Help with melted wiring on headlight switch

[mrk5]

I was poking around behind the dash and found some melted wiring. Those that have followed my crew cab build will know I've found lots of hinky previous owner wiring and apparently this may have been the result.

Here's the first wiring in question:

This one appears to be a brown wire that is connected at the headlight switch with another brown wire. I drew a green line next to both lengths of the wire. One brown wire ends in a plug that was not connected to anything. The other brown wire was running under the top of the dash and molded with an orange wire. They were both, orange and brown, cut by a previous owner and deadheaded. (Don't know if they were supposed to be molded together or if they melted together.) The orange wire was connected to the top of the fuse block with a factory looking connector.

According the wiring diagram I have, the brown wire is supposed to be for tail/park lamp but my tail lights have been working even though both brown wires were disconnected.

The melted brown wire only had power with the headlights on, but I didn't check the brown wire with the plug at the end.

The other wire is missing all of its insulation. It shares a connection on the headlight switch with an orange wire, so I'm assuming it was also orange.

Both orange wires disappear into the wiring harness. The wiring diagram says this would be a wire from the fuse block, at least 1 wire would be. Then I'm assuming the other wire goes to some sort of load but my wiring diagram doesn't say (at least not that I've found).

The wire with no insulation left was hot all the time.

Unmolested photos:

I'm wondering if anyone has an idea what these wires are for. I feel like the wiring diagram I have is only giving me half the story for the headlight switch wiring as at least these 2 connections have 2 wires. And neither brown wire was connected so I don't know what it was even accomplishing.

My hope would be that I can just cut the wire with no insulation left and kill the power to it. At least until I can get the time to trace it out and replace it. I'm assuming it must do something important.

Would appreciate a good drawing or diagram that give the complete story for headlight switch. Or at least a good idea what these wires were for.

Thanks in advance.

 

[ktmoutfront]

What year is your truck? I have a couple of books for the harnesses.

 

[diesel4me]

This is for an '83 C/K truck but it should be close or the same as most 73-87's...(if you can read it!)..sorry its upside down and blurry,my scanner doesn't do too good with a book stuffed in it..the light switch is in the upper LH corner..

 

[mrk5]

What year is your truck? I have a couple of books for the harnesses.

89 R3500

This is for an '83 C/K truck but it should be close or the same as most 73-87's...(if you can read it!)..sorry its upside down and blurry,my scanner doesn't do too good with a book stuffed in it..the light switch is in the upper LH corner..

I'll check it out once I'm at my desk and have a better monitor to view it on. From what I can see from my mobile it looks like it should be helpful.

 

[ktmoutfront]

87 is as close as I can get.

Orange - 240c-Q36 shows going int the fuse block for marker lights

Brown - 9c-d24 shows to be going to the dimmer switch and the radio light. 2 wires.

 

[mrk5]

The brown wire makes sense. I'll bet that orange lead it was molded with went to the radio for power. I'll bet he just cut the wires when he pulled the factory radio. The guy I bought it from bragged about putting some badass aftermarket stereo in the truck.

When I got the truck the instrument lights didn't work. Found the fuse blown. I bet that happened in the same event that caused the insulation on that wire to boil. The end he cut probably contacted metal.

On the orange wire, the side of the wire that is melted must be the wiring coming from the fuse block. Then the other wire would be going out to the marker lights. If that's true, at least I won't have to trace that orange wire back far. Going to be a bit of a bitch to wire the new wire to the headlight switch tho.

Not sure what happened to the orange wire. But the wiring at the headlight switch was a mess and it's possible that the brown wire melting also melted through the orange wire as well and caused it to short out.

There was also the issue of the tach the PO had wired that had 12V power being supplied by a splice into one of the wires for the gauge cluster lights. That may have contributed to the chaos as well. Hell who knows what other crap he did that he actually had to fix himself. Although that's a scary thought too.

 

[ktmoutfront]

http://www.ezwiring.com/wiring_harness.html

 

[mrk5]

I've been tempted to do that since I found the first craptastic wiring job by the PO.

 

[paratrooper307]

The light switch takes the load in this system, so cooked wires are a common occurrence. Prevent this from happening in the future by wiring in some relays or getting the LMC light harness. Nothing is more aggravating than bad wiring, since it can lead you on all kinds of wild goose chases to correct problems.

 

[mrk5]

I'm guessing it was caused by the cut end of the brown wire touching bare metal and shorting out. That melted through the orange wire and shorted it out as well.

The orange wire that is melted has to be coming from the fuse block because after I cut it from the headlight switch it still had power. I think it shorted out from the brown wire because if it had been a short on the load side that wiring would have been toasted as well.

 

[ktmoutfront]

The orange wire is the fused feed to the switch.

 

[mrk5]

I ordered a wiring diagram manual for my truck on ebay and it is very useful.

Here's the diagram with the orange wire in question:



The wire with no insulation left is from the fuse block as I suspected. The other orange wire on the same terminal is for courtesy and dome lights. This truck doesn't have a dome light and now I know why the light under the dash doesn't work either since it was cut.

The brown wire is for radio clock (which I don't have) and cab roof marker lights which I don't have explaining the unused plug (the plug is shown in the drawing below).



Fixed the wiring this weekend. I cheated and just pulled a new wire to replace the melted orange wire. I had never removed a headlight switch before so I had to look that up. Pull the knob out, push in the metal button indicated below, and then pull the knob and it comes out with the shaft.



It does take some fiddling to get it out; just long enough to be just about ready to give up.

Then spin off the "nut" indicated below.



The wiring connector unplugs from the switch without any special steps. To remove the bad wire, you must access it from this side.



I have a tool that will allow the connector to be removed.



On the picture below you can see the little tine that sticks up and holds the connector in the plug housing.



The tool is inserted to push that tine down allowing the plug to be pull out.

When I did a bunch of wiring in my K5 I found a type of plugs I really like. They are called Packard 56 connectors. By unplanned coincidence they are also the same type of connectors used these trucks. It has been very handy for repairing wiring and also changing wiring connectors.

The trick to this connector is that it has 2 wires. They do make special connectors for this purpose, but I don't have those. I've had good luck getting 2 wires to work in the standard connector.



Here's the old connector compared with the new.



And the new connector with the wiring.



Plugged it back in the electrical plug housing and everything is working good. I pulled the new power source from a battery connection on the fuse block. I added a 20A circuit breaker for protection; the original power source had a 20A fuse.

I just eliminated the brown wire from the plug since the stuff it powers isn't on my truck.