Gjeep Posted October 6, 2018 Share Posted October 6, 2018 I'm putting my 92 MJ back together. Just about everything is new. New battery, mopar alternator, etc. The Gauge is negative in the red though it's running fine. Confirmed all wires connected. All other gauges read properly. Any ideas? Link to comment Share on other sites More sharing options...
hakukamana Posted October 6, 2018 Share Posted October 6, 2018 Check your instrument cluster ground. Is your alternator case grounded? Is your alternator plug a two wire or a three wire? The two wire is usually one wire triggers the voltage guage, the other is for an AC feed. Have you checked your battery for voltage while the truck is running? Should be 14.+ Do it with a DVOM The last thing I would say is I have a 93' YJ and had a similar issue, it was the charging circuit in the ECU, sent it off to have the circuit rebuilt or so the rebuilder claimed, got it back hooked it up and "POOF" in a cloud of smoke the ECU fried. If you find it is the ECU don't waste your money on trying to have it rebuilt. Find a similar year, engine, and transmission combination from a donor and replace it. It will be cheaper in the long run. Link to comment Share on other sites More sharing options...
Eagle Posted October 6, 2018 Share Posted October 6, 2018 Since the lowest reading on the gauge is +9 volts, I doubt very much it's in the negative. The red zone runs from +9 to +11. What number is it reading? If you put a voltmeter across the battery terminals, what does it read with the engine off, and what does it read with the engine running? Link to comment Share on other sites More sharing options...
DirtyComanche Posted October 7, 2018 Share Posted October 7, 2018 The contacts on the circuit board thingy on the cluster will corrode and do that too. But check the ground first. And as said, verify actual voltage with a meter to make sure it is charging correct and whatnot. Link to comment Share on other sites More sharing options...
hakukamana Posted October 7, 2018 Share Posted October 7, 2018 Just a thought, the electrical load from the vehicle will pull the voltage down. It should not pull it down into the red, but lights, blower motor, reverse lights(???) I don't know why?, if you have a short, or a severe load on the electrical circuits in the truck it will pull the voltage meter down from the normal 14 position. The more circuits that are in use the larger the load on the charging system and the battery. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 7, 2018 Share Posted October 7, 2018 8 hours ago, Gjeep said: I'm putting my 92 MJ back together. Just about everything is new. New battery, mopar alternator, etc. The Gauge is negative in the red though it's running fine. Confirmed all wires connected. All other gauges read properly. Any ideas? Are you using the original 92 working cluster that you pulled or did you change any of the gauges out? Could be something as common as a sticking meter movement. Seen a crap-load of those. You can pull the cluster and apply a known direct battery voltage across the VM cluster terminals to check the meter accuracy. But do check the actual charging voltage to the battery, as I'm sure you already know. Link to comment Share on other sites More sharing options...
Gjeep Posted October 7, 2018 Author Share Posted October 7, 2018 I think I may have found the issue. One of the tabs inside the alternator held on by small bolts is broken. The bolt spins...like mentioned above....one wire triggers the voltage gauge, the other is for an AC feed. It must be the tab for the voltage gauge. Brand now Mopar alternator too. Need to swap it out. Link to comment Share on other sites More sharing options...
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