And this one helps with low reading dash gauges:
Improving the Instrument Panel Ground
The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release ****. The screw will have either a ¼" or 5/16" head on it.
This ground point is responsible for handling the ground circuit for the following items: Dome lamps, Seatbelt and key warning, trans comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things.
The problem is that where the ground point is located does not have a good contact with the chassis where the ground should be. The solution is simple.
Make up a jumper wire with #10 gauge wire about 10" long. On one end, crimp on a ¼" round wire terminal. On the other end, crimp on a 3/8" round wire terminal.
Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other.
Look above the driver’s side plastic kick panel just forward of the top of the hood release ****. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely.
**Special note for Comanche owners: Make your jumper wire 12" long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.**
　
Revised 11-29-2011

 

I also have this same problem . But the battery volts at battery drop down to 11.68 or so . This problem seems to be worse in the winter time which it is here now in iowa . I would really like to get this fixed . I drive one way 40 miles to my work . The gauge goes down to the read about 9 volts . I have done all the renix ground fixes to no help . New battery new starter relay 2 new alternators. Bigger wire from alt to starter realy to battery . This thing is really making me made . This is a 1990 jeep cherokee . Need help please ! Thanks,Brad

 

Might try what's outlined in post 16^^.

 

I also have a '90 and my volt gauge always read low, in fact one day I just flat died. Did all the ground refreshes, added the dash ground but no change. Finally pulled the gauge cluster and cleaned ALL the contact / connection pads and now the volt gauge reads good.

 

Not a bad idea. A comparison can be made between actual battery voltage and what teh gauge reads by using a hand-held voltmeter at the battery.

 

After doing all recommended tricks mine ended up being fuse issue .Installed a circuit breaker in its slot problem solved. Buy cheap fuses has its draw backs.

 

Which fuse?

 

Guage one ....

 

I'm having a very similar problem. I have a new battery (that has been recently tested again) and the alternator has tested fine several times from different testers. What is different about my symptoms (on my 91 Cherokee) is that sometimes, when the guage shows to be around 11 volts, it will come back up to over 14 and stay there as long as the engine is running. And, say on the way to work, it will do this in nearly the same spot each time, no matter how long I've warmed it up prior to leaving for work). At night, with lights on, it has died completely (as well as during the day with no lights on when this charging problem has challenged the battery and I've had to recharge it with a box). Also, if at only 11 ish when started, the "check engine" light is on, but if starts at 14 it is not. If it starts at 11ish and then comes back up to 14, that light doesn't go off. So, it acts sort of like a short, but only goes one way - UP. I replace the pertinent fuses in the box under the hood, as suggest on some of the forums here, but that didn't do it. Given my symptoms, it doesn't sound like it could be any other "connection" problem, unless when sufficiently warm the problem is circumvented some how. I did replace the belt this past summer, but it feels tight enough to me and to others. I did read on some post that there is a fuse in the under-the-dash box that is related to charging, but I couldn't see it at first look.

Help please!!!

 

If I remember right this was covered in a thread last year where someone brought up that everything runs through the starter relay before heading out. I remember my volts showed low at the gauge and cigarette lighter as I turn things on but I still had 14-15v at the battery running and off the battery is fully charged. The idea was that the dash was last in line to get voltage and that was why it has a habit of reading low.
I ran a jumper wire(since removed) to the gauge and it worked properly. I only worry if it spikes over 14 or drops below into the red.

 

"The idea was that the dash was last in line to get voltage and that was why it has a habit of reading low."

Yeah, but the engine actually has died, so it isn't just a guage reading problem (unless the guage tells the engine what to do rather than the other way around). And the headlights will dim and all of that too, so it's got to be a charging proplem -something is blocking the charge getting back to the battery, and when that something goes away, all is restored in a matter of seconds (but isn't "instantaneous"). Wierd.

 

Sounds like something is pulling more juice than it should? Backtrack relays; starter relay, ignition switch(on top of the column), headlight switch, relays in general,short in starter.
All of these items especially the ignition and headlight it seems will pull more than they should when they are shorting or burning up, and will cause the motor to die, Could be what's wrong?

 

Highmileage, I should have mentioned that I've long suspected something like this, but didn't remember everything with my first post. In or out of the car, I can hear a slightly high-pitched (what I think as an) "electrical hum" that seems to be coming from the rear of the car, and at times when that sound goes away, it coincides with the voltage returning to normal. But the cessation of this sound doesn't always mean that it returns to normal, at least while in my driveway. But, I've long suspected my fuel pump, as this seems like the only thing in the rear that could pull enough power like that - yet I seem to have no "related" fuel or driving issues when this sound comes and goes. It's just when it stops, my battery gauge and electrical power returns. Can you have your fuel pump tested, whilst still on the car? I don't have the time or the money to spend on a lot of trial and error, professional mechanic diagnosis, spending money to test this or that. Yet I know I have to find and fix the problem, or I'll have too much down-time, which I can't afford either.

Is there something else in the back or under the car that might do this?

Thank you for your suggestions (hm)!

 

The noise/hum is the electric fuel pump inside the fuel tank.

 

Cruiser54: Thank you for your post. Can the fuelpump make this noise, pull extra power enough to cause charging problems), and still not have any at-that-moment-fuel-related issues?