Real Fiero Tech

Noticed my battery voltage was dropping. Verified with a vom and sho nuff the battery was not seeing 13.5 or more volts when running. Battery voltage was steadily going down.

I tested the alt while the car was running by using a vom and putting the pos lead on the back of the alt and the neg lead on the neg post of the battery.

Voltage was under 12 volts. I figured the alt was bad. I got one from autozone and still the same problem. Tested with vom off the back of the alt and still not 13.5 or more volts. Voltage of alternator output with vom, tests exactly what the battery tests at when the vom leads are placed on the neg and pos battery cables

Both alts test good when taken to autozone and spun on their machine.

Ideas? Could a bad ground do this?

bad engine ground would be my first guess. check to make sure it's clean and tight on both ends.

Ditto. Sounds like a ground problem. Also check the body ground right below the battery. Mine had gotten rusty and the stock screw didn't have enough bite in the edges of the hole. I upsized the screw and everything was fine.

According to wire diagram two red wires run to the battery junction box from the alternator. I verified this to be true. The two are spliced right near the alt.

I checked continuity with my vom and I got a good reading for both wires pre and post splice and through the fusible link.

I then checked the continuity of the wire from the battery junction block that runs to the positive battery terminal. That checked out good.

I don't see how any other wires in the system could keep the battery from charging. Meaning if they are in the cabin or at the starter. Even if any of the other power wires are open or left unhooked the battery should be getting 13.5 volts from the alt right?

I verified the continuity of the ground wire from the battery to the engine block. That's good. I also verified continuity of the little ground wire to the chassis underneath the battery and that checked good.

For my next test I left both pos and neg wires discoed from the battery. I put my test light lead on the positive terminal of the battery and touched it to the chassis ground. No light. Pretty sure it shouldn't though cause the car technically has no earth ground.

a continuity test tells you almost nothing. you can have a good continuity test, but still have a high resistance ground. the charging circuit is fairly simple, you have the battery, which is attached to the alternator, the chassis, and the engine block, and the alternator, which is attached to the engine block and the battery. if your alternator is good, then you have a problem between the alternator and the battery, or the alternator and the engine (not likely) or the engine and the battery.

Took your advice Eric and checked resistance of all wires both power and ground. No high resistance.

I ended up cleaning the connectors at the battery junction block with some sandpaper and put it all back together. Fired it up and its charging again like normal. 13.2 at idle over 1500 rpm its over 14. Bad connection obviously in that area I think.

glad you were able to get it sorted out, it's always nice when it's an easy fix.