Voltmeter - reading low??

Hey guys & gals. Got a Q about my 88 MJ, 4.0, AW4, 4x4

My dash volt meter reads low...like 10 or 11V when running with no lights on or accessories turned on. When I turn on an accessory it blips just a hair, when I have the light on and an accessory (lights, fan, etc.) it rides right about the same spot.

After running on the highway for awhile it seems to recover and rides just below straight up.

When I check it at the battery with my DMM it reads 14.2 or so, idling. When off it reads 12.5 or so.

All of my accessories (fog lights, driving lights, camper lighting) are wired with relays powered through one 40A fuse. When I pull the main fuse for the relays the dash meter reads just as it does with it in.

All grounds are recently re-refreshed, C101 is cleaned, greased and tight. Fuse block is cleaned up and tidy. Where does the dash meter get it's information. Do you think it's just a funky gauge...or ??

The path is red wire into ignition switch direct from a fusible link, yellow wire out of the ignition switch to the fuse block, through the gauges fuse. Do a sample voltage test at these points. If your voltage out of the fuse, into and out of the ignition switch is good, it will tell you if it is the gauge or possibly the contact strip to the gauge cluster may be the problem. There is a TSB about the contact strip to the gauge cluster, it is prone to oxidation. Same power source for all the gauges, they share a bus.

It is either a funky gauge or there is resistance someplace in the circuit.

Ground would be a good place to look. If you are getting good voltage out of the gauges fuse, my next stop would be the ground. Quote from Cruiser "There is the ground to the lower diagonal dash brace to the left of the steering column ". This ground, through splices and whatnot is ground for at least a dozen different things.

ParadiseXJ said:

Hey guys & gals. Got a Q about my 88 MJ, 4.0, AW4, 4x4

My dash volt meter reads low...like 10 or 11V when running with no lights on or accessories turned on. When I turn on an accessory it blips just a hair, when I have the light on and an accessory (lights, fan, etc.) it rides right about the same spot.

After running on the highway for awhile it seems to recover and rides just below straight up.

When I check it at the battery with my DMM it reads 14.2 or so, idling. When off it reads 12.5 or so.

All of my accessories (fog lights, driving lights, camper lighting) are wired with relays powered through one 40A fuse. When I pull the main fuse for the relays the dash meter reads just as it does with it in.

All grounds are recently re-refreshed, C101 is cleaned, greased and tight. Fuse block is cleaned up and tidy. Where does the dash meter get it's information. Do you think it's just a funky gauge...or ??

Click to expand...

The IP voltmeter - especially on RENIX - is a notorious liar.

I stopped paying attention to the "absolute" reading years ago; instead, I just make grease pencil marks once I confirm the readings with my independent meter. It's easier.

When I get around to redoing the dashboard, I'll put in a PROPER voltmeter - until then, grease pencil marks it is...

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 knob. 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 knob. 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

Paradise: PM me your email address if you want a photo.

Also, if you haven't upgraded your cables to Jon's (5-90), it would be good to do. At a bare minimum, upgrade them per my ground refreshing write-up.

Same thing happened to my 88 XJ last week. Cleaning the ground going to the bell housing fixed it

I thought for sure Paradise had already done the ground refreshing though. Have you, Paradise?

cruiser54 said:

I thought for sure Paradise had already done the ground refreshing though. Have you, Paradise?

Click to expand...

Yes, I did an over all refresh of all electrical connectors as a matter of course when I got the Jeep before I ever really knew what to refresh.

I cleaned and re-furb'd the C101 about a year ago when I first ran across your "Mostly Renix Tips". I have a 4 gauge cable from block to firewall (instead of the flat braided grease catcher), an aux ground from battery to fender and I upgraded the dash ground and cluster connections in June. I also did the overall ground refresh and unplugged, cleaned, greased as many of the connectors under the hood as I could reasonably do while the engine was down for the head gasket job.

The engine runs great, lots of power, smooth idle. All electrical components work fine.

ParadiseXJ said:

Yes, I did an over all refresh of all electrical connectors as a matter of course when I got the Jeep before I ever really knew what to refresh.

I cleaned and re-furb'd the C101 about a year ago when I first ran across your "Mostly Renix Tips". I have a 4 gauge cable from block to firewall (instead of the flat braided grease catcher), an aux ground from battery to fender and I upgraded the dash ground and cluster connections in June. I also did the overall ground refresh and unplugged, cleaned, greased as many of the connectors under the hood as I could reasonably do while the engine was down for the head gasket job.

The engine runs great, lots of power, smooth idle. All electrical components work fine.

Click to expand...

I figured you had.

The adding of the IP ground may make a difference.