88build

I need to find out what wires operate the fuel gauge. I installed a non stock sending unit but I want to keep the use of the original fuel gauge in the dash. I thought I had it but when I turn the key the needle goes right to full with a bone dry tank.

87notch408

I am trying to figure this out as well. I am putting a fuel cell in my project and most come with a 0 - 90 ohm sender which is typically GM (from what I have figure out)
I also believe that the Fords use a 33 - 240 ohm sender???????
Like I said, I am trying to figure this out because I found a great deal on a 10 gallon sumped fuel cell that fits right in the spare tire hole on my nothch. I want to maintain my stock gauge.
Do you know what ohms the sender you installed works in?

88build

The sender is to a 67 mustang. I put a 67 tank in my 88 so I could have that nice looking cap between my tailights. I know ford changed alot from year to year but the sender is still a rheostat at heart. I do not know what ohms either one is. I can't believe I'm the first or only one to do this.

evintho

The reason your gauge goes to full on an empty tank is because................
A) The resistance on your '67 sending unit is different than the calibration on your '88 gauge, or...........
B) You have a bad ground.

First find out what the resistance is on your '67 unit. The calibration on your '88 gauge reads 33 ohms as empty and 140 ohm as full.
Next, run a seperate ground wire from just behind the connector that comes off your tank to a dedicated, good ground. That will confirm a good ground.
The problem is probably A.

88build

I just read your reply but have not gone out and looked. Where for the ground? Is it a seperate wire connected to the sender or can I just ground the tank. I'm going to go look now. What do you mean behind the connector?

88build

I found online that a 88 fuel sender is 16-158 ohms. Doesn't seem that far off, or is it?

evintho

Climb under the back of the car. About in the middle of the tank, tucked up between the tank and bumper should be a fairly long, round 4-prong connector. Disconnect it. The YEL/WHT wire is actually the sending unit wire. The black wire is the ground wire. I don't remember what the other 2 wires are for but it's not important now. Attach a small aligator clip to the end of a 16 ga wire. Clip the aligator clip to the prong, inside the connector that's attached to the black wire. Run the other end of your wire to a good ground. If the needle still goes to full with an empty tank you've eliminated one of the culprits. Your factory ground wire is good. As stated, it's probably a different resistance in your sending unit.

My 33/140 is straight out of the factory shop manual for my '89. Maybe there's a slight difference between '88-'89. Doesn't make any difference though. I just had my Autometer Phantom fuel gauge recalibrated for my Mustang by Autometer. Their gauge read the high number as empty and the low number as full. They reversed the resistance reading and recalibrated it for 16-158 ohms. It's a slightly wider range so maybe the needle will bottom out when there's still a bit of fuel left in the tank and it may top out when it's not completely full. Either way, it should work.