My name's Dan. Although my career has been in the motorcycle industry, I have spent my life doing all types of motor vehicle diagnosis, repair and modification. I do light machine work, fabrication, welding and electrical diagnosis/repairs. I owned and operated my own motorcycle dealership from 1979 to 1994. Raced off road race cars from 1995 to 1997, then started my second career at YamahaI Motor Corp. USA and retired in April 2019 after a 22 year there. I was in charge of technical service and developed all the technical procedures and technical bulletins for motorcycle products. Since retirement, I've been keeping busy with some fun projects, such as restoration of a 1964 Valiant, various machine work projects (I have a lathe, drill press/mill table, welding equipment and a press. Most recently, I'm restoring a meter cluster for a neighbors 1960 Oldsmobile 88. Thought this would be a good place if I have a question, which I do. It appears the fuel gauge operates on a 0~30 ohm variable ground (sending unit) and is powered by 12V+ when the ignition is turned on. The two gauges I have will both go immediately to empty even with 500 ohms resistance on ground (brown) when powered 12+ on pink. They will also only read 2/3 full when unpowered and I'm assuming they should read full when unpowered. Can anyone chime in?

 

Welcome to the site. You are correct, 0-30 ohms on the ground side with 12v power with the key on operates the fuel gauge. It also requires a chassis ground to the case I believe to work correctly.

 

If anyone has a 1960 88, does the fuel gauge normally go to the full position when the ignition is switched to off?

 

Thanks. I have the housing grounded. the pink (12+) connected to a battery and the brown (sender wire) connected to to ground thru a 0~500 ohm potentiometer. Even with 500 ohms, the needle is still pulled to full. The two gauges I have when upright and level will only go to 2/3 full without power. My understanding they should go to full with no power and when powered, get pulled to empty as the resistance is lowered from 30 ohms (full) to 0 ohms (empty). Sound right? If so I suspect both gauges are bad, but that's odd.

 

You wouldn't by chance know the resistance of those coils in the gauge by chance, would you?

 

Don't remember what my folks' Sixty did but I had a 1960 Chevrolet that it went to E with key off. Circuit design changed in I think 1965.

 

Maybe I don’t understand completely, but I’m not sure why you expect something different. You said the sender will show Full with 30 Ohms, so 500 is over 10x past full.

 

I merged your 2 threads. There is no rest position for the fuel gauge when the system is powered off. It will move to some arbitrary position depending on the last level it showed.

 

BINGO, we have a winner! Now if the gauge stayed at full when the sender wire is grounded (0 ohms), then we'd have a problem.

 

The gauge needs to be powered at all times for the reading to be meaningful. The needle position when unpowered is random and meaningless.
With the wire to the sender grounded, the gauge should read EMPTY. With the wire to the sender not connected to anything (which is infinite resistance), it should read FULL. If the gauge behaves this way it is working correctly. As noted 500 ohms is much greater than 30, so obviously it should still read FULL. Any resistance greater than 30 ohms should read FULL.

 

Fun71....No, you understand. That was a redundant statement on my part.