1976 d100 overcharging
04-24-2016, 12:02 PM
#1
1976 d100 overcharging
my truck has had this issue for a while and im very puzzled. I have good ground to VR, it has a good ground to the firewall and i have a ground wire running to the head. The green alt field wire only shows 1 volt when running, while the other one shows about two volts under what the battery and alternator are. Sometimes it stays around 14 volts at idle, sometimes 15 after i give it throttle, it goes no higher than 16 volts.
I looked at a diagram online, it showed the green alt wire going to the bottom left place on the VR plug, and the red alt wire going to the top part of the VR plug and to the ign switch. Well The green wire is right, but from the red alt wire, it goes to a welded splice which sits right in front of the ballast. Also the red wire from the VR plug goes to that splice also. So i didnt know if thats right. Also connected to the splice is the two wires coming from the top plug on the ballast, a wire from the ign control module, a wire that runs to the ign switch, also i added a wire from an electric fan and electric fuel pump. what is wrong? sorry for the long text
I looked at a diagram online, it showed the green alt wire going to the bottom left place on the VR plug, and the red alt wire going to the top part of the VR plug and to the ign switch. Well The green wire is right, but from the red alt wire, it goes to a welded splice which sits right in front of the ballast. Also the red wire from the VR plug goes to that splice also. So i didnt know if thats right. Also connected to the splice is the two wires coming from the top plug on the ballast, a wire from the ign control module, a wire that runs to the ign switch, also i added a wire from an electric fan and electric fuel pump. what is wrong? sorry for the long text
04-25-2016, 09:15 AM
#3
This is a popular problem with Mopars, specially the older ones.
The trouble is from most likely to least
1..Voltage drop in the hot side of the harness, probably the most common
2..Voltage drop in the ground. Don't just LOOK at it, you can test it, see below
3...VR not properly regulating. Fairly rare. Most of these either work or don't
4...Battery. Rare but can happen. Easiest way is to swap in a known good battery and see if it straightens out
To test this........
1....Hot side of harness. Obtain a way to get to the VR IGN terminal, which is difficult. The same electrical "point" comes off IGN1 and feeds the VR, the ign ballast, the alternator blue field, electric choke if used, and some smog doo dads on some years and models.
So Turn the key to "run" with engine stopped and probe the ballast resistor connections for the highest reading. This is your IGN run line.
Two ways to check this.....
A.....
1...Carefully, accurately measure voltage from ballast to battery NEG post
2...Carefully measure battery voltage directly at battery posts, and then subtract the two readings
B....Second method is to read directly. Once you have found the high voltage point on the ballast, leave one meter probe at that connection. Remove the ground probe and stab it right into the battery "hot" post." Set your meter for low DC volts. What you are hoping is a VERY low reading, the lower the better. More than .2--.3V (3/10 of one volt) indicates a problem. Any reading here is ADDED to the VR set point. This means, EG, if the VR is properly regulating at about 14, and you have .8V drop, then the battery will charge at 14.8
CHECKING THE GROUND
Get engine warm (VR is temp regulated) and battery "normalized." Run this check first with all accessories off, and again with heater, lights, etc, turned on.
With engine running at a med. RPM to simulate "low to med" cruise speed, Stab one meter probe directly onto the VR mounting flange. Not the firewall, the VR flange. Stab through any chrome, paint, rust.
Stab the other probe into the top of the NEG battery post. As the first test, you are hoping for a very very low reading, the lower the better. More than about .2V (2/10 of one volt) means check further. You MUST have a good ground path from VR to battery.
HOW this happens.
Ground is fairly obvious......Not enough grounds, not large enough, rusted, corroded connections.
The hot side, on older vehicles, depends a bit on the model. But the voltage drop is "anywhere" in the path from battery to VR that there is a connection. On older veh. this includes the BULKHEAD CONNECTOR, THE AMMETER, IGNITION SWITCH CONNECTOR, IGNITION SWITCH ITSELF, BACK THROUGH the BULKHEAD CONNECTOR
And do not forget the VR CONNECTOR ITSELF. Remove it, examine, and "work" in and out several times to scrub the terminals, and to "feel" for tightness
and of course any problems with splices and connections, hacks, etc along the way. Some newer models had an engine harness disconnect, separate from the bulkhead connector. That damn thing was a poor design and probably should be hard spliced and eliminated
The trouble is from most likely to least
1..Voltage drop in the hot side of the harness, probably the most common
2..Voltage drop in the ground. Don't just LOOK at it, you can test it, see below
3...VR not properly regulating. Fairly rare. Most of these either work or don't
4...Battery. Rare but can happen. Easiest way is to swap in a known good battery and see if it straightens out
To test this........
1....Hot side of harness. Obtain a way to get to the VR IGN terminal, which is difficult. The same electrical "point" comes off IGN1 and feeds the VR, the ign ballast, the alternator blue field, electric choke if used, and some smog doo dads on some years and models.
So Turn the key to "run" with engine stopped and probe the ballast resistor connections for the highest reading. This is your IGN run line.
Two ways to check this.....
A.....
1...Carefully, accurately measure voltage from ballast to battery NEG post
2...Carefully measure battery voltage directly at battery posts, and then subtract the two readings
B....Second method is to read directly. Once you have found the high voltage point on the ballast, leave one meter probe at that connection. Remove the ground probe and stab it right into the battery "hot" post." Set your meter for low DC volts. What you are hoping is a VERY low reading, the lower the better. More than .2--.3V (3/10 of one volt) indicates a problem. Any reading here is ADDED to the VR set point. This means, EG, if the VR is properly regulating at about 14, and you have .8V drop, then the battery will charge at 14.8
CHECKING THE GROUND
Get engine warm (VR is temp regulated) and battery "normalized." Run this check first with all accessories off, and again with heater, lights, etc, turned on.
With engine running at a med. RPM to simulate "low to med" cruise speed, Stab one meter probe directly onto the VR mounting flange. Not the firewall, the VR flange. Stab through any chrome, paint, rust.
Stab the other probe into the top of the NEG battery post. As the first test, you are hoping for a very very low reading, the lower the better. More than about .2V (2/10 of one volt) means check further. You MUST have a good ground path from VR to battery.
HOW this happens.
Ground is fairly obvious......Not enough grounds, not large enough, rusted, corroded connections.
The hot side, on older vehicles, depends a bit on the model. But the voltage drop is "anywhere" in the path from battery to VR that there is a connection. On older veh. this includes the BULKHEAD CONNECTOR, THE AMMETER, IGNITION SWITCH CONNECTOR, IGNITION SWITCH ITSELF, BACK THROUGH the BULKHEAD CONNECTOR
And do not forget the VR CONNECTOR ITSELF. Remove it, examine, and "work" in and out several times to scrub the terminals, and to "feel" for tightness
and of course any problems with splices and connections, hacks, etc along the way. Some newer models had an engine harness disconnect, separate from the bulkhead connector. That damn thing was a poor design and probably should be hard spliced and eliminated
Last edited by DDodger; 04-25-2016 at 09:21 AM.
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