Could a bad alternator cause gauges to stop working?
 

Just wondering if that could be the reason for my car's flakiness..

In all my years I've never heard of that.
I do know that these cars are very finicky when it comes to grounds.

Ok...thanks. The mystery continues.

a bad voltage regulator fried my tach (and my dme) on my '86 carrera. North Hollywood Speedometer fixed my tach for me and I was able to get my dme re-soldiered.

So, yes, it can happen, especially if the alternator's voltage regulator is failing and spiking high voltage through the electrical system.

Its not just my tach...all my gauges aren't working at the moment. They are spiking. Meaning, I turn the car on, and they pin out. My tach was weird...I was on a drive, and it became intermittent...then stopped working entirely.

What's your car's voltage when the engine's running. A bad voltage regulator will cause it to fluctuate into the high teens, which can fry stuff that's expecting low teen voltages. Your description sounds more to me like a grounding issue

My voltage running is around 11.8, which led us to believe the alternator wasn't doing anything.

11.8 VDC with engine running? you've your answer right there. Glad it's not an overvoltage condition.

Best,

Doyle

Which brings me back to the original question...could that cause gauge weirdness?

Check the grounds, probably the instruments have a common ground which must be disconnected.

Checked those, all fuses, and have done a ground test on the gauges. All checks out...

As Doyle said either your alt. or regulator is bad.
Should have around 12.8 volts or so running.
Don't know if this will fix your guages but i'd fix this first.

Michael,

You should have 13.5-14.5 V when the engine is running.

11.8 is too low with the engine OFF.

Your voltage regulator is toast.

I'll bet fixing that fixes everything.

I had a bad alternator and gauges were spooky, the wipers turned on by themselves, etc.

I don't know the extent of your electrical changes (you have a '69 with a 3.0 CIS, right?) I'm guessing you have the new VR that's integral with the alternator, behind the fan.

Your 69 would have originally had a separate VR on the left firewall by the CD ignition.