Once again, I'm trying to fix some issues on my '84 Camaro. This is two different problems, one of which affects every power accessory in the car.

1: Every time I use a powered accessory, the engine bogs hard and the ammeter immediately drops into the negatives and stays there until I come off of idle. This goes for the heated rear window, electric cooling fan, and radio so far. Radio signal is also very unstable; it rapidly goes from loud to quiet and back again. This is a newer radio, and it was wired up by the previous owner. The guy's an electrician and owns his own business so I assume he knew what he was doing. The electric fan also doesn't come on automatically, I have to switch the A/C on to get it to activate, unless you turn the car off and back on again. I'm thinking that's a problem with the sender/sensor for the fan (assuming that's separate from the gauge sender) but it seems odd that it would work automatically only once after the key was turned.

2: The tachometer stopped working about 20 minutes after I purchased the car. No idea why but from what I saw before it died, the car idled at around 750 rpm.