i have a 1966 ford mustang fuel tank with the ford fuel sending unit.
i bought aftermarket tpi gauges. fuel gauge shows half tank when the fuel tank is empty. the sending unit that came with the gauges wont fit the tank.
what do i do. thanks shawn

 

Shawn -

First, you'll have to get a Ford sender that fits the tank. Then, you can calibrate the sender to the gage.

The gage in my 56 was doing something similar. I realized that the sender and gage must have been in the ball park with each other and that I could either put a resistor in the sender line to dial it in (George helped me scope that out) or I could recalibrate the sender to match the gage. I did the latter.

I took the sender out of the tank and reconnected the sender-to-gage wire using a jumper. I also used a jumper to ground the sender to the chassis. I laid the sender on a piece of cardboard marked for the tank height (I stuck a tape measure down thru the sender hole to find an accurate dim for the height). I put the sender mounting face on the line for the tank top and started working the float arm up and down. The gage responded. I adjusted the float arm length and the up/down position of the float pivot clamp until full up and full down on the float arm read full and empty on the gage. Reinstalled the sender. All has been perfect ever since. The whole operation took about an hour.

If that excercise doesn't fix the problem, you may have to add a resistor to the circuit to get the gage and sender resistances to match. But do the above excercise first. It is the easiest to do.

 

There is a pending tech article that has the following information (courtesy R. Ferguson) in it. As Randy said, you have to find out the resistance range of your new gage and get a sender that matches.

 

Would a small rheostat work to dial in that reading? I've put in a 65 mustang tank and sender with stock 51 gauges. I'm showing half a tank when I only put in 4 gallons (16 gallon tank). I was looking in the drawer of resistors at radio shack trying to figure out what to do and they had a small selection of rheostats that got me thinking. I'm no electrician so I ask would something like that work?

Scott

 

i own a 66 mustang, remember the 66 fuel gauge is 6 volt. the guage you bought may be 12 volt. there is a voltage reducer on 66 guage's to make them capatable with 12 volt system. the sending unit on a 66 tank is set up for 6 volt.

 

A rheostat is a adjustable resister - so yes you can use it. As an electronic tech I often used rheostats to find the best resistance value, and then changed them out for a resistor of that value. You just wire one lead to the wiper, the other to either end. When you adjust it the value of the resistance changes.

In fact, your sending unit is exactly the same thing - a wire wound rheostat with the float moving the wiper.

I am not sure that adding resistance to the circuit will work and fix your problem, but there is no difference in adding a resistor or a rheostat.

 

i reread your post a few time's, when i went with a 12 volt conversion on my 49 before i tore it apart. i put 12 volts to the stock guage and 30 om's at the sending unit on tank. i drove it for a year like that and had no trouble with it.it read correct too. hope that help's.

 

I may try the rheostat to at least get my "low fuel" side of the gauge somewhat accurate. I don't mind it being off on the full side but want to know for sure when it's empty, for obvious reasons. With it reading too high now (1/2 tank reading with only 4 gallons), I also have a 65 mustang that is the exact opposite, shows empty but actually has about 1/4 tank of fuel. I just don't wanna waste the brain cells trying to calculate from vehicle to vehicle how much gas I really have.

 

... or you can just fill up every 200 miles.

Procrastination, it's not just a job...

 

Shawn,

I have the TPI tech retro style gauges in my 55' I am running a GM tank that is 0-90 Ohms. The TPI's are 240-33. What I ended up doing was taking TPI's sending unit and bolting to the bottom of the huge GM stock sending unit. Drilled two holes and bolted it thru the GM sending unit and wired it up. I drove all year like that last year but I still run into problems when the tank gets about half empty the gauge pegs out to empty. At the point it pegs out I guess watch my odometer because I can go about 390-400 miles off a tank. Please keep us informed on what you get worked out.