morgan320i

so my alternator seems to fluxuate , i replaced all the wires to the alternator and starter with 4 guage, it stays around 14 volts if im driving around town with the lights off, it drops to 10 or 11 volts if i turn lights on or when i turn my auxilury fans on, bad alternator?

freegdr

Have it check at the battery they say renix gauges are known to give false readings

Gee oh Dee

Is it just the gauge that shows low or do they lights actually dim?

morgan320i

so when i tested the volts tonight 12.6 car off, 13.8 to 14 with it runing and 13.7 or so with the 3 aux fans on and the lights on, but guage reads low like 9 to 13 amps

pickles

My volt meter does the same (even though voltage is fine).

5-90

Voltage and current are mathematically related in a closed electrical system, which a vehicle can be considered (yes, I know, it has a generator, and the generator is powered by the engine. But, the generator has a finite capacity, as does the battery.) cf: Ohm's Law, Watt's Law.

Therefore, IAW Ohm's Law, if current draw goes up then voltage must come down.

Hence, if you have a high-draw accessory turned on (auxiliary electric cooling fan, HVAC blower fan,) then you'll note a voltage drop and your lamps will dim. Sometimes, depending on what draws are already present in the system, you may even hear your HVAC blower slow down a bit.

Yes, this means your voltmeter will drop as well.

However, this does nothing to ensure the quantitative accuracy of the voltmeter - particularly on RENIX. I've long since stopped using mine as an absolute reading - I verify system voltage semi-annually with my good DMM (the Fluke I don't carry around, because I paid $800 for it 'way back when...) and move the grease pencil marking I've made on the gage window if I need to.

ANY suspect reading noted at the IP should be verified INDEPENDENTLY of the IP, with a known good meter or gage! - before ANY further troubleshooting action is taken. Consider this to be set in stone, for ALL vehicles. Even on OBD-II, I've run across "faults" where it was the gage that was wrong, not what it was monitoring.

cruiser54

Even after upgrading my cables on 3 Jeeps, I noticed the gauge read lower than the observed reading at the battery.

I read about this somewhere so tried it. It helped the gauge to read a bit higher.

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