I have a very weird electrical problem on a 78 J10 258.
Let me rule out what it isn't by listing what I've done:
Voltmeter swap / alternator charging circuit rewire, HEI distributor, Good battery, good starter, new starter solenoid, GROUNDS ARE ALL GOOD REDONE OR ADDED, New + battery cable (with soldered eyelets), New ignition switch
Now let me explain whats going on.
Was driving the truck daily with no issues. Parked it during December & January then it wouldn't start. Key wouldn't do anything. Started tinkering with it and noticed there was no headlights, no horn, no wipers, no power to anything. I know grounds are a huge deal so even after redoing all my ground connections i took a jumper cable from the - post and clamped it to various spots on the body & frame. Still no change. I have 12 volts from battery to firewall plug at the red and yellow main feeds. Inside the cab I initially have 12v to the ammeter terminals. With a voltmeter hooked up to these wires and i try to crank the engine as soon as i crank the key volts drop to 3v and then slowly climb back up to 12 volts. I can visually watch the headlights slowly come on and get brighter if i leave them on after trying to start. Volt meter hooked up to the battery with same procedure it reads a constant 12.2V no change when cycling the key. I've also tried unplugging nearly every accessory to try to isolate the issue but still no change.
I am able to turn the key into run position then jump the solenoid with cables and engine fires up. Once it fires up I have 100% power to everything (headlights, horn, wipers, etc). I shut it off then its back to no power again.
It cant be the fusible link because 1) I've tested good continuity and 2) it is in the yellow main feed which doesn't go to anything with key off. the red main wire goes to the wire junction and powers everything when off.
I've exhausted nearly possibility and am very grateful for any advice!
Let me rule out what it isn't by listing what I've done:
Voltmeter swap / alternator charging circuit rewire, HEI distributor, Good battery, good starter, new starter solenoid, GROUNDS ARE ALL GOOD REDONE OR ADDED, New + battery cable (with soldered eyelets), New ignition switch
Now let me explain whats going on.
Was driving the truck daily with no issues. Parked it during December & January then it wouldn't start. Key wouldn't do anything. Started tinkering with it and noticed there was no headlights, no horn, no wipers, no power to anything. I know grounds are a huge deal so even after redoing all my ground connections i took a jumper cable from the - post and clamped it to various spots on the body & frame. Still no change. I have 12 volts from battery to firewall plug at the red and yellow main feeds. Inside the cab I initially have 12v to the ammeter terminals. With a voltmeter hooked up to these wires and i try to crank the engine as soon as i crank the key volts drop to 3v and then slowly climb back up to 12 volts. I can visually watch the headlights slowly come on and get brighter if i leave them on after trying to start. Volt meter hooked up to the battery with same procedure it reads a constant 12.2V no change when cycling the key. I've also tried unplugging nearly every accessory to try to isolate the issue but still no change.
I am able to turn the key into run position then jump the solenoid with cables and engine fires up. Once it fires up I have 100% power to everything (headlights, horn, wipers, etc). I shut it off then its back to no power again.
It cant be the fusible link because 1) I've tested good continuity and 2) it is in the yellow main feed which doesn't go to anything with key off. the red main wire goes to the wire junction and powers everything when off.
I've exhausted nearly possibility and am very grateful for any advice!
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