I have a weird problem with my 03 Dodge.
Sometimes it seems to charge normally. Meter says it's making about 14.2 Volts.
Then, from time to time, it won't charge at all. After a few seconds to a few minutes of running, with the Volt Meter showing about 12.5 volts, the meter will swing to 8V, and the Check Gauges light will illuminate.
This has been going on for a week now. I had a load test run on both batteries and they are like new strong, so no problems there.
So, I bought a new alternator and installed it. No changes. Sometimes it charges, sometimes it don't, and the gauge goes to 8V and the chime/Check Gauges light comes on.


Any ideas?

 

battery wires?? But the first few minutes up to 5 mins of truck running your grid heater may cycle ... that depends on outside air temp though... Might want to unhook the grid heater and check it in the morning grid heater is on the intake horn its mounted under really.. You will just need to take the ground wire off.. see what the gauge does with it off.. If its still drops then hook it back up.. Seen and heard of a few drawing to much power causing the volts to drop low and the Alt can't apply power fast enough.. plus the Alt isn't going to charge because the temp sensor under the drivers side battery isn't telling the computer to charge yet.. so maybe the temp sensor under the battery is having a fault.. Since I don't work on Dodge trucks.. Our trucks don't have them so I can't tell you what they do or don't do if that sensor goes bad...

 

i thought about replacing the wires.. was going to do that tomorrow morning. I doubt it is a temp thing, It happens after it has been running for a while. so having the grid heater be the cause is doubtful. Also I live in AZ with 100+ temps ;-) i don't think anything needs pre-heated... lol...

 

I missed the AZ part Yeah pre-heated is not required in your state... I'm guessing with out testing your battery cables are loose or just trashed... I'd ohm them to see.. so much resistance per foot of cable and size of cable. You would have to google that one... but its probably the cross over cable from one battery to the other side..
Also did you have the batteries checked single or have them hooked together? I test them single. My thought is one will cover for the other if its tested together.. if they are disconnected from each other then I think you will get a better reading...

 

They were independantly tested. i took them out of the truck and brought them to Autozone. They are also less then 6 months old. I replaced them with my tax return check. Bran new Optima Blue's. I'm thinking it could be battery cables. That is why i'm replacing them tomorrow. But there is still doubt, so i'm trying to see if someone else knows of what it could be... ECM or somethign..

 

battery temp sensor under the drivers side battery is my guess...