Hey, so today I was doing some things around town and saw that my battery gauge was reading a little above 10 volts. This seemed really strange to me since earlier in the day I was reading 14 volts as I was driving around town. I then stopped the Jeep and checked the voltage at the battery posts and clamps. Both spots has a reading of 14.2 Volts. So my question is, what could cause my gauge to be off? If it helps it is part of the factory gauge cluster.

 

How clean are your terminals?

 

I would think just fine because there was no drop in voltage between the clamps and the posts. but I could take them off, brush them, and put them back on just to see.

 

Check the voltage at the alternator output terminal.

 

so I checked the alternator output post to frame connection and I got a reading of 14.4 volts. I then scuffed the terminal and clamp connections. It did nothing, and so I thought I would see what the voltage at the battery was when I put my aux electric fan on, head lights, defroster, and KC lights. It then read 13.8 volts on my hand held volt-ohm-meter, but in the Jeep it was in the read zone closer to the 9 volt line. Judging off of those tests, it seems that the gauge has a bad connection. But I could be wrong. thoughts?

 

Have you ever refreshed all your grounds?

 

Yep, I just did that. I refreshed each end and pulled the braided ground wire from the back of the motor to frame connection and replaced it with a new cable, pulled apart the connection at the engine post located on the passenger side back portion of the motor (near the oil dipstick tube), and refreshed the connection for the negative post and clamp at the battery. All this was done maybe a month ago.

 

Since everything seems healthy under the hood, it sounds like the gauge.

I would get a cluster from the salvage yard and replace the gauge. Or put up with it reading low.

 

This might help:

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

 

Alright, Ill try re-grounding the grounding wire for the cluster and see if that helps. It was weird today because half way through the day it started working again, and then it went back to the weird old thing. I also may try and pull the cluster out and clean out the electric connector that plugs into it. Maybe some grime got caught up in there. Thanks for all the help! Ill let you guys know what happens after I try these few ideas.

 

See if you notice any other improvements after adding just the ground.
Instrumant panel lights brighter etc.

The grounding point/attachment method for ALL those circuits is certainly crappy by design.