voltage regulator mod

I found mopar1973mans voltage regulator mod for older trucks, but no info on newer trucks. I am trying it anyway. ran separate 12v power from fuse box to old style regulator on firewall, disconnected alternator from harness ( brown wire was keyed voltage-8.5v?),. now I have a ck gages light and no voltmeter in the truck. voltage while truck is running = 14.75 to 15 v.
I will let you know how this plays out!

I wonder if a resistor in the rotor would fix the original over charging problem. Craig

Chrysler products alternators haven't had voltage regulaters scine the 1980's. the ECM turns the alt off and on, that's why your battery boils.your cross over cable has corrosion inside not just at the connections.you need to do a resistance check then you will see the problem.

you can do a voltage drop test as well... with the truck running put one end of digital volt meter on one positive post and the other probe on the other positive post... if you read a voltage other than zero, that is a voltage drop... you need to do this on both the positive and negative posts... remember your going from + to + and - to -.... than do the negatives to the chassis or alternator... if you read less than .1 volt your ok...

I also own an 05 and I personally think you might have one or two other problems.. 1 - a bad cell in a battery would cause it to gas off and boil the water 2 - a bad connection where the ECM see's the voltage would cause this... however I don't know where it reads the voltage... 3 - I'd just for the fun run a test from the frame of the alternator to the frame or ground on a battery looking for a voltage drop... 4 - this could any connection or a group of connections on the ground side..

I did the resistance check on that cable when I cleaned the connections.
.5 ohms. is that ok?
jelag, i will try the voltage drop test if this doesn't work. thanks

Check each battery separate while charging. The passenger is probably the one overcharged and boiling right?
As everyone has said. The crossover corrodes underneath the insulation right where it connects to the drivers battery.

Your keyed voltage at 8.5 volts is probably because that's what the drivers battery has. The passenger is overcharged. Even with a separate your duplicating the problem using the dead drivers battery as your sense lead to the regulator.

Wiggle the crossover while checking it. Also you will also notice it feels different than the other side due to corrosion.

Have you changed the batteries?

Subscribed... Good luck

I think it is under control now. although i do need to add a different voltmeter so I can see what the charge rate is all the time.
next comes new batteries, these might not make it through the winter!
thanks for listening!!

as mentioned above, cross over cable likely the problem, if you had .5volt, its too high that tells you the cable is bad

nickg said:

as mentioned above, cross over cable likely the problem, if you had .5volt, its too high that tells you the cable is bad

Click to expand...

.5 ohms not volts. is that too much resistance?

I thought you posted the voltage drop test so .5 V would bee too high

Here is a good link on how to do a starter drop test, its pretty easy
VWVortex.com - How to perform a voltage drop test

actually on that large cable (battery to battery) you should have a reading of O resistance, so I'd say the cable was bad

you might be able to used 2 volt meters one on each battery at the same time and see if one reads higher than the other, that would confirm a poor connection between the 2 batteries

nickg said:

actually on that large cable (battery to battery) you should have a reading of O resistance, so I'd say the cable was bad

Click to expand...

Not exactly. You're assuming perfect calibration of his multimeter, perfect connection with the meter leads and a perfect connection from each lead to the ends of the cable.

Regardless.... measuring the resistance for your cables won't prove much except there is continuity through the cable.

As an example I've had battery cables that read good continuity and voltage but wouldn't turn the starter. When I pulled the cable out and cut back the insulation.... 95% of the cable was corroded and the 5 remaining strands were fine.

black93gt said:

Not exactly. You're assuming perfect calibration of his multimeter, perfect connection with the meter leads and a perfect connection from each lead to the ends of the cable.

Regardless.... measuring the resistance for your cables won't prove much except there is continuity through the cable.

As an example I've had battery cables that read good continuity and voltage but wouldn't turn the starter. When I pulled the cable out and cut back the insulation.... 95% of the cable was corroded and the 5 remaining strands were fine.

Click to expand...

not sure if you are agreeing or arguing...sounds what what i said, his cable showed resistance, when it should not have any,(being a large cable) hence the voltage drop test to confirm resistance in the cabling, or cut it back and look for corrosion

nickg said:

not sure if you are agreeing or arguing...sounds what what i said, his cable showed resistance, when it should not have any,(being a large cable) hence the voltage drop test to confirm resistance in the cabling, or cut it back and look for corrosion

Click to expand...

Both agree and disagree. I agree that there shouldn't be resistance in the cable but half an ohm isn't exactly a smoking gun. That could be attributed to the meter, leads etc. He could have no resistance but a cable that's junk.

Using the voltage drop like you said is the way to go. You could even use jumper cables between both batteries to produce a verifiable difference.

Also don't forget the negative cable. Could be a possibility as well.

I will do the voltage drop test today, before I change the batteries. I really appreciate all your input!!

I didn't imagine you wouldn't have bought batteries.

Which battery was boiling?

If it was your passenger only back to crossover cable.
Just wiggle the wire or cut a half inch of insulation back right where it goes into the drivers positive battery lug. Then cover it with dielectric grease and tape if you find it's good.


If you do a voltage drop test do it between the two positive battery terminals not the starter lead.
Your starter wire is not causing an overcharge.

Other than bad battery connections and their grounds nothing can cause one battery to boil over and the other to be charging properly. Except for two dissimilar batteries. You should replace them asap if one is stronger. Charge them and have an ampacity and load test done by a truck shop or decent auto parts store that does both.

it started with the pass side but when I ran it with just d s battery, it boiled also.
I did not change batteries because i did not want to trash new ones before I fixed the real issue.

update on volt reg mod

there was no corrosion in either battery cable.
new batteries in dec 2013 - now july 14 and 13k later. regulator mod is keeping the batteries charged properly, but the lights still flicker. voltage @ pas side batt varies from 14.47 to 15.2 every couple of seconds. it seem to surge slightly @ idle also
I also have had some issues with the right rear bulbs - the reverse and the brake bulb plastic were partially melted, causing a 'lamp out' idiot light.
am I endangering the ecm?