Dash Light Question

[RockMJ]

Hey guys, just got a chance to drive the MJ at night for one of the first times and I noticed something strange. I noticed when I hit the brakes there is a moment where the all of the cab lights go dim. Has anyone ever experienced this before and if so, any pointers on fixing it? The only thing ive done recently is add an LED third brake light inline with the brake light wiring. Any chance this could be the issue? Any solutions to fixing it? Thanks in advance and sorry if this has been covered before

 

RockMJ

[RockMJ]

I should probably also note that my voltage meter is always below 14, even when driving. Any chance the alternator just can't keep up? I had planned on replacing it because turning the heat on with the headlights pretty much kills the voltage and it ends up around 10-12. Just a thought and any input is appreciated

 

RockMJ

[camjeep3]

I experience the exact same thing in my truck. lights dim and voltage reading low... i plan on upgrading my alt in the future due to my winch and aux lighting. Not sure if that will fix it or not

[cruiser54]

Try this first:

 

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

[Harley]

Waiting for results......... :popcorn:

[txjeeptx]

Ha, my MJ has always been like that, too. I'll look into the ground, I was just in that area a little while ago to fix the brakelight switch after my WJ brake booster swap.

 

I understand it as the computer controls the alternator(at least it does for HO 4.os) - it decides when and how much the alternator puts out. So, it could be a reason for low system voltage at times. Rather than hijack the thread, I'll post a new question about alternator upgrades after doing some searching.

 

Corrected the misinformation. Couldn't remember, so I was guessin. The Renix-era alternators are internally regulated. Got it straight, now. There is some info out there about upgrading the Renix alternator to a bigger CS144 unit, but it involves replacing the charging lead with a larger wire(lower gauge number wire), and some modification of the mounting brackets, and possible belt length changes.

 

Didin't see in any other posts, but you might want to check the grounds to the tail light wiring and parking lamp wiring. The tail light wiring ground is behind one(or both?) of the tail lights.

[cruiser54]

Ha, my MJ has always been like that. I'll look into the ground, I was just in that area a little while ago to fix the brakelight switch after my WJ brake booster swap.

 

I understand it as the computer controls the alternator(at least it does for Renix-era 4.os) - it decides when and how much the alternator puts out. So, it could be a reason for low system voltage at times. Rather than hijack the thread, I'll post a new question about alternator upgrades after doing some searching.

 

Absolutely incorrect for a Renix. Correct for HO? Renix has an internal regulator inside the alternator.

 

The dash ground is not something to overlook. You'll be surprised how much better things work when you add the wire per the write-up. Read the write-up and see how many things are relying on that cheesy ground from the factory.

[Glenn Moyer]

My Comanche does the same thing with the dash lights! Also my wipers have no umpf when the windshield is only parcially wet. Took apart the wiper transmision and cleaned an greased up all the joints, still not the way they should be. I was even going to change out the wiper motor. Can't wait to see if the ground is what's causing the problem. Thanks For The Tip !!

Glenn

[cruiser54]

Glenn, aside from just the instrument panel ground, the Renix Jeeps in particular suffered from an under-engineered electrical grounding system. Have you ever refreshed all your grounds like this?

 

Renix Ground Refreshing

 

The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.

 

The components grounding at the dipstick tube stud are:

 

Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.

 

The factory was aware of the issues with this ground point and addressed it by suggesting the following:

 

Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.

 

Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.

 

While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.

 

Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.

 

First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.

Remove the other end of the cable from the rear of the head using a 3’4” socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.

 

A suggestion regarding the braided cable:

I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18” long with a 3/8” lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.

 

A further improvement to the grounding system can be made using a #4 cable, about 10” long with 3/8” terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.

 

 

 

If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.

 

 

Revised 11-28-2011