62 Fuel Gauge

[Greg S.]

I removed and sealed the gas tank. After reinstalling the tank the fuel gauge no longer works. While the sender was out, I tested the resistance which was 45 ohms at empty and 410 at full so I am reasonably sure it works as designed. The fuel gauge reads full with the key off and goes to empty with the key in the on (run) position and stays at empty with the tank filled.

I need help diagnosing and correcting the problem. The wiring diagram is fairly simple but I am no electrical wizard. Pink wire from ignition runs to one side of the gauge. Brown wire runs from other side of the gauge to the float side of the sending unit. Black wire runs from the ground side of the sender to ground. So far I have tested for power to the gauge with the key on. It reads 12+ volts. I tested the brown wire terminal at the sender and got 0 volts with the key on. It seems to me it should be 12 volts. So I tested the brown wire at the gauge, with the key turned on, direct to a ground on the engine and still get 0 volts. It seems that power is getting to the gauge but not passing through it. I did not touch the gauge in repairing the tank. Could I have messed up the gauge some how? How can I further diagnose this problem?

Also, for general knowledge, can anyone explain how the change in resistance from the float changes the reading on the gauge?

[Don O'Connell #33101]

Re: 62 Fuel Gauge

Greg,

It seems like your doing all the right stuff trying to solve your problem. I'm certainly not knowledgable on '62s but I'll try and answer your last question.

Ohms law is:

Voltage = Current * Resistance

The assumption here (since I don't have a '62 AIM) is your gas guage is essentially an ammeter (i.e. measures current - with a different wiring configuration it could be a volt meter). So, the voltage is "fixed" at 12 volts, when the float moves and changes its resistance, it is also changing the the current flow through the gauge (resistance goes up, the current flow goes down) and hence the gauge is displaying the current flow (i.e. gas level).

I've seen other posts on replacement Temp sending units not being "calibrated". What that relates to, as in your tank sending unit, you measured it varing from 45 ohms to 400+ ohms. This is what your gauge is "expecting" (i.e. calibrated to). If a replacement unit varies from say 70 ohms to 550 ohms, the gauge reading will be "off" since the current flow would be different for the exact same float level (or in the temp sensor case, the actual temperature).

Hope this litle bit helps.

Don

[G B.]

Try a new sender

Delco still sells new '62 gas tank sending units for about $60. They have a resistance range from 0 to ~30 ohms.

Your dash gauge does not pass 12 volts on to the sending unit. If you shoot 12 volts to a grounded '62 sending unit, even for a second, you will fry the resistance coil inside. Believe me.

[dale pearman]

Re: 62 Fuel Gauge

Sounds like you've inadvertantly fried the temp sending unit. If you connect the lead at the fuel guage on the dash (from the tank) to the wrong terminal on the guage, this will happen! When your car was new it had a small red warning tag on one of the terminals in order to prevent damage. Replace the sending unit (GM calls it a meter) and be careful how tou hook up the wires at the fuel guage.

Good luck'

Dale Pearman

[Greg S.]

Re: 62 Fuel Gauge

Hi Dale greetings from St. Louis

All I did was remove the tank to clean and seal it. The two wires at the tank were disconnected and reconnected the same. None of the dash guage wiring was touched. When the sender was out I checked resistance with an ohmeter with the float raised and lowered. That was the only exposure the sender had to any electrical current. The fuel guage worked before I removed the tank and did not work when it was reinstalled. I don't see how I fried the sender. Is there a way to check the sender to see if it is toast?

[Greg S.]

Re: Try a new sender

Jerry,

The gauge worked when I took the tank out and did not work when I reinstalled the tank. I only removed the two wires at the tank and replaced them at the same locations. When the sender was out of the car I checked resistance with an ohmeter. I may have been off by a decimal place. Maybe it read 4.5 at empty and 41 at full. Anyway, I am not very familiar with using volt/ohmeters. Still, I don't see how I could have fried the sender. Is there a way to test it.

[Dennis M.]

Re: 62 Fuel Gauge

All sounds like good advise, but if think your unit is still good, you may want to double check your ground. If you disconnected the wires and then re-attached them, you may not have a solid ground and thus no circuit. Good luck Dennis

[G B.]

Sender Testing

Greg -

You did it the right way using a multi-meter or volt meter. I guess you have one with a needle and scale rather than the digital type.

Dennis Moore's suggestion is a good one. Play with the sender ground some more. Also remember that the dash gauge body must be grounded through the housing too.

Jerry