Electrical Draw Issues

ajmorell · 06-15-2012, 07:55 AM

Need some help with at least a starting point on diagnosing some weird electrical draw issues. Basically when any load is put on the electrical system the engine RPM's drop (at idle) and the lights dim (interior and exterior). If the radio is on, it shuts off. Initially I thought it was the battery but I swapped it with the one from my car just to diagnose and it still does it. It seems that it's only electrical stuff that's run through the PCM. I have lights hooked up directly to the battery (through a switch & relay) that do not draw down when a load is put on the system, nor do they affect the dimming/load I referred to earlier if left on. Voltage across the battery terminals at idle is ~13.4 Volts even with all of my lights on and the radio on, which seems normal. The voltage gauge on the dash does fluctuate quite a a bit (from 13 volts down to 10 or so when a load is put on the system) even though that's not reflected at the battery. I've checked all of the obvious stuff (power & grounds, fuses, etc.).

I need to do some more testing at the PCM to see if the voltage fluctuation is showing up there or not, but I'm wondering if anyone else has any ideas or at least obvious things that should be checked. I don't think it's the alternator since the battery holds a charge well even with a heavy draw on the system, but I haven't pulled it to get it tested either.

Thanks in advance

ajmorell · 06-15-2012, 03:31 PM

Bueller?

jtackerman28 · 06-15-2012, 04:15 PM

Either the alternator or the voltage regulator.

ajmorell · 06-15-2012, 04:50 PM

Then why does it keep the battery charged?

gactech · 06-15-2012, 06:26 PM

The alt may give you ample voltage but may not be able to give you the amps required to give the battery muscle. You can show 13 volts charging but only have half the amps required.

ajmorell · 06-15-2012, 09:07 PM

Unless the alternator was completely shot wouldn't the voyage fluctuate with RPMs? As of right now it doesn't, engine speed seems to be unrelated

gactech · 06-15-2012, 10:15 PM

It may be time for a rebuild. Pull it and take it to autozone. They will load check it

ajmorell · 06-16-2012, 08:06 AM

Thanks, I'll get it checked asap

**gunner44** · 06-16-2012, 04:04 PM

my thinking
If the alternator takes the load test. Remove the lights you added to the battery. When you start the jeep, (with everything off you have control of, this includes doors closed, A/C not in auto and system switches in off.) the starter sounded good? Engine runs good after starting without any driving problems? When you use the break no rpm drop?

If answers are yes, Turn on each system alone.
If the answers are No, It is in one of the major systems, starting, charging, Fuel/ignition.

ajmorell · 06-16-2012, 06:34 PM

Alternator checked ok. Starts, rune and drives fine except radio turns off and lights dim when load is put on system

**gunner44** · 06-17-2012, 08:06 AM

You'll have to turn things off and then turn them on one at a time until you find what system has the problem. If there is more them one there will be a common thread, it may be grounding or whatever.

"Starts, rune and drives fine except radio turns off and lights dim when load is put on system" This is the same thing you indicated above, confusing, -lights and radio are loads on the system, what other load are you talking about?

ajmorell · 06-17-2012, 11:24 AM

I should've clarified. When a heavy load is put on the system such as if I have headlights on, radio on, and I hit the horn or roll down the windows. The combination of said loads does not matter, which is why I do not believe the problem is with one of the specific systems but with the global system. I am leaning towards voltage regulator but since it's part of the PCM it's not exactly easy to diagnose

jtackerman28 · 06-17-2012, 11:59 AM

You can set up a external one.

ajmorell · 06-17-2012, 12:07 PM

Quote:

Originally Posted by jtackerman28

You can set up a external one.

Any idea where to find info on that?

**gunner44** · 06-17-2012, 09:28 PM

If it were me I would exhaust all potabilities before condemning the PCU. It is my opinion that Jeep would not be running down the street if the regulator was out. I would be eliminating the possibility of a short.

Then I would have a full test on the alternator. There are tests I would have made, if not comfortable by myself or not having the right testing equipment , by someone else. I would go to Fluke.com, sign in, go to “Beat the Book”, download it. Go to, and copy the alternator checks, take them with you and tell who you are dealing with you want them made. If his flinch I would walk out. The tests will determine if it is the alternator or the regulator if there is a problem. Note the alternator is loaded for its rated amperage, mine is 136 amps.