Fuel gauge woes

[bblawless]

Hey guys. Been chasing down issues with my fuel gauge in my 79 BJ40. A while back I was out wheeling and out of nowhere my fuel gauge started reading over full, and was just stuck there every time the truck was turned on. I pulled the sender and tested it- it seemed good, and I tried throwing a spare in there too to no avail. Checked everything on the back of the cluster (new) and it seemed good, even swapped in my original fuel gauge to rule that out with no luck. Now ive had a bunch of stuff apart over the last couple weeks so it’s a little hard for me to keep track of what I’ve messed with here but this is where I’m at now. I’m getting no power at the harness (at the sender) and the other weird thing I only noticed today is that the dropping resistor on the back of my cluster is piping hot when the truck is on. Like too hot to even touch, I literally burnt my finger grabbing it this morning. I pulled the resistor too, tested it and even swapped the resistor to make sure it wasn’t the issue…

So I’ve got no power at the tank, a piping hot resistor, no reading at all on the fuel gauge now and I’m confused and frustrated lol

Hoping someone on here can chime in and tell me what I’m missing.

Cheers guys

Benny

 

[charliemeyer007]

I don't know for sure but the ammeter drops the voltage to the fuel gauge on a 12 v gas engine system via a resistor.

You might have a resistor that was for a 12v system - put 24 volts on it could cause it to run hot. No power at the sender - bad fuse, check it with a meter - they can look good but actually be bad. Wiring has a break, corrosion crawling under insulation from the crimp on the connector - continuity check on the wire.

Coolerman's wiring diagram and parts

Cruiser Wiring

 

[anothernz45]

Is your BJ 24volts? I'm wondering if the 5 volt regulator built into your fuel gauge developed an internal short while you were bouncing around - there are little wires just looped around inside there.
Try unhooking the fuel sensor wire at the gauge and check it for an earth fault - may have rubbed thru somewhere

 

[TreadingLight]

There shouldn't really be "power" at the sender. The gauge measures resistance and there is little current involved.

I think you may have a wiring issue between the sender and gauge. You can confirm this by checking for continuity between the wire at the sender and the wire going into the back of the gauge. I believe it is yellow/black.

Also make sure you have a good ground wire going to the sender. That would be a white/black wire.

If b/w doesn't have continuity to ground, or y/b doesn't have continuity from sender to gauge, then you can trace and fix the wire.

 

[TreadingLight]

Try unhooking the fuel sensor wire at the gauge and check it for an earth fault - may have rubbed thru somewhere

I just noticed where you said the gauge is pegged high. I agree with @anothernz45, sounds like the y/b wire is shorted to ground. The gauge goes on full when that happens (and the gauge itself may be damaged by it).

 

[JVZii]

I think @TreadingLight may be right. If the fuel gauge goes right to Full and stays there, there was likely a short in the line going to the sender/the sender shorted out. This would also explain a hot resistor as you are putting a lot of energy through the cluster. I am curious if you have a reading on the temp gauge, it is powered by the fuel gauge.

I have a video on how to test the gauges themselves. This may help a little...but if there is a short between the cluster and sender this may be your problem