I have replace all of the wiring on my 300 (thought it was a good idea at the time, but not sure now!) and still having problems with the fuel gauge reading. Before I tear it all apart I wanted to get an idea how it works or what to expect. Normally I expect a 12 v power going into the unit, a wire to the tank, where there id a resistance to tell me if the tank is full. I have the gauge, a printed circuit, a 3 prong plug, a 5 pin plug where there are only 3 being used; the black wire is the power, blue goes to the tank and the third is for the turning signal. Where do I start?
1970 300 fuel gauge
- Thread starter Waggy
- Start date
jorkkeri72
New Member
is there a voltage regulator?
MrMoparCHP
Old Man with a Hat
Does the gauge have 2 studs or 3?
Alan
Alan
There is a 5 volt Voltage limiter
If you have an instrument cluster regulator, sometimes the contacts get corroded and the high resistance will cause the fuel gauge to read low. The regulator plugs into the back of the cluster circuit board on most models and can be removed for service. If you are careful, you can remove the cover of the regulator and use a point file to clean up the contact set.
The cluster regulator feeds constant voltage to the tank unit, if it is functioning properly, you can hook a test light to the wire going to the sending unit in the tank after you remove the wire from the sending unit, you should get a test light that blinks on and off. If the test light does not blink, the circuit is open or the cluster regulator is bad.
Modern oxygenated fuels eventually eat up the brass float in the tank sending unit by degrading the solder joint. This will cause the float to fill with fuel and stay on the bottom of the tank for a permanent "empty" reading.
Many of the repop tank sending units produced overseas are defective because they have the wrong resistance wire installed in the unit which produces an inaccurate gauge reading, if that is the case, you got screwed and will need a functioning replacement.
Dave
The cluster regulator feeds constant voltage to the tank unit, if it is functioning properly, you can hook a test light to the wire going to the sending unit in the tank after you remove the wire from the sending unit, you should get a test light that blinks on and off. If the test light does not blink, the circuit is open or the cluster regulator is bad.
Modern oxygenated fuels eventually eat up the brass float in the tank sending unit by degrading the solder joint. This will cause the float to fill with fuel and stay on the bottom of the tank for a permanent "empty" reading.
Many of the repop tank sending units produced overseas are defective because they have the wrong resistance wire installed in the unit which produces an inaccurate gauge reading, if that is the case, you got screwed and will need a functioning replacement.
Dave
2 studs
MrMoparCHP
Old Man with a Hat
I got it working! Had to take the dash out. I compared it to the other used one I had, checked all the parts and took the best of both, cleaned them and put them back. It works!
Thanks for the advice! It is great to have a place to go to "talk" with others about the problems you run into with old cars!
Thanks for the advice! It is great to have a place to go to "talk" with others about the problems you run into with old cars!
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