Not quite a dumpster fire, but a wire fire

[thedudeabides86]

Soooooo, I learned a lesson last night. Disconnect the battery whilst working on things, when applicable. I installed a cigarette lighter from LMC last fall to charge the phone when I was driving. I disconnected the lighter cable to work on the heater assembly last night when all of the sudden I bumped the wire which sparked on the back of the lighter assembly. After a few seconds it had fused together and I got up to disconnect the battery. In the time it took to grab a 3/8 wrench and disconnect the battery, the lighter wire had burned up from the fuse box up toward the cluster under the dash. Hopefully, it didn’t melt any other wires behind the cluster but it did melt the radio wire, which, the radio hadn’t worked anyway. I cut out the bad wires and found a wire under the hood in the engine compartment that melted as well, but I’m not sure what it is or where it goes. I reconnected the battery and tried the headlights which was okay, but I haven’t fired it up yet. Anyone have any input as to what trouble this might have caused? The pictures posted are of the engine compartment and the wire coming off the fusible link (if that’s the right term?) on the side of the fender. Thanks for reading.

[zosoppp]

It sort of looks like the fusible link is the wire between the underhood junction block and the big yellowed rubber looking tube at the end of the red wire from the other side of the engine bay.

My understanding was that usually the red wire terminated at the block with a ring terminal, and the fusible link went between that block (with a ring terminal) and then was crimped to the smaller wire from the positive terminal clamp.

The fusible link wire is supposed to do what it did there, (special insulation) and it should be smaller (4 higher AWG number).

When you make up a new lighter wire (12 AWG RED) put an inline fuse holder (25A at most) at the fuse panel end of the wire to prevent that in future. If you have the original fuse panel there is an existing UNFUSED tap for the cigar lighter terminal.

[rpmerf]

Lighters typically get their own 10 amp fuse. I have a 30 amp between the battery and first junction. Only time it blew was when my voltage regulator died.

[franken]

You should have a fusible link between the battery and the junction block on the fender, which is most likely why this happened. You have a big red wire between the yellow butt connector and the junction block, so the wire from the other side of the junction to the firewall connector fried.
Now I see almost the same thing is in post #2--doh!

[toolboxchev]

Burned Spaghetti sucks. Trace those lines and pull the tape all the way or you will be asking for more problems down the road.

I have been chasing my elec. demons for quite some time now. I have just reconditioned a cab harness due to heater and ignition switch issues for the last week.

Its Snowing now and without a shop I'm taking a nap.

[68 P.O.S.]

I personally would get a new harness. If you want to keep it completely stock, you can purchase the harness in sections (engine harness, lighting harness, etc.) so you don't have to buy it all at once.

[thedudeabides86]

I've been looking into doing a complete rewire of the whole truck, but I have a wife and kids. The wire that fried, a coworker mentioned that might feed the fuse box under the steering column. Can I just cut out the fried section and splice in a new chunk of wire or is it best to just replace the whole run? I'm not a wire guy, but I can learn quick. Is there anything I can do as far as a tester for long runs of wire? I envision a flashing beacon on one end of the wire while I put a small tester on the other end to make sure I have a good run? Does it make sense to change a single wire at a time? Thanks for all the input guys.

[68 P.O.S.]

I hear you with the wife & kids; I'm in the same boat and it takes forever to get anything done with that budget lol. I rewired my truck with an AAW harness. I've used a Painless before too. They're both great harnesses. If you want to keep it stock, go with M&H. You can piecemeal their harnesses as well. Looks like you need the lighting harness to start with.

[jabborabbo]

My ‘67 GMC didn’t come with a lighter, so I put one in...I also put a fuse in the lighter circuit (12 gauge wire) since there wasn’t one, so I wouldn’t burn up the wiring in case something screwed up. Fuses are wonderful protection!

[dmjlambert]

I am concerned about why your fusible link wire did not burn up and disconnect the circuit. It should have done that before the 12 gauge wiring in your truck burned up. That is the purpose of the fusible link. The fusible link is that section of wire near your battery that has the burned insulation on it. It is supposed to be 16 gauge wire. You can buy a small section of it at auto parts stores in the electric section. It is usually grey in color and says on the package 16 gauge. It burns up first, to prevent burn up of your 12 gauge big red wire that goes into the cab through the firewall connector. On my truck, the cig lighter wire is also 12 gauge, and it is not fused and connects to the CIG connector on the fuse panel. Because it is 12 gauge, it should in theory be protected by my fusible link wire near my battery.

Thank you for posting your lesson learned. I don't always disconnect my battery when I should, and this same thing could have easily happened to me. So, I am glad to have the warning from you to remind me to behave properly. Something that I believe not everybody is aware of is when you disconnect the battery you should always disconnect the negative terminal first, and when reconnecting the battery, connect the negative terminal last. If I'm just temporarily disconnecting and leaving the battery in the truck, I don't disconnect the positive terminal, but I do like to cover the negative terminal with something plastic or rubber.

[toolboxchev]

Originally Posted by 68 P.O.S.

I personally would get a new harness. If you want to keep it completely stock, you can purchase the harness in sections (engine harness, lighting harness, etc.) so you don't have to buy it all at once.

I appreciate it, got a rebuilt harness in last night. All Lighting is working. Now to get that starter in today's Snowapoolloza!

Built, not Bought is my motto for now, I am OLE SKOOL.

[HO455]

Originally Posted by thedudeabides86

I've been looking into doing a complete rewire of the whole truck, but I have a wife and kids. The wire that fried, a coworker mentioned that might feed the fuse box under the steering column. Can I just cut out the fried section and splice in a new chunk of wire or is it best to just replace the whole run? I'm not a wire guy, but I can learn quick. Is there anything I can do as far as a tester for long runs of wire? I envision a flashing beacon on one end of the wire while I put a small tester on the other end to make sure I have a good run? Does it make sense to change a single wire at a time? Thanks for all the input guys.

The wire that melted should be the wire that connects the battery to the junction/splice near the horn on the drivers side (blue arrow). The splice joins the alternator output with the battery and the feed to the fuse panel. The part that melted looks to be the fusible link to repair it you can purchase a new one of the same gauge and solder it in as long as the rest of the wire looks undamaged. That being said from the photos your harness looks to have fairly modified at some point.
If you want some more information on the splice location or fusible links see the link and scroll down to post 468 to start.

https://67-72chevytrucks.com/vboard/...698377&page=19

[dmjlambert]

HO455 It looks like you used thicker than stock wires in your truck and you found 12 gauge fusible link at NAPA to go with it. I think what thedudeabides86 will need is 16 gauge fusible link wire. Do you agree?

On your truck's wiring you want the fusible link to protect whatever is the thinest unfused wiring. So if your thicker than stock wire that goes across the top of the radiator and past the alternator to the cab joins with 12 gauge wires under the dash to go to places such as the ignition switch, fuse panel, horn and horn relay, and headlight switch, then you will still want a 16 gauge fusible link at the battery.

[HO455]

HO455 It looks like you used thicker than stock wires in your truck and you found 12 gauge fusible link at NAPA to go with it. I think what thedudeabides86 will need is 16 gauge fusible link wire. Do you agree? Yes.