for the instrument cluster on my '71 Cutlass SX. The gas gauge pegs to one end when the ignition is turned on and I heard it might be the voltage regulator. Does anyone know where is it, how can I test it Thanks!

 

It is most likely a faulty sending unit or bad wire shorted to ground in the system. I don't think the Voltage regulator would be associated with this problem even if it was bad. Not sure about the '71 Cutlass but I think the voltage regulator was on the firewall just inboard of the windshield wiper motor/pump assembly.

 

The voltage regulator is on the firewall right above the engine. It is black box about 2-2.5 inches in diameter. I really doubt that is your problem. It sounds more like a short or open wire coming from the sending unit or maybe a bad sending unit.

 

Voltage regulator and fuel gauge are not related, in any way.

Norm

 

While I agree that the problem is almost certainly not related to the voltage regulator, this statement is not entirely correct. The voltage regulator obviously powers the voltage divider circuit that operates the fuel gauge. On the other hand, this circuit is somewhat self-compensating such that variations in input voltage do not affect the gauge reading. The more important point is that problems with the voltage regulator would show up as much more obvious electrical problems, such as dim or overly bright headlights, undercharged battery, etc.

The problem is more likely in the gauge circuit itself, either a bad sender, a broken wire from the sender to the tank, a bad ground on the sender, or a bad ground in the instrument panel.

 

Thanks for everyone's suggestions. I'll start with the sending unit and work toward the instrument cluster. (an old gas station mechanic suggested the regulator idea to me)

 

an open circuit in the fuel gage system is the primary cause of a pegged(to the high side) fuel gage. could be the tank ground or wiring to the front from the tank. first, i would check the connector in the trunk, then the tank ground and tank connectors. you can check the gage and wiring to the gage by connecting the gage wire(at the connector in the trunk) by grounding it momentarily. it should drop to empty during grounding.


bill

 

Lower your tank (if you have to) pull the positive potential (not the ground) wire off the connector on your sending unit, (careful not to pull the wire out of the rubber socket) then turn on your ignition, touch the wire to ground, if your gauge moves to empty, then your sending unit is bad, if it stays on full or pegged, you have a broken wire as suggested by others....gl

 

you can do this at the connector in the trunk.


bill

 

This might seem too obvious, but your gauge will peg out if the wire becomes disconnected from the fuse block. This happened on my Chevy truck. Drove me nuts till I got down there and discovered what happened. However a 37 year old regulator might be worth replacing anyway, just to eliminate any present or future problems. Did that on both my vintage vehicles and solved a bunch of problems. Chumley

 

That gas station mechanic may have been a Ford man. My Cougar has a separate voltage regulator for the dash wiring.

 

I had one of those go bad on a 77 Thunderbird, and the gages did all sorts of scary things. Kinda unnerving to watch temp peg hot, oil drop to zero, and fuel wave all over. The telltale sign was the voltmeter was doing the hucklebuck too.

 

Yep, lots of Fords have the separate little regulator for the gauges; my 78 Ford does. The 71 Olds gauges do not use a separate reg.
The fixes were all mentioned above.