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Discussion Starter · #1 ·
I'm still trying to check the ground on my fuel pump wiring. I have the square, four-wire electrical connector unplugged from the top of the fuel pump assembly (tank is still in place). I've tried to pull back the harness plastic tubing but the wires are still coated with some dark gray covering. I cannot tell which wire is which.

The square connector has two contacts across the top and two across the bottom. I'd like to see a diagram of which is the gray 12V for the fuel pump, which is the fuel pump ground, which are for the sending unit.

I found this wiring diagram for a 2001 Jimmy, and it's helpful, but it doesn't help with figuring out the connector. The wires are F1 gray 12V for fuel pump, Black 1650 utility.

 

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Discussion Starter · #2 ·
Some progress... my 12 year old son was able to get his arms up to the connector so we could test the contacts. Here is what we got:


1998 Jimmy 4WD 4-door
Looking at the square plug, large clip to left

TOP LEFT CONTACT
4.6V steady with key "Run"
Assume this is power to sending unit

TOP RIGHT CONTACT
10.6V for 2-3 seconds when key switched to "Run"
Assume this is power to fuel pump

BOTH BOTTOM CONTACTS
Ground


We first checked each one independently with the voltmeter gauge grounded to the frame. Then we checked the TOP RIGHT grounded to each of the BOTTOM contacts and got the same voltage. So I believe this confirms my ground wires are good.

I don't know why I'm seeing 10.6V instead of 12V+. I should've checked the battery voltage but it was raining. The battery had run down and was on the charger for a few days.

If I could find the same male plug (anyone got an electrical plug number?) I would wire it to a full 12V and plug it into the pump.

I looked high and low under the hood and still cannot find the fuel pump test connector, supposedly coming off the harness near the ABS or by the center firewall. Some 2nd generation Jimmy's supposedly never got one; maybe this is one of those.

Anyway, I think my pump is bad. I've gone through all this because dropping the tank has become a nightmare. The front strap bolt and nut are solid rust. After a week of spraying with PB Blaster I finally got the nut to turn, but the strap is getting all twisted and bent. I'd like to cut the threaded rod a lot shorter to lose a bunch of the rusted portion, but I'm not crazy about showering the tank with sparks from a grinder. Maybe a Dremel and be careful with spark aim?
 

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i saw what you did there!
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voltage drop in the FP wire

it happens and if its too much then the pump cant pump enough pressure or volume and will cause hard starts or no starts

ive had to repair this around 8 or 10 times on various trucks over the years by runing a new wire to replace the original

and purple wire is fuel level sender wire
 

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Discussion Starter · #4 ·
Oooooooooooooooh...............

Ok then, I need to check the voltage at the battery. Then I should probably try to put a real 12V to the fuel pump to see if it runs.

Could low voltage cause the pump to not run at all? I don't think it's running at all. I suppose the combination of low voltage, fuel filter getting dirty and age could kill the pump. So another thing I may have to fix....

Thanks for the quick reply!
 
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