98 Silverado K2500 dash light dead short
 

Hey guys, I am new to this forum but you guys have answers to questions I didn't even know I had, so maybe you can help.
I installed a snowplow last winter. This truck was the "camper special" version with two batteries connected by a knife switch on the firewall, so I run the plow completely off the alternate battery. For the headlights, I decided to bypass the truck's wiring completely and instead power from the positive post on the underhood fuze panel. I have two switches that control the hi and lo beams of the lights which are lighted when switched on. For the parking and turn signals, I "T" tapped into the existing wiring on the drivers side fender wall. The plow is an older Western ProPlow cable driven plow, so there is no harness or ECU for the plow. Only power to a solenoid (battery direct) to engage the motor on the pump.
About a week after install with almost daily operation, the HVAC fan stopped working on speeds 1-4 but worked on 5 so I thought blower motor resistor right but didn't have time to change it so I ran with the fan on hi until the dash started smoking and the fuse blew for the dash lights. I traced the hotspot to the wiring harness that plugs into the actual switch and after a new wiring harness and switch (not the resistor), all fan speeds work again, but the fuse still blows. I have tried a new switch, and systematically unplugging, the gauge cluster, HVAC control, bed light switch, radio, CD player, ashtray, and even the 4x4 switch (even though those lights still work). Likewise, I have disconnected all components of the plow. After disconnecting each component, I replaced the fuse and subsequently popped it. :confused:
Any ideas, I am really scratching my head here and think the Buss company is about to name the new wing in their plant after me. ;)
Sorry so lenghly, I have tried alot!
Maybe worth mentioning, the first time I replaced the fuse, I only had a 30A. When I switched on, it fizzled and blew taking out the headlight and parking light fuses also.