ok so I just bought this truck and the guy told me the check engine light was on due to the external voltage regulator that he put on the truck. for the 1500 i paid for it i wasnt that worried about it. so anyways on the way home i notice that the truck is chargeing at around 16.5-17v. so i open the hood and he had wired an external regulator using the old wiring harness-a green wire and i forget what other color. so i buy a new regulator and install it according to the schematic that is on every cummins website. i start my truck and now it isnt charging. so i rechecked everything and i have ground on the voltage regulator and at the alt. i have keyed power to the top post which then goes to the alt. the other post on the regulator i have going to the other small prong on the alt. i removed the black box that was on the back of the alt which was originally attached to where the voltage regulator wires are now going, and added the ground wire to where the ground wire from the black box was attached to the alt. was i not supposed to remove this? there are no pictures of one of these setups that i could find with the mopar style regulator. and i know the alt is good cause hooked up the other way it was overcharging. any help on what i should check next would be greatly appreciated

 

I looked at the back of my alternator there is a terminal on the outside of the alternator and has a large wire connected to it going to the engine ground. There is another large wire hooked to a terminal on the back of the alternator this wire goes to the battery. There are two small terminals on the back of the alternator and these are the field terminals. They will have two wires that run up to your new voltage regulator nothing else should be connected to these two small terminals. At the voltage regulator if it is mounted with the connection point on the bottom the center wire is the power wire from the ignition switch. It does not matter which of the two wires are connected to which of the two terminals on the voltage regulator.

After installation turn the ignition on and check for power at the center terminal of the voltage regulator and at one of the small terminals of the alternator. I believe the other small terminal ( for my aging memory) should be at zero or very close to zero volts. The large wire hooked to the back of the alternator should also show 12 V. If by chance it doesn't check your wiring back to the battery. Hope this helps. Mike

 

well i have 12v at the terminal on the regulator and 12v at the alt. with the key on i didnt check the other terminal without the truck running. i know with it running i have 12v there as well. i thought that it might be a ground issue so i ran a ground wire from the battery to both the regulator and to the alt. i have ohmed out the wires that i installed to make sure that they were making a good connection. i guess the next step is to take the regulator back and trade it in for another one...the one i bought has a lifetime warranty on it--which is why i paid the extra money for it. as simple as this setup is i dont understand why it is that im having such an issue......any other ideas from members that have had a similar issue? im almost ready to just go and buy the ecm and replace it so i dont have to go through all of this bs

 

From what you describe the voltage regulator is at fault assuming it has a good ground. The way it works it applies 12 V to the field terminal through the field and back to regular where it controls the current flow for the field to ground. That is why ground is so important. Mike

 

Was the 16-17V measured with a reliable meter or is this what was showing on the somewhat sometimes inaccurate dash cluster gauge?

The EASIEST method that I found is when wiring in a voltage regulator to the alternator is forget about the confusing color codes. Buy the plug and wire it with one lead to each of the rear terminals of the alternator. Also add a third grounding lead connecting the alternator directly to the regulator mounting screw. Use an internal or external tooth lockwasher at this mounting point connection with a dab of grease on the screw and washer. Then find out which wire in the harness is the switched lead from the ignition switch. Probe both leads with the original harness disconnected. Make sure that lead goes to the rear of the alternator. The other lead remains disconnected. Attach the switched lead to the voltage regulator as indicated in the picture below to the switched lead. I'm told that you can connect a 50 ohm 1 watt resistor from the unused disconnected lead to the switched lead in the harness which should turn off the check engine light in the 92 & 93 trucks. I haven't tried that yet but it makes sense since the rotor in these alternators is above ground and there is normally a resistance measured across the terminals leads telling the computer the alternator is there and ready.

Voltage regulator plug connections:

 

ok well today i went out and checked with the key on engine off and the vr has 12.6v coming into it and i unpluged the other terminal off of it and it has 12.6v there as well. so im guessing that the vr is at fault??? which would really p!$$ me off that ive gone through all of this to get a bad regulator out of the box. and i didnt go off of the original wires--i ran new ones so that i didnt have to worry about if one of them was cut or grounded out somewhere. also am i reading it right that even after i get this alt charging correctly that there is still going to be a check engine light on?

 

so i put the original one back on and the alt is charging and fluctuating between 15.2v and 15v. i know that on a normal system you want between 13.5-14.5v...is this normal when you put the external vr on that it charges this high? and what voltage do i have to worry about it blowing my battery up?

 

The ABSOLUTE BIGGEST problem with these rigs overcharging is resistance in the firewall plug. EVERY Mopar I own has had this problem fixed by drilling through that plug and hardwiring that circuit. Now. My truck did this to me in Resume speed Nevada and I needed a quick fix. I put a relay next to the regulator feeding battery votage directly to the regulator with key on, OMG! The most rock steady voltage from Idle on up I have ever seen. I know its just one more part to fail, but I swear by it.

 

sorry it took so long...but i work nights and its been kinda hectic with the weather.. so i finally got a chance to take the "new" voltage regulator back and exchange it with another one. when i put it on i also ran it through a relay similar to the post above this one. it is charging properly and it is not fluctuating the voltage like it was before either....just dead on supply of power. now i just have to figure out a way to get the check engine light off for the alt codes and ill be good.

 

Maybe try what I suggested with the resistor above in post# 5 above?