Engine bay rewire
 

So I have an early '79 SA, with the original 12a and everything, I've come into some wiring problems. The car will start right up but when I make any adjustments to the wiring or anything in the engine bay. It blows the 20amp engine fuse. I take the key out, and put another fuse and It doesnt blow right away. I can even prime the car for startup and it starts and runs fine a little quirky but I had just been doing carb adjustments and it hasn't run for long enough to adjust it yet. Anyways I'll start her up but when I go to adjust the carb the fuse blows? Im sure its the wiring since it is quite old and has been driving in Arizona heat all its life. My question is how tough is it to rewire the engine wiring like from the connectors and beyond. Also to add in when I took out the intake manifold this last time the b connector on my Alt broke and I had to replace it and when I prime the car to start without it plugged in and connect it it blows the 20amp fuse? Idk that's why I gotta ask I'm baffled. And I've read both the Haynes and factory Mazda book but I've gotten nothing from it.

Maybe you could be a little more clear... are you talking about fuse in underdash fusebox,or underhood fuselink? The alt output wire(Batt.terminal) blows fuse when you connect it to alternator,car shuts off? It shouldn't blow the fuse when you're connecting it-why are you connecting it after starting car? Leave it disconnected and tape off terminal so it won't touch anything and short. Start car,does it stay running til you turn it off? Start and warm up and adjust carb so it can stay running reliably. Shut it off.
Do you have a voltmeter? Ground negative lead of meter at battery negative terminal. Touch positive lead to batt. positive,note the reading,should be 12+volts. Untape alternator batt.terminal for wiring you taped up earlier and check for voltage there,should be very close if not exact same as battery voltage. If not,do not hook up to alternator.
Do this and post back your results,can give further guidance after posting what is found.

alright ill try that man. and it blows the underdash fuse the 20amp one. It blows the fuse even with the car not running like ill turn the key to on and the fuel pump will go and start ticking, but ill leave the alt disconnected at the b terminal. Before even starting the car cause i dont want to drain the battery ill connect the b terminal, but when I connect it sometimes it blows the fuse and no more fuel pump and all the other systems. sometimes it doesnt blow the fuse and itll be just fine. i start it and let it warm up, and the carb isnt badly adjusted it just needs the little fine tuning. when i try to even do the fine tuning itll just turn off randomly and the fuse will be blown. if i leave her alone though she runs just fine? its when i try to adjust anything yanno. and when it does blow its back to that whole sometimes it blows with the b terminal connected and sometimes it doesnt? idk im baffled, and ill do that which you said and ill get back to you shortly.:icon_tup:

Sounds like a wiring harness gremlin. Those can be a pain in the a$$ to track down. Try to pay attention to what you touch when fooling with the carb when it happens. I bet there is short or something shorting as you lean in to adjust the carb thats doing.

There might be a short somewhere near the alternator, since that has constant 12v power to the terminal on the backside. I'd watch out for that post and make sure you're not contacting that when digging around in there. Then make doubly sure to take note of anything you're touching and report back with pictures of where you think the short could be occurring and someone here can easily read the wiring diagram for you and give you a better idea.