flucuating charging gauge but charging fine

[ratrapp]

on my 88 mj the alt. gauge drops alot when you turn the signals on or the heater motor.the gauge actually moves up and down with the signals as they blink. i checked the battery voltage at the battery it self and it's rock solid at 14.5 with everything turned on and dosen't flicker any.i replaced the ground cable off of the battery to the block,no change.i replaced the alt with an ac delco unit and no change.i even bypassed(straight wired)my c101 connector and it hepled alittle but not alot.my old cluster did this alittle before i replaced it with a tach style cluster but not as bad as this one.all of the other gauges work fine(as good as factory gauges work).the truck charges fine but i would like to fix this so if my alt does start going i will know for sure and not be guessing.with no load on the system the gauge reads alittle over 14 volts like it should.it's when you turn the blower or signal lights on is when it acts up.you can turn the headlights on and it doesn't flicker(only turn signals or blower motor).

[Eagle]

You have a volt meter, not an ammeter. A volt meter does NOT show anything about charging rate, it shows the voltage in the system. It is normal for the volt meter to react to sudden changes in load, because the needle reacts before the voltage regulator adjusts. The needle will dip when you turn on the headlights, too, then it'll return to normal when the voltage regulator adapts. With the blinkers, they go on and off fast enough that the voltage regulator can't mask the fluctuation.

 

If you want to see how much your alternator is putting out, you'll have to install an ammeter.

[HOrnbrod]

You have a volt meter, not an ammeter. A volt meter does NOT show anything about charging rate, it shows the voltage in the system.

 

:agree: But the VM shows the voltage in the system at the connection of the + terminal sensing wire relative to ground. On the early HOs (maybe the Renix models too) Chrysler tied this connection at one of the PDC main distribution fuse output terminals so the VM registered every minute voltage drop whenever anything was turned. I changed the VM sensing point connection to one near the battery positive terminal, and it smoothed it out a lot as the battery acts like a surge filter. Later on Chryco did the same thing; that's where I got the idea from. :D

 

Also, the gauges common ground point is a small sheet metal screw up under the dash. I left it there, but ran an addition ground wire to a good body ground behind the left kick panel. This gives all the gauges a better ground reference point.

[ratrapp]

hornbrod,this sounds like what i need.could you go into greater detail about what you did to fix this?thanks

[HOrnbrod]

You need a wiring diagram for your dash circuits (the FSM is best) for your year model. Start at the VM gauge and follow the + terminal out thru the harness/connectors and see where the VM gets the sensing voltage from. Then go from there. I think it's best attached as close the the + battery post as possible to take advantage of the battery's filtering characteristics.

 

The dash ground point is up under the cluster on a sheet metal screw, a 12AWG black wire attached to the dash brace bracket. Make sure this screw is clean and tight, then run another wire from it to a good chassis ground of your choice.

[ratrapp]

looks like thats my new weekend project,many thanks hornbrod

[Eagle]

I probably need to do this on my '88 Cherokee because the voltmeter always reads lower than a multimeter at the battery shows. But ...

 

Remember that even after this upgrade, you STILL have a voltage meter, not an ammeter. It does NOT show you the alternator output, it only shows you the voltage in the system. By the time you see the voltage drop, it will be an indication that the alternator HAS failed, not that it's getting ready to fail.