fuel and temp gauges?

[fordman]

take the wire off of the sending unit and put it to ground and see if the gauge moves. i think that is how its done.

[hotrod ford]

i did that just now and it did not move.

[hotrod ford]

i read on a trubleshooting sight just now and it says i might have a short somewhere. both gauges did read the same. the lights work and the fuel reads 1/4 of a tank. tomorrow i'm going to get a new temp and oil pressure sensor just to eliminate those out of the problem. then we will see from there.

[70_F100]

If you can't get them to move by grounding the wire to the sender, the trouble isn't in the sender.

Don't waste your money. That won't fix it!!!

[hotrod ford]

alright then, how am i supposed to ground it to the sender if it is already grounded? if the unit is bad nhow will the needle move at all. i have read on other post you have to ground the wire to the eng and if it moves it will be the sender that is bad. i do not understand what you are saying about grounding it to the sender.

[70_F100]

Maybe I phrased it wrong.

Remove the wire from the sender.

Hold that wire to a ground. Easy way is to stick a small screw into the terminal, approximately the same size as the threaded stud on the sender. You should be able to touch it to any bare metal part on the engine (coil bracket, carb, etc.) and make a ground. This should make your dash gauge move.

The sender is nothing but a variable resistor. When the engine is cold, there is no continuity between the stud and ground (through the sender). As the engine warms up, resistance changes and allows an increasingly stronger circuit to ground (again, through the sender).

Touching the wire directly to ground has the same effect on the gauge as if the engine was extremely hot. Removing the wire from the sender and holding it in your hand emulates a cold engine.

Another way to look at it is that the sender is the link that completes the circuit. A complete circuit requires a power source and a load. Open circuit, no flow of electricity. Think of it this way. If you remove the negative battery cable, your electrical system is not a complete circuit. Nothing will work. No lights, no wipers, no starter. Open circuit (in terms of what we're discussing, cold engine, temp gauge reads "cold"). Put the battery cable back on, you complete the circuit. Lights, wipers, starter work as they should. Closed circuit (in terms of the temp gauge, "hot").

Does it make sense now?

[fordman]

so then his gauge or wiring would be bad one of the two. if he tested it right? so then he could put power just to that gauge only and ground the other side and it should work. if it didnt then the gauge would be bad. but if it did work it would be the wiring?

[hotrod ford]

ok, there was one thing i did not check. it was how the wiring was on the engine itself. i put the screw in the temp sensor terminal and nothing happened. if i would of had looked at the oil pressure gauge i would have noticed it move. so when i had my wife look at the gauges when i made a ground she saw the gauges move. the oil pressure and the temp wires were crossed. anyway the gauges work but still found out that the sensors are still bad. thanks for the help and your patience. HRF