Recently the battery light on my truck started coming on and staying on and checked the voltage while running and it is showing under 12V. I know that this means the alternator is not charging.

I had the alternator tested and I was told it is good. When it rains or if there is a lot of moisture in the air the light goes off until i put a load on in(i.e. headlamps, wipers,etc)

I found a section of the wiring harness that had made contact with the exhaust and I repaired the melted section.

I have no check engine light. I have checked fuses and none are blown. I have also inspected and cleaned every ground point i could find.

 

Most likely the GEM module is corroded or bad. Wet weather means problems for the GEM if it has corrosion or gets wet itself. It is behind the interior dash fuse panel. I'd certainly check that before going any further. This is a well known problem, especially when moisture is in the air.

Does your windshield leak water into the cab? Did you have the windshield replaced? If you have doubts, type in GEM in the forum's search box and see what I'm saying.

 

I have not had the windshield replaced or found evidence of it leaking.

 

You don't have to have evidence for it to be leaking. If you want to be 100% sure it's gem replace alternator. Trace down every wire

 

Do you think when the harness shorted against the exhaust it could have fried the GEM?

 

Haven't heard of it. But I do believe it's from gem not playing well with water.

 

I'm going to check it tomorrow morning. I didn't have any issues with charging until a few days ago. I thought the melted harness to be the culprit. Would the GEM cause the truck to not charge the battery?

 

If it is not leaking it is not Ford.

Check the voltage of the (+) wiring harness going to the alternator. Check the voltage of alternator (+) terminal and ground. Is it equal to battery voltage?

 

I'll have to recheck this when I get off work. I did check the + alt wire to the batt -. I believe it was the same.

 

While running the batt - to alt + cable reads the same as battery voltage. Alternator is NOT charging at all.