. Spring problems

[Northern Pony]

Stumped!
I did a fix last fall that did not fix every thing. The problem I had was while driving I lost gas guage, oil pressure and temperature. All of these guages still showed something but were low. Last fall I changed the small voltage regulator at the back of the instrument cluster. Now the gas guage and oil pressure read correctly, but temperature is like it is recording nothing. This is while the car is running. If I shut off the car and turn the ignition to accessories, I get a temperature reading. Turn the ignition all the way on to running and the temp guage goes back to no read. Of course there has been a delay here as the car has been in it's winter storage for the past five months. That just explains why I did not search an answer sooner, and has nothing to do with the problem.
Any thoughts? I know that someone on this site has the answere, and I appreciate any help I can get.
BoB

 

[CougarCJ]

Check your engine to firewall ground strap.

 

[J.Bart]

what about the ignition switch?

 

[spoiler]

Bob that does sound like a ignition switch problem,if the temp gauge works on" acc "and not the "on "position. Maybe it has just been a unusually cool spring(up here) and your C/S is trying to tell you to head south. Good luck ! Reg

 

[CJ]

Oil-Pressure Gauge
Like the fuel and coolant-temperature gauges, the oil-pressure gauge reads based on the amount of power flowing across it to ground. The oil-pressure sending unit has a spring-loaded piston inside. The piston moves a contact back and forth across a variable resistor. Power flows through the contact across the resistor to ground where the sender is screwed into the oil galley passage. When there’s no oil pressure, there is high resistance across the sender, which leaves the needle at the far left side of the gauge. Fire the engine and put oil pressure to the sender and watch what happens. The contact moves across the resistor to a lesser resistance value, which increases the flow of electricity to ground from the gauge. The needle moves toward maximum.
When an oil-pressure gauge isn’t working, most of the time it’s a faulty sending unit or severed lead to the sender. When in doubt, ground the lead and watch the gauge. It should peg the needle.

Mustang Monthly

 

[franklinair]

Does the gas gage function when in the ACC position?

Neil

 

[Northern Pony]

Neil;
Yes the gas guage operates normally in the ACC position.

CougarCJ
The ground strap is good.

It may be the ignition, but the original problem was with the voltage regulator and I'm still thinking there may be something there.
BoB

 

[franklinair]

I'll have to review my wiring diagram:
Power (12V) is sent to the VR from the ignition switch thru the RUN or ACC contacts on the ignition switch. The VR doesn't differentiate the 12V source (RUN or ACC). The VR then steps the voltage down, powering the gages at a lower voltage. The gages are seeking a ground through varying resistance (ohms) to deflect the gage pointers. From what you say, the Fuel gage works with the ignition switch in either RUN or ACC which tells me the ignition switch should be OK (powering the VR in both positions).
I'll check my diagrams tomorrow.

Neil