Need some guidance here. 88 xjsc V12
I was bleeding my cooling system and had the car idling high at about 1000 RPM, heater on full.
After 20 min or so started smelling smoke, and it was getting worse fast. Shut the car down.
The smoke was coming from the quarter area I. The right rear below the speaker.
I tore out all of the storage area and trim and found a burned section of the main harness where it passes above the wheel well, and back to the ECU.
Pics below. My question is, how the heck do I derive the root cause???
i can repair/replace the harness, but I’m worried I won’t know why it happened.
Many suggestions??
Thanks in advance.

Chris

 

It looks like the wires that got the hottest were both smaller gauge, and light brown with cream colored stripe. They both go into the relay nearest the front of the car, just above the battery.
They melted through, or nearly so, in two other locations in the harness, although not nearly to the degree the area in the pics did.
Appreciate any advice!

Thanks
Chris

 

Normally I look for any sharp metal edges or similar that would've chaffed the wires...causing a direct short-to-ground. At a glance I don't see anything like that in your pics.

Perhaps a fault in one of the relays? Any sign of melting/charring there?

Cheers
DD

 

Doug
thanks for the response. No sharp edges that I can see. The relay itself, actually both of them above the battery, were hot as I shut the car down. So perhaps an issue there.

Is is it worth trying to track down where those particular wires go and what they do to look for more if a clue, or is it basically a matter of replacing the harness, relays, and anything obviously impacted and hoping for the best?
Thanks again. Chris

 

This is really a blessing. This could have resulted in your car on fire in another, almost any other scenario

 

I repair the damaged wires, check or replace the associated relays, and see what happens. But, yes, find out what the wires do for more clues, absolutely. Do you have an S57 wiring diagram? If not, I can send one



Cheers
DD

 

Damn.

The relays in the boot are:

RED socket = Main Relay, and it powers up the ECU and the fuel pump relay.

BLACK socket = Fuel pump relay.

I agree with all, something has "overloaded" those wires seriously.

Not to make light of your situation, you might need some of this, cheerful bunch we are.

 

Thanks all...

Grant,
Im pretty sure I’ll need at least two jars of smoke....

Doug,
would appreciate the wiring diagram if you could send.

Does anyone one know if I can buy a new replacement harness anywhere rather than one by one repairs?

thanks!!

 

Chris, they are NLA. The repair should be pretty simple, just unwrap the loom outer and ensure you get all the scorched wires cut out. I use these things, heat shrunk over the wire which are pre-twisted together:

Greg

 

Good suggestion, Greg. Thanks.

 

So, here’s an update.

I started unravelling the harness ness as it moved forward into the front of the car.
The two suspect wires would be ok for a distance, and then have more burned insulation, etc.
so now, the carpet, seats, and console are out.
There is a section of the harness where the two brown/cream wires had burned through their insulation, and the tape was opened. Much of the tape around the wire bundle was like that, as if someone had cut it open previously.
I found one section adjacent to the passenger seat that had wire fully exposed, and a lot of old corrosion surrounding it. Pics below.
There was ample rodent evidence under the sound deadened pads, and around the harness. The padding was all water damaged and still somewhat damp.
Mim assuming it likely at this point that there was a combination of rodent damage, exposed wire, and wet carpet padding that caused the problem.
I’m replacing all of the damaged wire, associated relays, padding and carpet at this point.
All of the roof and door seals are new by the PO, but there may still be leaks I’ll have to watch for.

 

So, here’s an update.

I started unravelling the harness ness as it moved forward into the front of the car.
The two suspect wires would be ok for a distance, and then have more burned insulation, etc.
so now, the carpet, seats, and console are out.
There is a section of the harness where the two brown/cream wires had burned through their insulation, and the tape was opened. Much of the tape around the wire bundle was like that, as if someone had cut it open previously.
I found one section adjacent to the passenger seat that had wire fully exposed, and a lot of old corrosion surrounding it. Pics below.
There was ample rodent evidence under the sound deadened pads, and around the harness. The padding was all water damaged and still somewhat damp.
Im assuming it likely there was a combination of rodent damage, exposed wire, and wet carpet padding that caused the problem.
I’m replacing all of the damaged wire, associated relays, padding and carpet at this point.
All of the roof and door seals are new by the PO, but there may still be leaks I’ll have to watch for.

 

DAMN.

Good find on your part, well done.

I would check the A/C drain hoses, well known to clog and wet the carpets etc.

At least you will have peace of mind now.

 

Grant,
Thanks for heads up on the A/C drains. I got under there this morning to check. The driver's side appeared fine. The passenger side (wet side) had a ball of tar literally wedged into the end of the tube. it was completely blocked. Coincidentally, I got the A/C fixed 3 weeks ago, and have using it daily since.....

Smoking gun found.

THANKS!

 

Guys,
Here's where I am in this repair;
1. Replaced all damaged wires and taped up the harness.
2. When I reconnected everything to start the car, it has battery power (12+ volts) but the starter does not turn.
3. if I leave the ignition on, I can feel the harness starting to get warm. Cools as I shut it off.

So there's clearly a root cause problem yet unresolved. The suspect wires both went to the same pin (87) in the relay inserted into the black socket above the battery. They are both light brown with a cream stripe.
With my limited understanding, I plan to replace that relay, and the starter relay. Possibly the ignition switch????

I'm not clear on exactly what those wires go to, other than I can see them in the engine compartment in the harness that goes to the "inhibit" relay.

 

Possible issue...
i read in another thread that the “fuse able link” was sensitive, and could prevent the starter from cranking. I don’t understand what it does, but mine does not look. Like the one in that thread. It looks like exactly half of it, with a piece and two wires missing:


Can anyone help me understand this?

thx!!!!

 

The '88 diagrams don't show a fusible link. I think those are just unused B+ wires.

Cheers
DD

 

Thanks Doug.
Mess hoping it might have had something to do with my new no start issue.
Car was literally running, and I **** it down when the harness started smoking.
Now, with the harness repaired, the starter doesn’t turn, and I can feel the harness heating up.
Root cause somewhere.....

 

Aren't those are the wires to the fuel pump and something else, (I forget)?

 

They are the Battery HOT wires to the relays in the boot, as in MAIN (Red Socket), and FUEL PUMP (Black Socket).

What you have snapped is NORMAL, and JUST FINE.

My wiring schematics are in the shed, and its midnight here, and COLD, So I will look tomorrow and come back with findings.

Those 87 wires from the Black socket do different things based on different markets, so I will find the USA diagram, as ours will be no use.