Hey guys,

Just got my new tank, sending unit and pump installed in my 84 T/A. The sending unit and pump are for an 89, just using them regulated down so I have a reliable fuel pump. My problem started when I pluged the new harness on the sending unit into my factory vehicle harness. The new one and my factory one are keyed the same. The gauge read way past full all the time even though the tank was empty. Put 3 gallons of gas on the tank and still full all the way (figured tank was totally empty so it needed more in it to get a "reading" to actually read right). Another problem was the Pump wouldn't come on. No power to it. So, two problems. First, I tested for power on the car harness. On one lead I was getting 7.5 volts. Thta was the middle "pink or purple wire". On the orange wire where I should get 12v for my pusher pump, I got nothing. I then tested 12V on each lead to find which wire turned the pump on. Found it, now the pump runs fine. Using the factory harness, ti's the orange wire. Or should be. I even checked for a fuse in the fuse block..no fuse. Put a fuse in, still no 12 volts.

I ran a power wire to the back using an existing relay I put in a few years ago and tested the leads to see which turned on the pump. It is the orange wire. So I spliced in on the car side so I could use the factory connector.

Mabe the new harness and my car harness are wired differently, so I'm going to play with the wires to see if I can get a reading to change on the fuel gauge. Does anyone have any suggestions as to why it would be reading max full?

Figured it would be plug and play. Not so much luck. Possible I burned something out testing the 12v on the other leads?

Any help would be appreciated. Thanks!

 

I don't know about the '84 - although I think it should be the same, but my 88 doesn't have a fuel pump fuse in the fuse block, its connected thru a wht/tan wire at the relay thru an org wire to a 20amp inline fuse at the battery.
I replaced my pump/sending unit in 2006 with a used '85 and it was plug & play.

If the tank is empty then the float is stuck in the full position, or there's no connection to the gauge.
Disconnect and ground the wire going to the gauge(on mine it's pink,) it should read empty if not you may have a gauge problem.

Don't leave us hanging - post your results.

 

The gauge worked...mostly (ran empty when it read 1/4 tank on me) before I pulled the tank/sender. Plugged in the new sender is when my problems started. Do you know which wires are supposed to be which on the vehicle harness?

 

At the connector attached to the body just above the rear axle there should be:

1. Tan/Wht to fuel pump
2. Pink to sender
3. Blk pump/sender ground

You can see the wire colors at the sending unit flange in the picture I attached to my reply #5 at this post https://www.thirdgen.org/forums/tech...-question.html

 

I'd check the ground wires and make sure none are broke or missing.. Mainly the one from the battery to the body. I had a couple issues like yours when I changed my sending unit, gauge read wrong and the 7.5 volt thing sounds really familiar too. I had forgot to connect the ground to the body, as soon as I did everything worked.