method to check instrument voltage regulator

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   I have my instrument cluster out of my 70 AMX and I wondered if anyone had a way to test the instrument voltage regulator? The service manual has a method for testing in the car using a spare fuel sending unit. I know it supplies a constant 5 volts to the gauges. It has 3 prongs that push into the back of the instrument cluster. Would anyone know which ones would be 12 volts in and 5 volts out? I have a known good old regulator and a new regulator and they both have different resistance readings? This dash is such a pain in the as  to take apart that I'd like to test before I reassemble. As always any information is greatly appreciated.Thanks,
-Bernie

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bvpotash1 Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Nut Joined: Apr/02/2010 Location: Syracuse NY Status: Offline Points: 306	Post Options Post Reply Quote bvpotash1 Report Post Thanks(0) Quote Reply Topic: method to check instrument voltage regulator Posted: Dec/01/2019 at 11:58am
	I have my instrument cluster out of my 70 AMX and I wondered if anyone had a way to test the instrument voltage regulator? The service manual has a method for testing in the car using a spare fuel sending unit. I know it supplies a constant 5 volts to the gauges. It has 3 prongs that push into the back of the instrument cluster. Would anyone know which ones would be 12 volts in and 5 volts out? I have a known good old regulator and a new regulator and they both have different resistance readings? This dash is such a pain in the as to take apart that I'd like to test before I reassemble. As always any information is greatly appreciated. Thanks, -Bernie

george w Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jan/27/2013 Location: New Jersey Status: Offline Points: 2899	Post Options Post Reply Quote george w Report Post Thanks(0) Quote Reply Posted: Dec/01/2019 at 12:08pm
	The original IVR does not produce a constant 5 volts out. It produces a pulsed on/off/on/off, etc. 12 volts out that averages out to 5 volts. It uses a heating element with a bimetallic arm and a pair of contact points. If you're getting a resistance reading between two of the contacts then you're likely reading the heating element. Since this type of IVR was used on many American cars of this period you can probably find the terminal assignments on the internet. I'm sure the case is the - side or the ground side.
	Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.

bigbad69 Members Profile Send Private Message Find Members Posts Add to Buddy List Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6668	Post Options Post Reply Quote bigbad69 Report Post Thanks(0) Quote Reply Posted: Dec/01/2019 at 2:58pm
	The IVR also requires a load to make it operate. It is the current running through it which causes it to heat up, thereby opening and closing the switch. Without a load, if you hook up 12V to the input to test it, you will get a constant 12V out of it. A spare gauge would provide a load, or you could substitute the gauge with a 10 ohm resistor (it would need to be a 3Watt or better rating to survive the test).
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tomj Members Profile Send Private Message Find Members Posts Add to Buddy List AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7544	Post Options Post Reply Quote tomj Report Post Thanks(0) Quote Reply Posted: Dec/01/2019 at 8:28pm
	probably easier to power up the whole panel and test that way.
	1960 Rambler Super two-door wagon, OHV auto 1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com