[Goatroper50]

My '65 gas gauge shows 3/4 full when the tank is full. It is a new tank and sending unit that was on it when I purchased the car. Can I ground a sending unit wire to see if the gauge will sweep to the full or over full mark which would indicate to me that the gauge is capable of going that far? The tank is empty and out of the car at the moment and I can remove the sending unit. Is there a way to measure the resistance from the empty to full position of the float to see if the unit is not reading correctly even tho it's new? Any input would be appreciated.

[Bill Hanlon]

I think (but am not sure) that Pontiac had changed to a zero ohms empty, 90 ohms full by 1965. Earlier systems were 30 ohms full.

In either case, remove the wire from the sending unit, but leave the gas gauge end of the wire attached.
Turn on the key.

Touch the sending unit end of the wire to ground. The gauge should read empty.

Let the sending end of the wire dangle in free space. The gauge should read full.

If both are correct the wiring and the gauge are good.

If you have an ohm meter you can measure ohms with one meter lead on the post of the sending unit and the other lead on the mount of the sending unit. Should read zero ohms when the float is all the way down, about 45 ohms with the flot half way up and 90 ohms with the float "full".

[Goatroper50]

Thanks Bill. As the tank is out, the sending unit lead was dangling and when I connected the battery, the gas gauge needle went up to full from 1/4 full tank which is where it was when I disconnected the battery. I'll assume that if the sending wire is grounded the gauge would read empty. I'll have to wait til the wife gets home to watch the gauge while I go under and ground the wire. Like you said, if that shows empty, the gauge has to be good. I'll pop out the tank sending unit and run the resistance numbers. Thanks again for your reply.