Are these two electrical issues unrelated?

[VicVan]

Yesterday, I adjusted the valves ('90 Auto 2WD Westy).
Today, I took the van to work. On the way to work, everything worked fine.

On the way back, low power, I feel like I'm running on 3 cylinders. I make it home (15 minute ride total), and smell smoke. I open the lid and I see that the smoke is actually the taillight wire heating up and making smoke (right taillight wiring, coming from the left side and crossing behind the licence plate):

(Photos taken a couple hours later, after everything had cooled down).

I then looked into the ignition issue, and found that the distributor cap connector for plug 3 (upper left) makes a spark and is grounding somewhere:

Small hole visible here, at the base of the orange connector:

I'll replace cap and rotor tomorrow. (Last ignition tune up, distrib cap, rotor, wires and plugs was 3 years and 18 000 km ago).

What to do about the taillight harness issue? Cut it open in all areas that I sensed heat in, to check how the wires are doing?
All bulbs work fine, I removed and inspected right taillight; it looked good.

Are the two problems related? Seems unlikely, but the coincidence is troubling.

All bulbs work fine, I removed and inspected right taillight; it looked good.
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[Abscate]

Unrelated.track down the short in the wire by following it across its whole length and look for bare metal
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.ssS!

[MarkWard]

Arm chair stretch diagnosis. The cylinder that was not firing was pushing raw fuel into the exhaust. This could have caused excessive exhaust heat and it was the heat that started to melt the harness. An elec short should have popped a fuse. Have a good weekend.
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☮️

[JudoJeff]

My guess: voltage too high, showing you weak spots in wiring harness. Check alternator voltage regulator.
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1989 Vanagon GL Westfalia Camper, Burned up on 7/31/16.
1987 Vanagon GL Westfalia Camper, Bostig & Rebuilt, sold
1986 Vanagon GL Westfalia Camper, Bostig Sold May 10, 2021
1999 Ford GTRV Westfalia camper (30% bigger Westy layout)

[DanHoug]

that right tail light harness burning is typical of a short in the power steering pressure switch, located on the pump itself. pull the connector off the pump immediately and you may have to strip the harness back and repair wires.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[VicVan]

Thanks for your suggestions.
I'll check for all of these and come back here with some news!
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'90 Little Blue Truck, 2WD auto, FAS GenV 2.0 NA (AVH)

[dgbeatty]

Has anyone ever tapped into the harness for trailer lights?
Do a search for instructions as to installing an extra fuse into the power steering circuit which is unfused from the factory.
Remove the tail light harness and remove the plastic sheathing. Replace any damaged wires.
Check that the fuses are the proper rating.
The failed distributor cap is a separate issue. I suspect the connector on the spark plug end is the root cause. Measure it with an ohmmeter. It should be a aproximately 1k ohm. Not open circuit in any case.

[VicVan]

New distributor cap and rotor is in place. Engine runs fine.
I've started the van and let it idle for 10 minutes, monitoring the harness, nothing happened, no heat, all lights work fine. Went for a 10 minute drive, still nothing.

[DanHoug]

the PS switch is part of the idle control circuit, who's control unit is located behind the right tail light. it is supplied with unfused power from the fuel injection circuit tap in the black junction box on the left side of the forward bulkhead.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[dgbeatty]

It is not the "wire" that could be the problem it is the spark plug connector. The value is usually stamped on the metal shell. It will be good or clearly open, there is no in between. It is a very commonly overlooked failure because few shops use an oscilloscope these days. Older mechanics tend to know how to use them as current engines monitor them and produce a fault code, no skill required other than knowing how to rear.