Cluster twitches bad

[1500z71]

My '93 cluster just started this today. It's kinda hard to explain so I'll try to put it in simple terms. On the interstate rolling around 70-75 I would turn the AC on and the rpms and speedo would go nuts. Speedo would twitch its way to 85+ and peg out, the rpms would read 2500-3500. I have true duels to 4in tips so I would know if I was screaming at 3500rpms, so this is obviously the cluster failing not the true reading. Turn off the AC and it reads normal but still slightly twitches. Blinkers and hazards would seem to make it twitch all over the board with no pattern, and finally as a test I turned the AC off, and rolled both windows down and held the button after they were down and the cluster glitched out again like I mentioned. What kind of electrical issue do I have? Would've got a video but my phone was dead.

 

[1500z71]

I don't want to cause permanent damage to it either, and I'm about to put a ton of interstate miles on it in the coming years.

 

[skylark]

It sounds like a ground issue. Usually the one from the battery to the body or one of several under the dash.

 

[1500z71]

It sounds like a ground issue. Usually the one from the battery to the body or one of several under the dash.

Thank you sir. How might I go about checking grounds? Like how do you tell if they're bad?

 

[1500z71]

Here's a video of what it actually looks like:

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[1500z71]

I tried the ground from the negative battery cable that goes directly to the fender to no avail

 

[Justin S]

Might be a different ground for the cluster, i've had a couple that did that, but never cared to fix it haha

 

[1500z71]

Might be a different ground for the cluster, i've had a couple that did that, but never cared to fix it haha

Well there's nothing bad about it except since I'm out of high school now I drive interstate 30 minutes to work and then this fall i'll be making four hour interstate trips. Shocker it goes out when I really start using it for trips Think it's a ground under the dash?

 

[Justin S]

I wonder if there is a shared ground to heater control and the cluster. Kind of sounds like the a.c. is backfeeding to the gauges because the connection is poor.

 

[Justin S]

And yes, it would be in the dash somewhere. Possibly behind the radio, might have to follow the harness and see where the black wires run