Voltage spikes and suspected alternator issues

[bfloyd]

Got a weird thing going on with my electrical system. Coming home from DMC Midwest on Thursday night, my voltage meter was running high - up into the 16-17 volt range. Turning on the AC would make the voltage meter swing the opposite direction below 12 volts, everything in the car dimmed, radio quit working, dash lights dimmed, headlights dimmed, and the battery light came on on the dashboard. I suspected the voltage regulator in the alternator was going out. The car finally died at a rest area along the Interstate and I ended up getting towed the rest of the way home.

Pulled the alternator this morning and took it to a local auto parts store to swap out. They tested the alternator and its perfectly fine. Passed all of the tests on their machine.

I have converted all of the gauge cluster lights to LED, but did leave the battery light as incandescent, sooN don't think its a charging issue.

My alternator is not a DMC alternator, but a cross reference to a Cadillac Eldorado. Its worked perfectly fine for the last 4 years. It wasn't my choice, as the previous owner swapped it out and modified the wiring at the alternator. In 2015, I just replaced what he had in there with another just like it.

Where do I look now?

[David T]

Have the battery recharged and tested then start checking all of the "big" connections between the battery and the alternator.

[Bitsyncmaster]

A bad connection to the battery will react like that. Had the same problem in a boat this summer. Volt gauge showed pegged at 20 volts but engine was running fine. Hit the power tilt and it killed the engine. Turned out the battery cable fell off the battery.

[Ron]

+1 both Daves...

Check both ends of both battery cables and large brown wires at the main stater terminal. Make sure the battery light comes on with KOEO...since an Eldorado alternator (#7127-X or 10SI) may not have a self-exciting voltage regulator in it (If not, it would only put out after a high rev...).

[bfloyd]

Took the battery in and had it tested. Its perfectly fine. Cables were tight on the battery when I removed them. Checked the wires at the starter, and all seems tight there as well. I went ahead and replaced the alternator with a new one, but haven't got the chance to install it yet.

Only other place I can think of might be the battery switch. If the internals of that switch are wearing out, that could be a likely culprit.

[David T]

You must also check all the ground connections between the battery and the frame.

[DMC-81]

Took the battery in and had it tested. Its perfectly fine. Cables were tight on the battery when I removed them. Checked the wires at the starter, and all seems tight there as well. I went ahead and replaced the alternator with a new one, but haven't got the chance to install it yet.

Only other place I can think of might be the battery switch. If the internals of that switch are wearing out, that could be a likely culprit.

Agreed. I would check that out. Maybe bypass it to test. I had a no start condition and or stalling condition a couple times in my garage and the culprit was a battery cutoff switch that wasn't completely tight. Accessory lights worked and starter would work, but it wouldn't fire, or would stall after a minute or so of idling.