temp guage troubleshooting

I'm trying to get my temp guage to work in my 66 f100 and I'm not making any progess. I put a hot lead to the wire and the guage sweeps. I put a new sending unit in and its not working. Put 12v to it and it still sweeps. What should be my next step?

 

bump

 

You do know that Ford uses a voltage regulator in their gauge wiring ? Ford gauges operater on about 5 volts and if you are putting 12V to the gauge directly it will not read right. The Volt reg is about 1X2 inches and normaly mounts on the back of the gauge cluster.

 

I forgot to ad, thats new too.

 

Put 4.5 volts directly to the gauge, 3 AA or similar batteries in series will give you that. The gauge should sweep all the way.
If it doesn't, gauge is faulty.


Put 12v to CVR (constant Voltage Regulator) and measure the output as 4.5 or 5 volts.

Check sender, if it is sealed with Teflon tape or similar, you'll have a poor ground.
Use ohm meter to check resistance from base/ground/threads of sender and battery terminal/ground.
Should read as a dead short. That's a good ground between senders base, intake, motor, battery.
You can temporarily ground the base/threads of the sender to the battery terminal to check/insure ground and then apply voltages to sender and gauge while observing output.

The ground between the threads/base of the sender and the battery can be interrupted by things like sealants, (intake manifold) gaskets, goop on threads of bolts and/or sender.


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Many times, a new part such as a sender may be bad out of the box....
Food for thought.


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I heard of a guy that had a faulty gas gauge. No matter what he tried it would only read 1/2 full. Was about to bend the float arm and someone told him he should fill the gas tank. I guess you are getting hot water to the sending unit.

 

The gauge, when voltage regulated, should respond I'm the 78-10 OHM range. Check the sender resistance to ground. Then work your way up.

 

try adding an extra ground wire to the gauge, if i remember right yours grounds thru the gauge cluster from the factory

 

Take off the sending unit wire and ground it, gauge will peg if all is well. Don't leave it grounded long, as this is hard on the voltage regulater.

 

Slickhale, the gauge is thermal and, thus, does not ground through the mount plate or cluster. The sending unit IS grounded.

 

you are correct sir- i need gl***es i guess, i swore the thread said fuel gauge.

 

All of the King Seely brand gauges in the Ford products (and others) are the thermal type. Unless its the early hydrostatic (tell-tale) temp gauges.