Harness caught fire

[camron]

A couple days ago my wire harness caught on fire but it only burnt the wires going to the two big plugs on the driver side of the motor. I butt spliced them all together just to get home. Now my speedometer, oil pressure and overdrive don’t work(overdrive I know it’s too working because the speedometer isn’t), and I don’t think my glow plugs are working because the “wait to start” light doesn’t come on when I turn the key. What sensors could it have burnt up and where are they located, or any other ideas on how to fix my problem? Truck will still drive fine but none of those things work.

 

[AnonEd]

I'm not home (where truck and FSM are) and don't have an auto, so maybe no help. Wiring to driver's side probably includes coolant temp sender, fuel heater, WIF sensor, oil press sender, injection pump, crank position, IAT sender, probably more, plus whatever's on the transmission (temp, back-up lights, speed/distance sensor, park/neutral? OD? 4WD indicator?). Memory says the alternator and AC are on the pax side of my truck. Any idea what caused the burn in the first place?

 

[bcbender]

camron, post your truck's details (MY/model/mods) so that those who have a 1st gen can better answer or share the appropriate schematics

 

[Tuesdak]

Disconnect the batteries ASAP! Leave them disconnected until the repairs are done. Just saying you don't want the problem to catch fire again and finish turning your vehicle into say a Real Chevy Blazer.

Are you somewhat good with wiring? If not the frustration and further damage potential is high. Thus you should have an automotive electrical shop put a new or used harness on it or rebuild yours. I would replace every single fuse regardless of condition in case you got some defective knock-off ones that don't blow. Finding the cause will be the tricky part if a sensor, gauge, AC clutch, alternator, etc. shorted and caused the problem. It's possible fusible links were removed (cut out) in the past due to age failure and not replaced.

I would pay close attention to the high current wires: starter, alternator charge wire, battery cables. I have had these flake insulation off from age, rub through on battery trays, sharp edges, and get interesting...

 

[camron]

I have a 1991 LE trim, pretty much stock except for injectors and upgraded internal for injection pump. I have no idea how it started I was just driving down the road and I started smelling smoke. I’m an electrician so I have a decent knowledge but vehicle electric always worries me. My AC has never worked so I don’t think it started there, I checked the fusible link for the speedometer and made it an inline fuse but didn’t help my problem, all my gauges work except for my oil pressure and my speedometer. When I get home I can upload some pictures.

 

[camron]

Most of the ones that burnt up bad went to the black plug

 

[AnonEd]

The distance sensor that drives the speedo and the OP sender signal are very likely in that jumble. I am curious about the "fusible link for the speedometer." AFAI can tell, fusible links feed the manifold heaters, fuses (4,5,6,10, 15), AC and ASD relays, ignition switch and headlight switch...and there is one from the alternator supply.
The OP sender runs 20GY/YL and 20GY wires through 10-pin black plug LR of engine, with 20GY/YL going to pin D and 20GY to pin H on the round right side printed circuit board connector.
The speed sensor appears to run 20BK/LB to a multi-sensor-return splice to pin 4 "sensor return" on the SBEC, and 20WT/OR through a 10-pin connector (color not shown) to a splice with a 20WT/OR to pin 6 of the flat left printed board connector and 20WT/OR to pin 47 "speed sensor pickup" on the SBEC.

 

[camron]

The distance sensor that drives the speedo and the OP sender signal are very likely in that jumble. I am curious about the "fusible link for the speedometer." AFAI can tell, fusible links feed the manifold heaters, fuses (4,5,6,10, 15), AC and ASD relays, ignition switch and headlight switch...and there is one from the alternator supply.
The OP sender runs 20GY/YL and 20GY wires through 10-pin black plug LR of engine, with 20GY/YL going to pin D and 20GY to pin H on the round right side printed circuit board connector.
The speed sensor appears to run 20BK/LB to a multi-sensor-return splice to pin 4 "sensor return" on the SBEC, and 20WT/OR through a 10-pin connector (color not shown) to a splice with a 20WT/OR to pin 6 of the flat left printed board connector and 20WT/OR to pin 47 "speed sensor pickup" on the SBEC.

Where is the distance sensor located? I unplugged the oil pressure gauge and plugged it back in and now it’s working, I was told that one of the fusible links on the driver side fender was for the speedometer and could’ve burnt up from the fire.

 

[AnonEd]

On my 92 manual distance sensor is near the t’case rear output. I couldn’t see any fusible link for the speedo, only the wires noted above. I’ll try later to get an image from the manual, but you may be able to download them online.

 

[AnonEd]

These might be helpful

 

[camron]

These might be helpful

View attachment 127344

View attachment 127345

Thank you this did help a lot, I will let y’all know if I get it fixed and what was the problem.

 

[camron]

These might be helpful

View attachment 127344

View attachment 127345

I followed the distance sensor wire all the way from the computer to everything it goes to and I couldn’t find anything wrong, I tried to follow the crank position sensors but I can’t seem to find where it goes.

 

[AnonEd]

On mine it’s a plug just below #1 valve cover, almost straight down behind belts to approx 11 o’clock viewing crank from front...not easy to see. A couple more images for starter circuit and fusible links.