wiring harness hot... ??

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lvshust

lvshust

Joined
Nov 22, 2009
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1978 FJ40 2F

so i was working on my rear harness and testing out the wires for the rear. got the back-up, running and brake lights all working...

this was done while the ignition was turned, i came back around after a few minutes and saw a slight bit of smoke and smelled something cooking...:mad:

the ignition switch connector was very hot and the rest of the harness back from there all the way to the passenger side and to the other side of the firewall was warm...

i have taken the harness out and searched for anything wrong. all wires appear to be in good shape... what next?...
:meh:
 
Last edited:
lvshust said:
1978 FJ40 2F

so i was working on my rear harness and testing out the wires fro the rear. got the back-up, running and brake lights all working...

this was done while the ignition was turned, i came back around after a few minutes and saw a slight bit of smoke and smelled something cooking...:mad:

the ignition switch connector was very hot and the rest of the harness back from there all the way to the passenger side and to the other side of the firewall was warm...

i have taken the harness out and searched for anything wrong. all wires appear to be in good shape... what next?...
:meh:
Click to expand...

Check your ground(s) for the rear section of the harness.
 
lvshust said:
i have taken the harness out and searched for anything wrong. all wires appear to be in good shape... what next?...
:meh:
Click to expand...

Turn the key on and find out which wire gets hot.

My guess would be the ignition wire to the coil as it is the only wire that is not fused. This would be especially likely if you are runing a "performance" coil or running a resistor type coil without a resistor.

The other less likely possibility would be a short on the key on side of the switch before the fuse block. It is unlikely to be anything shorted after the fuse block unless you have installed the wrong fuse with too high a rating. Normally a fuse would blow before the wire gets hot.
 
Pin_Head said:
Turn the key on and find out which wire gets hot.

My guess would be the ignition wire to the coil as it is the only wire that is not fused. This would be especially likely if you are runing a "performance" coil or running a resistor type coil without a resistor.

The other less likely possibility would be a short on the key on side of the switch before the fuse block. It is unlikely to be anything shorted after the fuse block unless you have installed the wrong fuse with too high a rating. Normally a fuse would blow before the wire gets hot.
Click to expand...

ok pin... i am hooking back up now... what do i do with the two W/B wires that i am supposed to hook up the the speedo cluster i do not have in yet... connect them for now?
 
White wires with black stripe are ground wires; probably for the bulbs in the instrument cluster. If they end in ring terminals, they problably go to a screw in the sheet metal somewhere near the end of the wire.
 
Make sure your fusible link is good. That is the wire that hooks to Positive terminal of the battery and supplies +B voltage to the whole system. It is quite common on 40’s to have be corroded and cut to the nub. It has an inline connector that connects to the loom and a ring terminal that connects to the battery. Grounds are very important too and common to be corroded, make sure you have good continuity from the battery Neg – to the frame, the tub, dash and the engine. This also helps with noise in Stereos, CB’s, and other audio related devices.
I do have a question.
Did you by chance add halogen backup lamps?

Caig Deoxit D5 works great for cleaning corroded connections.

Also Phantom intermittent connections can be corrected in the 40’s fuse block with a .22 cal barrel brush and Deoxit.
Disconnect the battery, remove fuse from fuse block and clean with the brush and spray.

Good luck Have fun..
 
yoyo... i have a fusible link coming from the positive lead... maybe it is the wrong size?

i believe i have a 14 gauge link on now...

i have a couple other sizes... 18 and 16...
IMG_0682.webp
IMG_0683.webp
 
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ok... i changed the fusible to 14 gauge...

i linked up the harness and spread apart so i could isolate the hot wire...

it is indeed the pink wire that is running the length of the harness and ends behind the fire wall into the engine bay and near the driver side panel on the inside... note the pictures below...

i cannot find a pink wire on any diagram...
IMG_0684.webp
IMG_0685.webp
 
OK it appears that the pink wire has been spliced to the BY wire presumably because the BY wire at some point fryed itself or broke inside the harness. The BY wire is always a power feed and on a 78 it feeds the ignition, the regulator, the Emissions computer, the VSV, and the fuse box.

Where does this pink wire actually go?
 
Coolerman said:
OK it appears that the pink wire has been spliced to the BY wire presumably because the BY wire at some point fryed itself or broke inside the harness. The BY wire is always a power feed and on a 78 it feeds the ignition, the regulator, the Emissions computer, the VSV, and the fuse box.

Where does this pink wire actually go?
Click to expand...

so this is the route of pinky...

drivers side, check out the union of these two wires, very different gauges?

it branches into three BY wires
-ignition switch
-fuse block
-fuse block
IMG_0692.webp
IMG_0685.webp
IMG_0687.webp
 
That appears to be some seriously screwed up, non-stock wiring. I would get a schematic diagram and try to make it like the factory originally intended.
 
Pin_Head said:
That appears to be some seriously screwed up, non-stock wiring. I would get a schematic diagram and try to make it like the factory originally intended.
Click to expand...

i would love to, but why did this car run for as long as it did on this setup?

the problems only started when i started the assembly process, i think it is on my error. the wires look ridiculous though...

i have a FSM and many diagrams, so off to the races...
 
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