Need advice from the pros!!!

[christineman]

I have a 69 rr. The temp and hurl gauges don't work. I've tested both with hot wire thru the reducer and when I ground the other post they both go up. Problem is in the car, when put juice to either of the gauge posts, it's a dead short. What's the problem? Both posts should not be gounded. Advice please??

 

[Beekeeper]

Does the fuel gauge work? To test the gauges while in the circuit you can ground the sending unit wire
to the chassis at the sending units one at a time.
If you get deflection on the gauges the sending unit
is faulty. Both post on the gauges are referenced to ground. Between the posts inside the gauges is a coil of resistance wire wrapped around a nichrome strip
that bends when heated by the resistance wire. So from the 5 volt reference voltage through the gauge and out to the sending unit to ground. The amount of resistance to ground is controlled by the sending unit.

 

[PurpleBeeper]

maybe a problem with the circuit board the gages are plugged into?

 

[christineman]

Does the fuel gauge work? To test the gauges while in the circuit you can ground the sending unit wire
to the chassis at the sending units one at a time.
If you get deflection on the gauges the sending unit
is faulty. Both post on the gauges are referenced to ground. Between the posts inside the gauges is a coil of resistance wire wrapped around a nichrome strip
that bends when heated by the resistance wire. So from the 5 volt reference voltage through the gauge and out to the sending unit to ground. The amount of resistance to ground is controlled by the sending unit.

So both sides of the gauges are full grounds??? If that's the case how does the regulator get juice to the gauge? When I t
Put the regulator in, I get sparks. That's not a good thing on a gauge. It finially blows the reg

 

[Beekeeper]

So both sides of the gauges are full grounds??? If that's the case how does the regulator get juice to the gauge? When I t
Put the regulator in, I get sparks. That's not a good thing on a gauge. It finially blows the reg

No both sides of the gauge are not full ground the sending units provide a resistance to ground. The lower the resistance the more current through the gauge element and vice versa.

maybe a problem with the circuit board the gages are plugged into?

This could be a possibility there is a full ground circuit on the board for the instrument lights.

Unplug the instrument board connector and the sending wires at the oil and temp sending units
and check them to ground to be sure they don't have continuity to ground. Also again does the fuel gauge work?

 

[christineman]

No both sides of the gauge are not full ground the sending units provide a resistance to ground. The lower the resistance the more current through the gauge element and vice versa.

So then, with circuit board, gauges and limiter replaced, what could b the reason both gauge terminals be grounds?? Would that little condenser be the problem?


This could be a possibility there is a full ground circuit on the board for the instrument lights.

Unplug the instrument board connector and the sending wires at the oil and temp sending units
and check them to ground to be sure they don't have continuity to ground. Also again does the fuel gauge work?

 

[Beekeeper]

It could be the noise suppressor/condenser you could just unplug it from the board it's only purpose
it to suppress the noise created by the voltage limiter cycling to regulate the voltage from 12 to 5 volts so you don't hear it in the radio.

Give me a little more info about the car. Where the gauges working before? did they quit suddenly? You say it blows the regulator? Have you installed a new one?

This is a very simple circuit it starts with 12 volts to the limiter then out of the limiter is 5 volts for gauge reference this goes through the gauge and all the way to the sending unit. If you unhook the wire from one of the sending units and ground it to the chassis the gauge will go to full and if left for more than a few seconds it will fry the gauge. The sending units provide a resistance to ground to prevent the circuit from being a dead short. Now if one of them is shorted out to ground this could be your issue.
Try unhooking the sending unit wire from the fuel,oil
and temp sending units and make sure they are clear maybe tape the ends so they don't come in contact with any parts of the chassis. Then install the limiter and see if all is well.

 

[christineman]

I have both fuel and temp senders unhooked but, If I apply 12v to the ignition post on the limiter (which should be normal, then apply 12v to either side of the gauge,
The reason I applied 12v to the ign post on the limiter is because with the key on, there is no voltage to the ign post on the limiter.

 

[Beekeeper]

Ok you should never apply 12 volts directly to the gauges this will indeed destroy them. The most they ever see is 5 to 7 volts. There are three posts on the limiter one is obviously the ground the center post is 12 volt input from ignition and the other is the 5 volt
source for the gauges. Unplug the limiter and turn the ignition to run and check for voltage at the center limiter socket. Have you did this already? Let me know what you find or found.

 

[Beekeeper]

So did you find the problem?