Thank you npccpartsman for the link. I have been out of town working again and not checked this thread on a few weeks. I will get the part and make an attempt to repair it.

In further diagnosing the issue this morning I pulled the batteries and alternator and had them tested. Last night I drove the 80 miles home from the airport after the truck sat for 9 days in the airport parking lot. The battery light was on the whole way home. Also ecu voltage was 13.8 the whole way it never dropped below that.

I did not charge the batteries before load testing as I wanted to see how they would do after driving 1:45 with the lights on and the battery light on.

Battery 1: 850 cca Interstate
Voltage 12.64 Measured cca 797

Battery 2: 850 cca Interstate
Voltage 12.64 Measured cca 770

Both seem fine to me based on those results.

Alternator passed all the internal circuitry tests and excitation test. Output voltage measured 14.3 volts.

So armed with this info I am pretty certain it is a deeper issue than just the alternator or batteries.

Does anyone have experience working on the charging system wiring harness and/or instrument cluster. Particularly how they interface with each other. Seems I am going to have to go the hard route. Links to the wiring schematics would be especially beneficial.

Thanks again for all the input you guys have provided. I do appreciate it.

 

There is some info in another link titled "2006 F350 6.0 4X4 crewcab VOLTAGE PROBLEM" if you haven't noticed that one.