need help diagnosing instrument gauge
Thread Starter
Melting Slicks
Joined: Jul 1999
Posts: 3,030
Likes: 17
From: White Pine / Dandridge TN
need help diagnosing instrument gauge
I hate playing electrical detective. In my opinion this is one of the least satisfying things to work on. I'm trying to figure out if the oil temp gauge (not oil pressure) is good or bad. I removed the gauge from the car and tested it with 3 D size flashlight batteries. I can make the gauge read all the way to the right or all the way to the left depending on which way I have the positive and negative connected. I then placed the sending unit in hot water but get no reading. I believe the sending unit is good because I purchased a replacement AC Delco unit. I'm not sure what to make of the fact that I can get the needle to move both ways but can't get an actual temp reading. Any thoughts or suggestions???
Does anyone out there with an oil temp gauge know which color resistor is suppose to be on the back side of the gauge? If you look at the back side of the instrument cluster, you will see different color resistors on each of the gauges. My oil temp gauge has a green resistor. I'm wondering if this is the correct resistor for the gauge.
Does anyone out there with an oil temp gauge know which color resistor is suppose to be on the back side of the gauge? If you look at the back side of the instrument cluster, you will see different color resistors on each of the gauges. My oil temp gauge has a green resistor. I'm wondering if this is the correct resistor for the gauge.
Last edited by Frankenvette; Dec 3, 2004 at 11:36 PM.
Race Director
Joined: Sep 2004
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
Originally Posted by Frankenvette
. Any thoughts or suggestions???
I'm wondering if this is the correct resistor for the gauge.
I'm wondering if this is the correct resistor for the gauge.
definitely over myhead but heres some thoughts....doesn't the resistance change in the sending unit based on temp and that translate in to a reaction in the gauge, how do you know the sending unit is good? how did you ground the sending unit when you put it in the water for your test?
Le Mans Master
Joined: Mar 2004
Posts: 7,493
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From: Little Rock AR
Jim,
The gauge gets the 12V in but the ground is through the sending unit. Have someone watch the gauge with the key on and see if grounding out the sender wire at the block causes the gauge to peg back and forth as you ground the wire. If it does, the wiring is fine and the gauge is working right. The sender can be tested in a hot water off the car or on the car. Check the resistance with an Ohm meter between the threads and the wire connector. The resistance will vary over different temperatures. I do not know what the exact resistance will be for you but around 500 Ohms at room temp and maybe only 100 Ohms at boiling would be a possible scenario.
Hope this helps.
-Mark.
The gauge gets the 12V in but the ground is through the sending unit. Have someone watch the gauge with the key on and see if grounding out the sender wire at the block causes the gauge to peg back and forth as you ground the wire. If it does, the wiring is fine and the gauge is working right. The sender can be tested in a hot water off the car or on the car. Check the resistance with an Ohm meter between the threads and the wire connector. The resistance will vary over different temperatures. I do not know what the exact resistance will be for you but around 500 Ohms at room temp and maybe only 100 Ohms at boiling would be a possible scenario.
Hope this helps.
-Mark.
Thread Starter
Melting Slicks
Joined: Jul 1999
Posts: 3,030
Likes: 17
From: White Pine / Dandridge TN
Originally Posted by stingr69
Jim,
The gauge gets the 12V in but the ground is through the sending unit. Have someone watch the gauge with the key on and see if grounding out the sender wire at the block causes the gauge to peg back and forth as you ground the wire. If it does, the wiring is fine and the gauge is working right. The sender can be tested in a hot water off the car or on the car. Check the resistance with an Ohm meter between the threads and the wire connector. The resistance will vary over different temperatures. I do not know what the exact resistance will be for you but around 500 Ohms at room temp and maybe only 100 Ohms at boiling would be a possible scenario.
Hope this helps.
-Mark.
The gauge gets the 12V in but the ground is through the sending unit. Have someone watch the gauge with the key on and see if grounding out the sender wire at the block causes the gauge to peg back and forth as you ground the wire. If it does, the wiring is fine and the gauge is working right. The sender can be tested in a hot water off the car or on the car. Check the resistance with an Ohm meter between the threads and the wire connector. The resistance will vary over different temperatures. I do not know what the exact resistance will be for you but around 500 Ohms at room temp and maybe only 100 Ohms at boiling would be a possible scenario.
Hope this helps.
-Mark.
The gauge does peg when the sender wire is grounded. I did check the ohms, and it did drop when placed in hot water but my values were a lot lower than what you specified. I think at room temp it is around 3 and droped to around .8 when placed in hot water.
