I have a 91 Dodge 1/2 ton truck with 100+ K miles (exact mileage for another thread due to speedometer not working) with a 318 engine. This is a work truck used for a side business that’s not used daily.
Recently the battery has been dying and was replaced in Oct. because it failed the load test. Battery kept dischrging so I checked the voltage at the battrey and had less than 12 volts. I pulled off the alternator and it tested fine on the bench test. Chilton book is no help with this so where could my problem be?
You have a bad voltage regulator. This truck probably has the voltage regulated by the ECM, and that circuit is burned out. I had successfully put an older style transistorized voltage regulator on a Dodge Caravan for a friend some years ago.
This meant cutting the green wire, which is the field control, and splicing the blue wire, which is the 12V reference, and hooking them to the voltage regulator. Keep as much as the green and blue wires from the alternator as possible, since these are fusible wires as a safety feature.
Connect the green wire and the blue wire to the voltage regulator with a butt connector if you cannot find a pigtail.
Check the voltage at the battery after the engine has run a few minutes and with the engine off. Post back here.
I put the charger on it overnight and am getting ready to put it all back together. I checked autozone and Advance for price and availability for another ECM and am looking at about $200.00 and both have to special order. I like the bypass idea and what kind of regulator should I ask for at the parts house?
I asked for a voltage regulator for an '87 Dodge van, and they had the electronic one in stock (first picture). The pigtail I couldn’t find, and just used female bullet connectors. I suppose a pigtail could be found at a junkyard. Be sure to pay attention to the green and blue connections on the wiring diagram. That’s very important. Also, find a good flat location and use sheet metal screws for good grounding. This is also important.
Thanks. I looked it up and it seems like all models use the same one. $43.00 is easier to handle vs. the $200.00. I’ll go to the local u-pull it and get a pig-tail. Do you think a voltage regulator from the recycle yard would be ok to use?
Maybe, but I’d sooner replace it with new. Just me, but I don’t like using electrical parts from a junkyard unless I have to. Too high a risk of failure.
I’m thinking the same way about used electrical parts. Sure I could get one and it would work fine but with my luck, it would malfunction sooner than later. Thank you for your help with this issue. I will be going tomorrow AM to the u-pull it and get a pig-tail then pick up a new regulator on the way back.
I posted here several months ago about a neighbors Chrysler car which was not charging.
It turned out to be the 12v. from battery to alternator was not making it because the cable connections were bad. He wiggled things and it worked for a few days, then went away again. Sooner or later he has to replace something in that harness.
And, yes, that car, which I think was 91 or 92 also used the ECM for regulator.
As I mentioned before, the wires to the battery terminal and field windings are fusible wire. If those wires were overloaded once, or overheated, they are probably broken and unreliable. A simple ohmmeter test will confirm this. If they are burnt, they must be replaced.
All the fusible links tested good. I pulled the alternator off again and took it to get tested. Alternator was putting out 10 volts so went ahead and got a new one from Advance. I had them put the new one on the test bench just to verify it’s good…Putting out a little over 14 volts. Installed new alternator but it’s still not charging the battery. Ran to the u-pull and got a regulator and a pig-tail. Can’t install today but will update when completed.
UPDATE…Just got thru installing the external regulator as was suggested by BustedKnuckles and I’m getting 15 volts at the battery. Thank you for your help. I’m on the road again…Thanks again.