Dash gages not working

[Paunlimited]

68 gtx doesn’t have fuel ,temp gages tac and radio working. All lights work even radio light glove box console courtesy. Any good ideas or is it possible they are all bad. Car has sat since 74

 

[Beekeeper]

If the fuel,temp and oil gauges don’t work the first thing to check would be the fuse. Next would be the voltage limiter for the gauges by making shure it has 12 volts going to it.

 

[furyus]

If the fuel,temp and oil gauges don’t work the first thing to check would be the fuse. Next would be the voltage limiter for the gauges by making shure it has 12 volts going to it.

I agree with this. The voltage limiter can be bad. I have found that the gauges in late 60's Mopars are not the best quality. Went through 3 temp gauges on my Dart to find one good one.

 

[Paunlimited]

How can I check the voltage limiter and what plug location is the capacitor? Plugged into the 5 volt 12 volt ?

 

[Beekeeper]

The limiter is on the back of the instrument cluster circuit board just plugs in. It needs 12 volts into it if it has 12 volts coming to it with the ignition in run I would try a known good one in its place.

 

[Paunlimited]

I have the limiter out and was trying to test it. As I pulled it out the capacitor condenser (whatever it is ) pulled out also but I couldn’t see where it came from. Any ideas on both how to bench test and location for the plug

 

[Jerry Hall]

How can I check the voltage limiter and what plug location is the capacitor? Plugged into the 5 volt 12 volt ?

The plug in limiter on the back of the cluster is what changes 12V to 5V. Look at the service manual. You should have 12V in, ground, and 5V out on the limiter. There is a solid state transistor conversion kit available that makes the 5V much more stable.

 

[Beekeeper]

The condenser is just for suppression to eliminate
radio noise. As Jerry stated RTE makes a nice limiter and it has an led on it for
trouble shooting.

 

[Nacho-RT74]

depending on the fail you can get burnt oil, temp and gas gauges with a limiter failure. I.E. if lost the ground in whatever way, internally on limiter or cluster ground, the points on bimetallic keeps closed allowing to pass all the full 12 volts. This will burn the gauges in less than a second.

Radio failure has nothing to do with cluster fail. That could be very well a fuse. usually shares the fuse with turning lights. Do you have turning lights ?

you can test a voltage limiter feeding 12 volts and ground and checking for a pulsating signal coming out from limiter output with a test light or analog multitester. Of course you can't check if the pulses gives correctly the 5 volts RMS ( needs an osciloscope for that ) but will know if is in working order.

Tach gets its source from accesories network... maybe linked with Radio and Turnings ?

SOME CARS gets the cluster feeded out from ACC circuit and some others ( 71/74 B bodies WITH standard cluster ) gets it from RUN ( Ign1 ) circuit. Can't tell your case, would need to check the diagram.

 

[Paunlimited]

Cluster problem was a cracked circuit board so new one ordered and will see if that’s the issue or are gages burnt also. Fuses all good so maybe bad radio. Tac who knows. Must be bad also as it has 12 volts and a good ground. Turn signals work fine. Limiter checked good but ordered a new one. Seems odd that many electrical problems except the fuse block had foil from cigarette packs on every fuse. Replaced all harnesses and fuse block so wasn’t expecting these problems