Gauges all read incorrectly and vary with signal

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Lgarretto

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Hi guys. Been trying to figure out why my gauges don't read right. None of them do. Except my speedo. It's close enough. My gas gauge reads off, reads over full when full, about a half tank when I have a half tank, but never goes any lower. My temp gauge reads about 250, but cools down with the engine. I've checked my temp. I'm not actually overheating at all. I have a 185 thermostat in it at the moment and a brand new radiator and I've checked it multiple times. It's dead on 185. My oil pressure usually reads 30psi and my amps read about 12. I have a good battery and alternator I know for sure. Both are only a couple months old. I haven't actually checked my oil pressure.
So. When I turn my blinkers on all three of those gauges, temp, amps, and oil, bounce back and forth with the turn signal clicking. Like a metronome. I have a tach wired in and an aftermarket radio. I know the secondary wire to the radio has no power to it. I had to splice a wire directly to the fuse.
I'm not sure where to start with the gauges. I think the gas may be a bad sending unit. And oil pressure may be right. But they shouldn't move with the turn signals. Anyone got any ideas?
 

someotherguy

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You've got a ground issue. Either some damaged wiring from previous work, or you tapped in somewhere incorrectly. I'd start with the gauge cluster ground at the metal tab where the diagnostic (ALDL) connector is mounted.

Model year and other info is generally helpful whenever asking questions instead of making people guess.

Richard
 

Lgarretto

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I can't be sure of course, which is why I am asking the question. But I don't think the issue is the cluster. I think it has to do with wiring. But idk where to start looking.
 

Lgarretto

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Oh I forgot to tell yall truck info. I apologize. I have an 89 swb with a 350 tbi and a 5 speed.
And I will go check the ground right now
 

Lgarretto

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OK well I will let yall know if that is the issue. There is a connecter for a wire that is bolted onto the right side of the obd port but it has been cut. Idk where it is now. There is a massive rats nest of jumbled up wiring underneath the dash. Whoever had the truck before me I have already deemed dumber than dirt from other issues I have fixed as of yet.
 

someotherguy

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Black wire all by itself with a ring terminal, screwed to the metal tab that the ALDL connector is on, most years of the TBI trucks that's the arrangement. That's the gauge cluster ground.

Mind you, over the years other people may have grounded aftermarket stuff to that same tab because it's in the area.

Richard
 

Lgarretto

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Yeah. The tab is there. Nothing is connected to it. The wire was cut at some point and moved
 
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