popping main fuse while cranking 84 GS
 

I went to go start my car after it was sitting for a while, and when I go to turn the key to "start" the main fuse pops. I have never had any problems with this before, and I am a little stumped. The main fuse will only pop when I turn the key to crank it. I can leave the car sitting on "ACC" or "on" all day long, and that main fuse will never pop. Is this a common problem?

If its only popping when your cranking then you are having a short after the load i.e. the ground is improperly grounded or your getting unwanted wire on wire connection causing an excessive draw.

in the case of a wire on wire connection what wires should I be looking at that would cause the main fuse to pop? Looking at the wiring diagram, I see that when the ignition switch is turned to start, it sends power to a B/Y wire that feeds to the starter solenoid. I disconnected this wire from the interior ignition switch in attempt to isolate the problem, and the main still pops when the key is turned to start. Could a bad ground cause the fuse to short like that?

do you have a stock ignition and alternator? Your issue is probably either something triggered at the "start" circuit, too much combined load when the start cicuit is triggered, or a bad ground in the circuit. Too verify this the easy way, find a place in the ignition swith wiring where you have a little slack and isolate the "hot on ignition" wire, cut there and try again. If it doesn't trip you know where to search. If it still trips, it's in the switch itself. Work your way through (powered at ignition) one at a time till it stops or you find a bad wire/ground.

Update
 

Thanks for the advice. When you said ignition, it triggered a thought in me to check the coils. So, I disconnected the both ignition coils (spade plugs and ring connectors and removed them from the car entirely. I went back to the car, and voila! No more popping main fuse. So, I have an MSD box with some accel coils, gonna go hook those up now. Thanks for all the help.

Congrats! Glad you got it worked out. ;)