The firewall to frame ground 4x4 was talking about. See auto-merged double post #6.

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I'm not positive, but I'm pretty sure my Genos harness is grounded on the battery.

 

Typically a big ground like that is used to transfer higher current loads such as starter current that "builds" up. The headlight system would typically be checked via the ground it used. If that ground indicated high voltage while cranking along with other grounds it could be a culprit but very rarely is a condition like this be seen. These trucks are so ground sensitive that other issues usually accompany or proceed a issue like yours. In about 4 of 5 cases you'll see a dim headlight with a faulty ground.
If a body ground or block ground were to be the cause of your issue it would likely result in high voltage at the ground circuit while starting the truck. If I had seen repeated bulb failures in multiple locations I might consider a broader scheme than moisture or vibration and look into a possible failed or open alternator diode.
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Oh, that's another thing, I just replaced the alternator too. Not because of this, but this has been going on for months and the alternator was just a week or two ago. Regardless, I guess I need to get out my voltage meter and start poking around. I'm getting a new plow soon, which will be preceded by ripping all the old plow electronics out, should be a good time to get at it all.

 

Reading over my message I forgot to mention. You must check your ground circuit with the lights on and connected.

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OK, thanks.

 

Still haven't had time to look at this, but I plan on installing a new plow Friday and will be ripping all the old plow wiring out. Should be a good time to troubleshoot this, with the eminently qualified tech who will be there.
In other news, the high beam that was out last time I posted here is working again.

 

oh yeah ... didn't know you had plow and lights ... ... that would be a good start to look through that wiring