1970 Dash gauges not working

[Richard H.]

Hi Guys,

Thanks for the continued help with this project!

I have a 1970 coupe and at this point three gauges do not work. The temp gauge, gas gauge and the charging gauge do not work.


This is what I know at this point:

the fuse is good and there is 12 volt power to all the gauges with the ignition switch on.
the dash is grounded at the temp gauge, I added another ground wire to make sure.
I do not get an omhs reading at either gauge.
I would like to bench test all the gauges before I proceed.
My question:
can I bench test the gauges? I believe the gas gauge can be tested by putting 12v power to the gauge and a ground wire to the ohms side I should get an empty reading. If I run a ground wire to the gound post on the gauge it should peg the gauge? Is this correct and if so can I bench test the water temp gauge and the battery gauge the same way?

Thanks for the help
Rich Harris

[William C.]

Re: 1970 Dash gauges not working

Temp gauge is a direct read based on resistance thru the sender, so it can be checked directly. I would be very careful with the ammeter, if it is the same as a mid-year configuration (amps, not volts) it is actually reading the voltage drop across the ends of a feed wire in the harness and inferring current flow from that reading. any attempt to 12V "test" it will IMMEDIATELY fry the gauge, at least in a midyear, so check your wiring diagram to see what it actually measures. The service manual I believe has a test for the fuel gauge.

[Terry M.]

Re: 1970 Dash gauges not working

Temp gauge is a direct read based on resistance thru the sender, so it can be checked directly. I would be very careful with the ammeter, if it is the same as a mid-year configuration (amps, not volts) it is actually reading the voltage drop across the ends of a feed wire in the harness and inferring current flow from that reading. any attempt to 12V "test" it will IMMEDIATELY fry the gauge, at least in a midyear, so check your wiring diagram to see what it actually measures. The service manual I believe has a test for the fuel gauge.

Bill is absolutely right about the amp gauge. Pay attention to what he says or you will be buying a new gauge. I think the resistance for the fuel gauge sending unit is 29 ohms when the tank is full, but don't trust me. I have too many cars of different generations in my fleet and could easily be mixing them up. Follow the directions in the 1969 or 1970 Chassis Service Manual.

[Alan S.]

Re: 1970 Dash gauges not working

Hi Richard.
Here's a link to some detailed gas gauge information from John Hinckley. As John indicates it can be used for 68+ cars too by changing the ohm value.
Perhaps it will be helpful to you.
Good Luck.
Regards,
Alan

https://www.forums.ncrs.org/showthread.php?81801-C-3-fuel-gauge-trouble&highlight=gauge