I have a 78 GMC 6500 dump truck. It has a ton of electrical issues so I'm basically starting from scratch. I've wired in a new key switch and have good power from my battery going to my starter, distributor, and acc. I am however not getting power under the hood to my fuel pump. I pulled a new wire for the fuel pump and when I give it 12v with my power probe it kicks on. It is not getting power though when I turn my key switch to on. This is one of the trucks with 2, 11-pin relay blocks under the hood on the drivers side. I have a good 12v coming into the relay block and 12v going through my relay to my ignition. But when I probe my fuel sender wire I get a ground. Any ideas on how to get power to go through the relay block to my fuel sender?
Fuel gauge gets 12v in dash. Fuel sender is variable ground to fuel gauge.
If that has the old 2 piece bulkhead wire terminal blocks going through the firewall held together with a 3/8hex bolt in the centre, they are known to give problems and have to be separated to check the actual wire terminals for heat damage and continuity. Sometimes one or more are distorted and the surrounding plastic is partly melted. From the factory there is a black sticky stuff gooped inside to keep out moisture and prevent corrosion
Thats exactly the setup I'm looking at. I've got a ground through my fuel sender (terminal 8) so is it an issue of needing to get 12v through the fuel gauge? My whole dash is basically pulled out and its a rats nest of wires.
“ But when I probe my fuel sender wire I get a ground. Any ideas on how to get power to go through the relay block to my fuel sender?” You saw a ground because its sorta supposed to be a ground. The sender is a ground for your fuel gauge. Your power probe thingy detected enough of a voltage drop to make it look like a ground. Especially, if the fuel level is low. People don’t think electrons be like they do, but they are.
You need to check for 12v at the fuel sender terminal with a voltmeter. Digital is the most accurate. Analog voltmeters are a thing of the past and not as accurate. A fuel sender is a form of a variable ground and the gauge basically converts the small current flow to needle movement in the gauge. So usually if you ground the wire at the sender, the gauge should read full. Most fuel gauge malfunctions( if 12v is present) are caused by a bad ground at the sender or a worn out sender