1980, 720 instrument cluster

[The Newt]

I have a 1980 Datsun 720. Previous owner pulled the dash and cut the main harness because marker lights were not working. I have probably 1,000 problems I’m currently working but I’m going one at a time. My fuel gauge isn’t working and I see there is nothing to plug in to the back of the instrument cluster besides two plugs and the Speedo cable. It appears like there may have been two plugs for the fuel gauge and coolant gauge? Any help on that would be greatly appreciated and then I can list the other 999 problems I’m working on 🤦‍♂️

[datzenmike]

Both gauges are on the 12 pin connector to the gauge cluster. Coolant temp is the the Yellow/Black stripe wire and the fuel gauge is the Yellow/White stripe.  NOTE that if the temperature gauge is also not working the problem may be the common voltage regulator that powers both gauges.

 

 

If you look under the front of the passenger seat you'll find a 10 pin connector to a harness that goes through the floor. Again the Yellow/White stripe wire goes to the fuel tank sender. If you unplug and ground the Yellow/White wire with the ignition ON you should observe the fuel gauge go to FULL.

 

If it does then the gauge is functioning properly and the problem is either the wire to the sender in the tank, the sender in the tank or the tank is not grounded. The most likely is the sender wire or the ground wire has corroded and fallen off the tank.

 

If it fails to read then the problem is towards the gauge possibly the gauge.

[The Newt]

Great information, thanks! I will check it out soon hopefully. When I got this pickup ($100 and a clean title) I knew I would have a fair amount of work to do. The previous owner cut the main harness at the firewall and disconnected it from the motor after pulling the dash out. I think I have a majority of things hooked back up but now I’m trying to get small things working like brake lights, marker lights, turn signals etc. I also need to to figure out why the hydraulics for the dump bed are not working. So far I’ve had to connect the main harness back together, slave cylinder and a battery out of the Benz. It’s running great now and I’m excited to finish it up and use it before the snow hits.