Why do my gauges peg out?

[rdrunning]

hey guys, i am trying to get the gauges to work on a 1973 satellite and as soon as the key is turned on they peg out. if i disconnect the wire from the sensor it goes back to "zero"

the gas gauge does it, temp and oil pressure.

any thoughts?

 

[Hemi Rebel]

Check the ground strap on the engine. Voltage may be backfeeding and finding an alternate path to ground though the guages

 

[rdrunning]

Check the ground strap on the engine. Voltage may be backfeeding and finding an alternate path to ground though the guages

I have aver added two large ground straps that go from the motor to the chassis. So it's definitely got a good ground going on, good idea though

 

[440+6]

Could be a bad dash voltage limiter that is stuck on and giving full power, don't let them peg for long they will fry.

 

[rdrunning]

Also the lights in the dash have never worked, I replaced the headlight switch hoping that would fix the problem but no go. Does the cluster ground to the chassis somewhere ?

 

[440+6]

The cluster screws do the grounding, but I always add a ground from the cluster to the steering column on mopars.

 

[Meep-Meep]

Likely the voltage limiter isn't limiting and the gauges are seeing 12V. They should only see about 5V.

 

[hunt2elk]

Likely the voltage limiter isn't limiting and the gauges are seeing 12V. They should only see about 5V.

I agree. Don't leave the key on to long, because the gauges wont last long with a full 12v going to them.

 

[rdrunning]

thanks for the ideas guys and the heads up about not letting them peg out.

I took a voltmeter and measured the voltage at the sensor (where the wire connects to the sensor) and i am getting a pulsing 5v. Pulsing= around 5v for a second then it drops to about 1v for a second, and continues back and forth from 5v to 1 v. this is going on with the key on of course.

 

[Jim Bob The Dancing Bear]

They are 45 bucks at napa. It may be worth the cash just to insure that isn't the problem and you know the gauges are protected.

Rebuilding the gauges are expensive in comparison. Cheap insurance.

 

[Meep-Meep]

You can also buy a solid state regulator upgrade kit. I have made my own out of a 7805 voltage regulator, but as I understand those can at times send a full 12V to the gauges momentarily. One of the conversions I did was on my old 71 Ranchero and if the car sat for a while the gauges would peg for a bit then settle down. This might be due to large voltage swings in the charging system and if the input voltage is too high those solid state regulators can't properly regulate so they just freak out. On my old 68 Mustang I never has such issues but the car was driven every day, so system voltage was more stable I suppose.

 

[rdrunning]

is the voltage supposed to go all the way through the sensors? or is it supposed to be contained to just inside the sensor

i am getting voltage all over the outside of the water and oil sensor, and as soon as i touch them to the block it pegs out.

i was always under the impression that the insides of those things were insulated

 

[hunt2elk]

You do have a ground from the battery to block and block to firewall? The instrument cluster is grounded through the dash frame, but you could run a jumper there to be sure.

 

[rdrunning]

Success!

So i had an old temp sensor laying around and i swapped it and it didn't immediately peg out. I let the car warm up and for the first time i have a working temp gauge.

The sensors are supposed to contain the 5v that are supplied to them. Simply put, you should not be able to measure voltage ANYWHERE on the sensor but the very top where it plugs in.

Best i can figure is the insulation fails and your 5v gets grounded into the block causing the gauges to freakout.

thanks for all the input!

 

[440+6]

Good deal, I'l remember that one.