Just having voltage doesn't mean much. An almost dead battery can have 12v.

If the cables or corrosion between the post and battery clamp is bad then NO AMPS can get thru. AMPS are what makes the starter turn or the lights work.

Volts without AMPS equals failure.

Jumping a dead battery, without allowing it time to charge, draws amps from what is needed to turn the starter correctly; putting a strain on everything else. This can lead to premature failure of the starter, solenoid, cables, and alt.

Start with a good fully charged battery, clean posts and clamps, new cables(in your case), clean solid grounds
and then you can evaluate your charging system.
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well the alt is brand new, so if i replace everything and still get nothing, im gonna be mad haha

 

had similar prob / starter was drawing to much and cables were brittle and cracked - so when moved they had no current, went longer and heavier ran thru motor mount easy bend to starter- and new starter . still have small battery came with the 78
ps -- make shure shifter is in park all the way to enshure nutrual switch is active.
mine jumped to life again

 

Replaced the solenoid and positive cables, and wire brushed the terminals and bam good as new

 

good glad you got it fixed, sounds like you should have a nice healthy electrical system now.

 

Everything seems happy. Headlights still pulse though.

 

the stock headlight harness is pretty weak and if I remember right, does not use a relay. Wouldn't be a bad idea to check the grounds and the connections for corrosion, but there are upgraded headlight harness available, or if you are handy you can just wire in a bosch relay. Does your voltage spike while running? If your regulator isn't functioning properly, it can also pulse the voltage. I had a suzuki I inherited and the headlights always pulsed, if you put a multimeter in the cigarette lighter it would go 13-14.5, 13-14.5, etc, I suspected the regulator but everything worked fine, just the headlights pulsed brighter with the voltage spikes. I never bothered to fix it, and it pooped the tranny eventually in an unrelated incident.