72 C20 No Electric

[jeff71]

I have no electric at all on a 1972 Chevy C20. Unfortunately, I hooked a battery charger up the wrong way for about 5 minutes. It did start and run several times after I corrected the problem and finished charging the battery, but after a few successful starts, it went dead. I have followed the steps provided by Zeke's Garage on an earlier post called "No Electric" from 2011. This included: I have tested for voltage at the battery, side junction, positive post on the alternator and the block on the firewall. I have voltage on all those. I think this proves that there is not a fusible link that has gone bad. Let me know if that is wrong. Next, I tested the power wire coming into the cab from that firewall block, and then I tested voltage at the power wire going into the ignition switch. For these checks in the cab, I used the dimmer switch on the floor as the ground. Those two checks also provided voltage. (I have a new ignition switch.) Next, I thought I would check the ignition wire for voltage with the switch set to crank the starter (pink wire). I took out the ignition fuse from the fuse box, clipped my positive from my tester to where the pink wire comes into the fuse box, and clipped my ground from the tester to the dimmer switch. When I turn the ignition switch to the cranking position I get no voltage and the tester goes into continuity mode (which is what it was designed to do if there is no voltage). I do get a beep, so there is continuity. I am wondering now what my next step should be. I think if everything was working properly, I would have gotten a voltage reading and that makes me think that I need to inspect that pink wire, which means pulling out the dash panel to get to its full length. But I would like the opinion of someone with better knowledge than myself.

[RustyPile]

With the ignition switch in the START position, check for voltage on the purple wire at the switch (this wire carries voltage to the "S" terminal on the starter solenoid). If you have an automatic transmission, from the switch the purple wire goes to the neutral safety switch, then to the solenoid..

[jeff71]

Hi RustyPile, thanks for the guidance. I got back to work on that truck this last weekend. This time there was no voltage at the ignition, so retraced my steps under the hood and did not have voltage anywhere else that I previously mentioned except at the battery and the block on the passenger fender, so cut the tape and started looking for the fusible link and sure enough it was severed. Not sure why I had voltage on the tester before, but it was lower than ten volts, so maybe that was an indication that went over my head. I will be replacing the link and see if it fires up.

[RustyPile]

Originally Posted by jeff71

Hi RustyPile, thanks for the guidance. I got back to work on that truck this last weekend. This time there was no voltage at the ignition, so retraced my steps under the hood and did not have voltage anywhere else that I previously mentioned except at the battery and the block on the passenger fender, so cut the tape and started looking for the fusible link and sure enough it was severed. Not sure why I had voltage on the tester before, but it was lower than ten volts, so maybe that was an indication that went over my head. I will be replacing the link and see if it fires up.

I'm glad you found the problem, I was beginning to wonder what happened to you. When you replace the fuse link, make certain it's the correct gauge. Also, be aware that the link's conductor material (alloy) cannot be soldered, solder simply will not "stick".. Use a butt splice connector and crimp it very solidly., then cover the splice area with heat shrink.

After you get the engine running, check the charging system for full output. Sometimes reverse polarity voltage can damage the components.

['68OrangeSunshine]

With a reverse polarity charge, I would suspect a fried Regulator. It's either in the Alternator or the Voltage Regulator if external.

[71CHEVYSHORTBED402]

Originally Posted by '68OrangeSunshine

With a reverse polarity charge, I would suspect a fried Regulator. It's either in the Alternator or the Voltage Regulator if external.

Yep, my regulator failed off exactly that off a snip of time in reverse. Good idea to replace fuses mentioned too. Come to think of it, may have messed up my light switch someplace too, I only remember it had a short, and seems the mech...disconnected it

['68OrangeSunshine]

Headlight switches have a circuit breaker inside -- if I'm not mistaken. They can come back if they cool down. But if there's a short they are not expensive and easily replaced.

Unlike the old T3 tungsten filament headlights, LEDs are sensitive to polarity. If you had those, check them out for failures.

Are you running the original vintage style Alternator with External Voltage Regulator?