No Electrical Power ??!!??!!??

[72restorationvirgin]

Ok I'll try to make this as short as I can. I looked up several other threads but I'm no electrical person and know minimal. I've been working on my 72 C20 replacing the dash pad, and doing some stuff with my instrument bezel.

Everything was good and I had power after I put everything back together. My lights were on and I went to start it and everything dimmed down and blacked out. I went to check the battery terminals and tighted them up good. Started right up and had all lights.

A few weeks later I did the same thing. I had my head lights, dome light, ect. I went to start it and it lost all power again. I checked the terminals again and everying was good. I cleaned all the terminals. I cut the positive wire and remounted it to the clamp so everything was clean. Still nothing. I checked the power to the starter and that was good.

I checked the ohms and continuity between both the negative cable to the engine block and the positve cable to the starter. Everything still good!. I checked the small fuse link between the postive cable and cleaned the connection to the passenger side fenderwell. Still nothing!!!!

Today I went and bought a new battery. They tested it but couldn't get a connection on the negative terminal so they said I might have something internally broken. Cool... So I put it in still nothing!!!!!!!!! I checked the wiring to the fuse box, ignition and everything is good. I checked the voltage regulator, unplugged stuff cleaned everything up. I"m at a lost for words. What am I missing?????

[VetteVet]

There's only 2 wires that feed the whole truck, actually three if you include the fusible link from the battery positive cable to the fender post. There's a red 12 gauge wire from that post across the radiator in the harness That goes to a 4 way junction which is soldered with three or four other wires, and from that junction is the other feed wire which goes up into the firewall block and feeds everything in the cab.

A poor connection anywhere in this circuit will give the symptoms you have.
The fuaible link wires have been known to blow all but a couple of wires and create a poor connection to the fender post terminal. Same thing with the red wire across the radiator in the harness. The soldered connection may be corroded. Most likely the problem is in the firewall block connection. If this happens again try wiggling the wires in the block to see if the lights come on.

Here's the block.




Here's the inside terminals that get corroded.




Here's the diagram that shows the red wires. The circled fuses are for the battery gauge if you have the gauge dash. The wire that says SHUNT is the connector wire from the fusible link to the four way connection. It'll be taped up in the main harness.

The other side of the equation is the ground wire from the engine block to the frame in addition to the negative battery cable to the block. You should have one from the back of the engine to the cab as well.

[72restorationvirgin]

Thanks Vett. I thought it may be there because yesterday I moved some wires around there and the dome light came back on however when I turned the key it went out again. I tried wiggling the wires but no luck. Is there something I can replace there or do you pretty much need to replace the wire harness??
Posted via Mobile Device

[VetteVet]

If It's still out then run a 12 gauge wire from the battery positive or the back of the alternator over the left fender and through the open door to the ignition unfused terminal on the fuse box and see if you get power. If so then you should take the firewall plug off and clean out the red wire contacts and any others that look corroded. If the headlights and park lights and front turns work as well as the horn, then it's definitely the red wire. The red wire on the horn relay harness plug is a good place to jumper to since it is connected to the red wire that comes through the fire wall plug.
If the wires all look ok then I wouldn't spend $400 for a new harness. If you have a bunch of cut spliced wires that are cracked and crappy looking then it is worthwhile.


Here's a diagram that shows the red wire after it comes through the firewall plug and you can see how it tees and makes power connections to the rest of the cab. Follow it and you can see how it feeds the horn relay and the fuse panel. On the top of the diagram it goes to the key switch.



This one shows the red wire powering the light switch and the key switch.


I assume you know that if you take the bolt out of the center of the firewall block you can separate it from the inner half. Be careful because the plate nut on the inside of the firewall will turn if the threads are corroded on the bolt. You can take the two small screws out of the fuse panel corners and lower it down where you can see the bolt threads and you can soak them with penetrant. The nut is only held in by two ears and the rubber it sits in so it is easy to strip.

[72restorationvirgin]

Vette,

Ok I got all excited because I starting playing with the red power wire that fed from the passenger side fender and across the radiator (see attached pics). There was an old splice and I pushed them hard together and got lights. So I took the tape off and put a new plug on and retapped it up. I had lights and dome light. I didn't have wipers and only one gauge light came on. I did replace all the gauge lights put I used the same lights for them 194's and 168's. I made sure the plug was tight when I plugged the instrument panel back in.

Then I tried to start the truck and the dome light went dim again however when I turned the key back/off the dome light and head lights came back to normal. Then I smelled burning plastic and the new tape I put on the splice was melting. I'm assuming it's getting an overload from something???? The only other wires I missed with were when I cut and reclamped the postive terminal. Any ideas??

[72restorationvirgin]

Oh and when I pulled apart the old wires to redo them it looked like they were also soldered together. Would that make a difference or did the PO just do that for a better connection?
Posted via Mobile Device

[72restorationvirgin]

Sorry for the multiple replies... Vette look at my second pic with the battery. In the upper left corner by the neg cable there's a wire going down with a fusable 20v glass fuse that was blown. Would that cause the wire to get hot since they are running off the same power? I'm hoping after I buy a new fuse tomorrow I'll be good..
Posted via Mobile Device

[72restorationvirgin]

Well I finally figured it out!!! After the new battery, some new wiring, new in line fuse links and new in line fuses it was all my fault to begin with. It turns out somehow, no idea how, when I was putting my new dash pad in one of the dash pad nuts spliced into my main red power wire shorting it out!!!! Loosened the bolt up fixed the wire and shazam! Guess I'll look a little closer next time.
Posted via Mobile Device
Posted via Mobile Device