- Joined
- Jan 1, 2002
- Messages
- 7,246
- Location
- Washington, Michigan
- Corvette
- '67 Marina Blue Convertible
OK, try this, in the sequence described:
1. Check the "S" terminal (pink wire) at the gauge with the key on (with a voltmeter, not a test light) to make sure you have a full 12 volts there (power to the gauge).
2. Check the (pink wire) terminal at the sending unit with the key on (with the voltmeter) to make sure you have a full 12 volts there (power to the sending unit).
3. Turn the key off.
4. Disconnect the tan wire from the sender (note the terminal it comes off of so you don't inadvertently reverse the connections for the tan wire and pink wire), and turn the key on. The gauge should peg to full (infinite resistance). Now use a jumper to ground the still-disconnected tan wire terminal to a good clean frame ground, and the gauge should deflect to empty (zero resistance); if the gauge doesn't peg to full and empty with this test, there's a gauge problem. If it passes these two tests, the gauge and the tan wire from the sender to the gauge are both good.
5. Turn the key off.
6. Remove the black ground connector from the sender and use a VOM to check between the end of that wire and a good clean ground on the frame; you should show zero ohms. If you don't, there's a problem in that ground circuit, which runs forward through the body harness and the multiple connector above the driver's side kickpad where it connects to the instrument panel harness, and finally grounds through the black pigtail that comes out of the 3-cavity radio connector and screws to the bottom of the dash cross-brace with a star washer (this one point grounds EVERYTHING at the rear of the car, including the dome light).
7. If everything checks OK to this point, it's time to check the sending unit. Disconnect all three wires at the sender, and connect a VOM to the two pin terminals on the sender (12V power and gauge terminals). Work the float up and down, and the VOM should read zero ohms with the float all the way down (empty), and 90 ohms with the float all the way up (full), with a smooth, linear progression between the extremes. Apply light sideways pressure to the float arm while doing this to see if the readings change; if the wiper connected to the arm inside the resistor housing on the sender has inadequate tension as it traverses along the wirewound resistor, it can "skip" and show flaky readings.
8. If all these tests are passed and you still get flaky readings, take two aspirin and don't call me in the morning :W
Trivia: The C2 fuel gauge system is a 3-wire powered Whetstone bridge circuit, that was never used on any other GM car except mid-60's Cadillacs; an "experiment", if you will. They went back to the conventional 2-wire non-powered system used on every other GM car in 1968; so much for the "experiment" :eyerole .
1. Check the "S" terminal (pink wire) at the gauge with the key on (with a voltmeter, not a test light) to make sure you have a full 12 volts there (power to the gauge).
2. Check the (pink wire) terminal at the sending unit with the key on (with the voltmeter) to make sure you have a full 12 volts there (power to the sending unit).
3. Turn the key off.
4. Disconnect the tan wire from the sender (note the terminal it comes off of so you don't inadvertently reverse the connections for the tan wire and pink wire), and turn the key on. The gauge should peg to full (infinite resistance). Now use a jumper to ground the still-disconnected tan wire terminal to a good clean frame ground, and the gauge should deflect to empty (zero resistance); if the gauge doesn't peg to full and empty with this test, there's a gauge problem. If it passes these two tests, the gauge and the tan wire from the sender to the gauge are both good.
5. Turn the key off.
6. Remove the black ground connector from the sender and use a VOM to check between the end of that wire and a good clean ground on the frame; you should show zero ohms. If you don't, there's a problem in that ground circuit, which runs forward through the body harness and the multiple connector above the driver's side kickpad where it connects to the instrument panel harness, and finally grounds through the black pigtail that comes out of the 3-cavity radio connector and screws to the bottom of the dash cross-brace with a star washer (this one point grounds EVERYTHING at the rear of the car, including the dome light).
7. If everything checks OK to this point, it's time to check the sending unit. Disconnect all three wires at the sender, and connect a VOM to the two pin terminals on the sender (12V power and gauge terminals). Work the float up and down, and the VOM should read zero ohms with the float all the way down (empty), and 90 ohms with the float all the way up (full), with a smooth, linear progression between the extremes. Apply light sideways pressure to the float arm while doing this to see if the readings change; if the wiper connected to the arm inside the resistor housing on the sender has inadequate tension as it traverses along the wirewound resistor, it can "skip" and show flaky readings.
8. If all these tests are passed and you still get flaky readings, take two aspirin and don't call me in the morning :W
Trivia: The C2 fuel gauge system is a 3-wire powered Whetstone bridge circuit, that was never used on any other GM car except mid-60's Cadillacs; an "experiment", if you will. They went back to the conventional 2-wire non-powered system used on every other GM car in 1968; so much for the "experiment" :eyerole .
Okay I like John's post...
can analyze the results of #4 above.
