted were on the rear LH taillight and also a length from about halfway up the A Pillar to about the switch.

Strange as i though the whole middle section would have melted too.

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Yes, it's a bit odd that it's not all melted.

Removed the tape and although the Red wire had some heat marks here and there it didn't have and melted parts to be honest.

What in the name is this sort of short circuit ? Could it be a faulty regulator on the new alternator ? Its an NOS unit damn me.

Jim_P said:

Removed the tape and although the Red wire had some heat marks here and there it didn't have and melted parts to be honest.

What in the name is this sort of short circuit ? Could it be a faulty regulator on the new alternator ? Its an NOS unit damn me.

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It cannot be anything to do with the alternator. Check the voltage at the battery with the engine running to set your mind at rest. Duff regulators blow bulbs, they do not melt wires.

Sorted the damn thing !

It was the alternator by the way. Well in general the alternator related wiring and the unit itself. The thin brown wire that gets attached to the spade connector close to the B+ stud is responsible for handling the regulator. So, battery sensed in a way I think.

The Bosch alternator that was on the Rangie when I bought it (this had been installed by the Fire Department when the Range Rover was putting out fires not starting them) did not require this thin Brown wire as it sensed the voltage need / regulation internally. However the NOS Unipart (GXE2887) one is different and required that thin brown wire with the spade terminal to get attached to the male spade terminal near the B+ stud. The NOS unit had no markings on its damn back so I did not put the two together to understand what connections were required.

So it was an overvoltage scenario. Glad its sorted out, after asking around of course and also studying the wiring diagram and the wiring on the car as well as the alternator.

Hope this helps out anyone faced with either a ''how to wire'' dilemma or a similar situation.