1997 Ram 1500, 5.9L

New alt and battery.

An alternator test done by Autozone sees 12v going into the batt, not the 13.5v they're expecting. We think there's a drain somewhere.

Possibly related issue: recently the "maint required" light came on. Checked and there's no error code. AC compressor and radio stopped working. No blown fuses.

My Question is: what could the "maint required" light mean, and could it be related to these issues?

 

Are all your connections to battery and alternator free of corrosion? Tight? Who replaced the alternator and what brand is it? It is possible you got a bum alternator.


Our 2nd Gen's are very battery/alternator dependent. More so than any other vehicle I have owned TBH.


Do you live near an ocean or salt lake? Check the important grounds too.


Some good soul posted the entire Mopar service manual for our trucks on this site. DL that and good luck.

 

This was a bench test, or an in-vehicle test? If on the bench, obviously enough, the alternator is trash. If in-vehicle, it's time to troubleshoot rather than guess.

The voltage regulation circuit is insanely simple: When the sensed voltage drops below the lower threshold the alternator goes hard on. When the sensed voltage rises above the upper threshold, the alternator goes hard off. If you're seeing battery voltage (12VDC) while the engine is running, chances are that the alternator's just along for the ride and doing nothing. Hang a clamp-on current clamp on its big output wire and see if there's appreciable current flowing toward the alternator (as during charge the current flows away from the positive terminal, opposite the direction of discharge). Report back your findings and I'll point you in the appropriate direction from there.

When, in relation to the initial failure, did the compressor and radio stop working?

 

These trucks are really sensitive to ground issues. Check all your grounds. Fixed more than one problem for me. If all those check out. Do what UnregisteredUser suggests. Hes a smart one

 

Much appreciated gents.
The connections are all clean and new, don't live near salt.

I put two brand new alternators in and tested them both within the same hour - and they both read the same, 12.xx volts. The tests were in-truck with engine running, not on the bench. So I feel chances that I got a bum alternator are slim.

I didn't know they were hard on/off - that could possibly explain it because the battery is brand new and fully charged.

Timeline:

"Maint Required" light, AC compressor and radio: they all triggered when my old battery "went dead." I replaced the battery, which went dead after a few days because it was presumably not getting charge. Replaced the alternator today.

I don't have a clamp tester - but I have a multi tester -can I do the
direction of flow" test using that?

 

See if you are getting higher than battery voltage out of the alternator, if you aren't, given that you have replaced it twice, chances are good the voltage regulator is toast... Unfortunately, that's part of the PCM, and is not user serviceable. You will have to replace the PCM.

 

Naaahhhhhh... it's less than a hundred bucks and an hour to rig up an external voltage regulator.

 

Nope. You can, though, do the initial testing detailed in section 8C of your factory service manual. It might show something. If it doesn't, you're feeling adventurous, and have got steady nerves and hands, try the following and if possible have a trusted helper working the ignition switch and controls inside the cab, ready to switch off the ignition quickly if you holler:

VERY positively identify the Field(-) terminal on the alternator. Refer to sections 8C and 8W in the factory service manual to make the ID, and if you're not absolutely certain that you've got it right just close the hood and walk away. Once you know where Field(-) is, get yourself a relatively healthy jumper (as opposed to some itty bitty 22 gauge thing), isolate one end so it cannot short to anything at all, and hang the other end of the jumper on the Field(-) terminal stud. The flying end of your jumper should be secured in a place where you can safely grab hold of it when the engine is running, as it will be soon. Put the voltmeter across the battery so you can monitor battery voltage.

CAUTION: IF YOU SEE >=14.0VDC ON THE VOLTMETER, QUICKLY REMOVE THE JUMPER!

Start the engine, crank the heater blower up to max, turn on the headlights, and switch them to high beam. If the alternator's loafing you'll see battery voltage or a low battery voltage on your voltmeter, the headlights will be dimmer than normal, and you're ready to go. If you see normal charging voltage you've just seen some magic, and should abort the test by shutting down the engine and tearing down the test setup.

Now: Keeping in mind that as long as that ground is applied, a functional alternator is going to be hard on and if you create a gross overvoltage you're surely going to let all kinds of magic smoke out of expensive parts. Ground that flying end of the jumper, and look at the voltmeter. If the voltage is not increasing, slowly increase the engine speed to either around 2000RPM or until you see a voltage increase, whichever comes first. If you don't see a voltage increase within a few seconds of reaching 2000RPM, call it quits. Kill the engine, then turn off the headlights and heater blower.

If you saw a voltage increase, visually and electrically inspect all of the conductors and connectors on the alternator and their terminal points far away at the PDC and PCM. You're looking for shorts, opens, and/or excessive resistance. If you test all of them and find no problems, then you're probably going to want to install an external voltage regulator -- just search the web for the instructions and parts lists, as it's a common enough thing to do and is documented all over the place. You could replace the entire PCM, but if all that's failed is the field winding driver you're spending hundreds of dollars to get a three dollar part. The external regulator setup will run you in the neighborhood of thirty to fifty bucks or so.

If you didn't see a voltage increase, either you're not getting your Field(+) source or the alternator is hosed. The factory service manual can help you to find out about Field(+), your well equipped friendly local auto parts store can bench test the alternator.

Don't buy things like alternators from any of the big discount chains like the one you got the current one from. They're quite often DOA, and don't last fer 5h17 when they're not DOA. My personal best on similar parts was three DOA's in a row of generators for a '72 VW Beetle. I wasn't the one selecting the parts -- the fourth one came from the NAPA I would have gone to in the first place and AFAIK was still in place when she sold the car several years later.

 

Did you happen to check the large (120 amp i believe it is) fuse in the engine compartment?

 

Thanks for the tips and advice gentlemen!

The other day I looked up and did a bunch of tests with my multimeter - confirmed I was getting no charge. So I took it to the local shop and they replaced the "alternator fuse" which I honestly never heard of. It's working now! $7 part, $80 charge... You were right on the money Moparite.

Still no radio and AC, but fuses look good... Going to hunt that issue down now. I'm assuming there's a way to test the AC clutch relay?