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Pontiac Forum: troubleshoot Instrument panel gauges
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Old September 11th, 2017, 09:54 PM
724mula 724mula is offline
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troubleshoot Instrument panel gauges

Hoping someone here can help me troubleshoot my Rally gauges, oil,water and tach do not work, I don't know if the previous owner ever had them working. The IP does have lights blinkers high beam lights working but no gauges. It has a 12 pin plug to the IP is there a trouble shooting that harness and what readings I should get from the pins? The oil pressure gauge goes past 80 when ign. is turned on while the temp gauge does nothing. I have a diagram but it's got to be one of the worst I've ever worked with. Thanks
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Old September 12th, 2017, 10:21 AM
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melsg5 melsg5 is offline
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you need a copy of the factory Pontiac shop manual which typically gives details on diagnosis and wiring diagrams. A guess on your problem would be the printed circuit board on the back of the gauge cluster.
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Old September 13th, 2017, 06:54 AM
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It's a newer printed circuit, I have the shop man, on cd, The gauges are newer also, does some one know what voltage I should be reading at the sender wires for the oil and water at the temp senders with key on not running?
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Old September 13th, 2017, 10:01 AM
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I've never come across a figure for the the voltage at the sender, I would assume 12 volts but the simple test is ground the wire and you should get a full scale reading on the gauge, disconnect the wire and you should get no reading on the gauge.
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Old September 14th, 2017, 07:56 AM
724mula 724mula is offline
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do you know what sender part numbers should be in it? The previous owner say's he thinks he put the right ones in?? the harness to the water temp has a three pin plug which I found he had put a wire spade and wire to the Green terminal and taped off the plug, no power to the green or blue but power to the yellow in the plug, I don't see that harness in the wire schematics so I don;t know how it was wired originally.
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Old September 14th, 2017, 07:58 AM
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Quote:
Originally Posted by melsg5 View Post
I've never come across a figure for the the voltage at the sender, I would assume 12 volts but the simple test is ground the wire and you should get a full scale reading on the gauge, disconnect the wire and you should get no reading on the gauge.
looks like I only have 4.8 volts
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Old September 14th, 2017, 09:38 AM
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looking in the Firebird catalog from www.amesperf.com they show a single post water temp and oil sender for a 72 with gauges. See below what Ames says about the 3 terminal switch, it sounds like you are looking at the wrong one for water temp. Water temp is on the drivers side of the intake.
"For 1970-72, the three-terminal switch toward the passenger
side front is a transducer switch which is not available"
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Old September 14th, 2017, 10:09 AM
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The three wire switch on the passenger side is part of the TCS system explained in chapter 6D of the shop manual. TCS stands for temperature controlled spark. You only get full advance when the engine is up to operating temperature and the transmission is in high gear. The dark blue wire goes to TCS vacuum solenoid. The other two wires go to the firewall bulkhead connector and from there one, pink dbl blk, to the fuse box and the other, dk grn, to the temp light.
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Old September 14th, 2017, 10:57 AM
724mula 724mula is offline
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Ah, Ok it's always fun trying to figure out what other guys have done to wiring, so I guess I'll look for a different dark green wire on the driver side, fun stuff . This car has gauges so your saying the green wire in the TCS would have went to a temp light and I suspect it would not get a signal unless hooked through the TCS? so I may have to try and figure out how to make this work. I'm not sure if the car had original lights or gauges. Thank You!
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Old September 14th, 2017, 11:48 AM
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you can get a copy of the original factory invoice from www.phs-online.com for a fee. That document would tell you if the optional gauge package was originally ordered. From the diagram I see in the 1970 hard copy manual, should be the same for 72, the dark green wire would only have power when hooked to the TCS temp sender. Do you see two senders one on each side of the intake?
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