So i took my jeep for a drive. It had lost power and died. I put new gas in it. Then got it jumped. Then i drove for 20 seconds and it died. So i figured ah alternator im sure. I picked up a new alternator today. Put in the battery jump started it. Then same problem. I put in a known good charged battery and bingo drove like a champ. I have no guages. I have dummy lights. But when i put the known good battery in it and drove there was no dimming of lights and the dummy voltage light did not turn on. I pulled it in to the garage. I kept it running and took the positive cable off and it died. All the connections to the alternator are good. The battery connections are good. So what would the problem be??!?!?!

 

First of all, never ever ever take the positive cable off the battery to test the alternator! That is an old school trick that while could be used many years ago before solid state electronics became standard, is dangerous to do now. I cannot tell you how many computers and alternators I have replaced over the years where people have tried this. Here is a link to an article that describes why this shouldn't be done.

http://www.troubleshooters.com/dont_...ct_battery.htm

Quick and dirty troubleshooting of the charging system can be done with a simple $10 multimeter. Put it on DC volts, put one lead on each of the battery terminals. With the vehicle running, you should be in the 13.5 to 14.0 volt range with a good battery/good charging system. Start there.

 

^This^ !!!

I have posted a writeup on a simple and safe (for your system - safety for you is up to you...) method to test your primary electrical using that $10 multimeter, a helper (it simplifies things,) and 20-30 minutes.

While not a quantitative test, it is a very good qualitative test. It's somewhere in the General Tech section (whatever it's called here,) and is a thread started by me. No, I don't have a link handy - search for "Battery", "Starter", and "Alternator" in any combination.

 

I replaced the alternator, battery, terminals, connections are ALL good. I turn my heater on and it dims my lights dim a little but i drove about 20 miles, and had all the lights on so i think it's okay. I'll get the volts tested soon but what do you guys think?! thats eerything in the charging system that you can replace.

 

Probably need to also check your grounds.

They seem to be barely adequate on a good day on our Jeeps.

 

Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

 

Wiggle the wiring harness while it's running with a vote meter hooked up.
Certainly sounds like a break somewhere.
I had the issue before and it turned out to be the connection at the firewall.