Originally Posted by Tewksburyduck
Furnace, lights, and water pump work while on battery power only.
It does not take much reverse current to fry a computer. Sounds like it could be damaged. Did you check both fuses in the radio? There is one that supplies "full time" power (clock, panel lights, etc) and one that supplies "part time" power (all the rest - like DVD player).
The full time power is an inline fuse and the part time power is a "blade type" in the back of the radio.
You may need to meter them for continuity since they can fail at the solder joint and the open may not be visible.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW