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66 temp guage not working

Kooter

Member
the temp guage on my 66 isn't working. All others are. Took the wire off the sending unit and grounded it out and got no response from the guage. Checked continuity on the wires one the engine bay and under the dash they were reading 1.4ohms but it was fluctuating. Pulled the cluster out and found nothing out of the ordinary. Pulled both wires off the temp guage and hooked up a new guage and ran a single wire to the sending unit and connected it to the temp guage. Started the car and still had no movement on the new guage. Not sure where to go next. I wouldn't think it is the voltage regulator since the other gauges work normally.
 
Resistance shouldn't fluctuate. 1.4 ohms is not enough to cause the gauge not to work. I've found that the 90* connectors for the gauges, which are ganged in-line, often have high resistance due to years of being under strain. Straighten out the wire from the 90* connector and tug moderately hard; sometimes that clears things up.
 
I will check that on Wednesday when I have off. How would I test that black and green wire to see if I have enough volts coming through? I am assuming ignition on or car running?
 
Key to ACC, use voltmeter positive to black/green wire, negative to chassis ground; voltage should fluctuate wildly on a digital meter, somewhat steady at 5V on an old analog meter. If you see zero voltage and steady at zero, then there may be a broken wire somewhere.
 
You sure oil and fuel gauges are working? If so, it is undoubtedly a bad wire, as all three gauges are tied into the same cvr output line. There's a male spade that plugs into the cvr and has two wires going out of it: one to the oil and then on to the fuel gauge; the second wire crosses over through the underdash harness to the water temperature gauge. I've seen wires break at the back of the CVR input molded connector, but it is rare.
 
Now your making me question weather the other two are actually working. Aren't all the gauges supposed to do a full sweep when the key is put into the acc position? I don't remember if they did or not before I took the dash out this afternoon. It appears to be the original voltage regulator in the cluster so maybe it is bad
 
No, they do not do a full sweep when power is applied; that's only on newer vehicles. Put the key to ACC, and watch your gas gauge. I hope you have gas in the tank. Start the car: does the oil gauge register at all? If fuel and oil don't move, then you have a bad CVR or a bad ground to the CVR.
 
I'm 90% sure the gas guage moves. Oil I'm 75%. I am think I will will have some free time tomorrow to install the cluster and verify.

Is there any checks I should do before installing the cluster. I wasn't sure if the black green wire was all connected from one side of the cluster to the other to do a continuity check. It looked like it split off on the schematic and I only know enough about electrons to get myself in trouble.
 
You can check continuity between the 3 90* black/green sockets and the one male spade.
 
I have continuity between all gauges. I do not have continuity between the blk/grn wire (30C) that connects on the driver side of the voltage regulator and the blk/grn wire of the gauges. Not sure if I'm supposed to. On the schematic it looks like two separate wires. I did find a crack in the shielding of this blk/grn wire that may be my problem. Thoughts?
 
I have continuity between all gauges. I do not have continuity between the blk/grn wire (30C) that connects on the driver side of the voltage regulator and the blk/grn wire of the gauges. Not sure if I'm supposed to. On the schematic it looks like two separate wires. I did find a crack in the shielding of this blk/grn wire that may be my problem. Thoughts?
There are two distinct systems that are both black/green. One has a female spade connector (goes to CVR input; it is ACC power) and the CVR output is also black/green. The output has a male spade and three 90* slip-on connectors. Are you saying that all 3 90* connectors have continuity? If so, that's good. Are you saying that these three connectors have no continuity to the female spade connector? That is good, so long as everything was disconnected from the CVR.

Do any of the gauges actually move? That is your next test to perform. It could be that the CVR is not putting out power because it isn't properly grounded or is broken. The second test is to disconnect one of the 90* slip-on connectors and test for voltage when the key is in ACC.
 
Started car. Fuel and oil gauges move. When checking volts on the grn/blk wire of the temp guage I get voltage but it is all,over the place. My fluke flashes all sorts of numbers. .841,.041, .002, then 0.L then more random numbers. Each time I check voltage I get different numbers. I also have to find a sweet spot in the connector to get any reading making me think it is the 90 degree connector that it is bad.
 
Voltage fluctuations are expected from the output of the CVR due to the nature of the signals. Now measure the resistance between the two posts of the temperature gauge. You should see something like 13-20 ohms. Anything in the kilo- to mega-ohm range indicates the gauge is bad.
 
Guage tested bad. Swapped out the guage with a different one. Tomorrow I should have more time to install cluster and test it out. Thanks for your help thus far
 
Finally done getting the dash put back together. The dam guage still wasn't working. However this time when I grounded out the wire to the temp sending unit the guage did a full sweep. Ran to the parts store to get a new sending unit and left the key on which drained the battery. So now I am waiting for it to charge to see if the new temp sending unit is actually good.
 
I hope you got the right sending unit (for gauges), as the version for indicator lamps won't register correctly on the gauge. For 1966 Mustangs, only the gauge version is used.
 
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