Fuel sender electrical troubleshooting inside!

scoob8000 · Oct 2, 2008

Can anyone tell me what the 4 wires are at the top of the fuel tank?

I'm troubleshooting my gauge not working.

Key on, gauge shows empty
All other gauges work fine
short yellow/wht to the black lead, gauge reads full
tank is full, reading between the pins for the black and yellow/wht reads 140ish ohms
Ohm reading bounces slightly as I bounce the truck around
I also replaced the plastic 4 pin connector which was badly corroded.

What are the rest of the wires, is there more than one ground and I'm using the wrong one?

scoob8000 · Oct 2, 2008

Update:

Found a schematic in my haynes book.

Looks like:
yellow/white = sender
black = ground
black = ground
pink/black = pump +

But I only have one black, and I have a heavy orange which isn't in any schematic. <scratches head>

Earl43P · Oct 2, 2008

The sender is actually grounded to the metal of the in-tank unit, "case ground", which is tied to BK. So, black and black on the tank side should be continuity (~0 ohms).

PK/BK is FP +
BK is FP ground
BK/Y is sender ground
Y/W is sender

This is for a 93.

Update your profile / sig. and we won't need to guess what year you are asking about.

145 ohms = Full
22.5 ohms = Empty

You can turn the key off, short Y/W to ground and watch it go to E when you turn the key back on. It may have an anti-slosh circuit, so turning the key on/off is "key".

FWIW, you may simply have the classic "perforated brass float filled with gas" problem. $8 @ the dealer for a new brass float. The sender assembly is also take-apart-able. You may break the plastic clips and ruin it though, they get brittle. They lose spring tension on the wiper or the wiper point wears out = new sender.

scoob8000 · Oct 2, 2008

Profile updated.

I'm seeing 142 ohms with a nearly (about 20 miles off a full tank), so sounds about right there.

One of my wires is definitely orange though.

FWIW, it's the heaviest wire of the four too.

[edit]

Just found this pic. I know its not the right pump, but the wires are very apparent as to which pin is what.

Black is definitely my tank ground, and my mystery orange is the pump ground.

I checked, I have good continuity between both ground wires and ground. The pump primes with key on, so that one is good.

I'm gonna stop at rad shack and get some resistors tommorow to test the gauge with. Grounding yel/wh shows full..

[edit]
Update again. I picked up a new pump and sender just for comparison. The new unit reads 20 ohms full, 80 ohms empty. I'm guessing the sender on my stock unit is all corroded up. Gonna pull it tomorrow to see.

scoob8000 · Oct 7, 2008

I just wanted to post an update to this for any one in the future that might search for this....

Finally fixed my problem. I had two. My float was full of fuel and had sank, AND the sending unit coil was all gunked up.

I was in a hurry to get things back together so I just bought a whole new unit from IdontknowZone kept the original to repair..

Fuel sender electrical troubleshooting inside!

scoob8000

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Earl43P

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