Find a shop in your area that has an ASE master technician on staff and uses the ALLDATA information system, as well. The shop may be able to pinpoint the origin of this problem by using wiring diagrams and pinpoint values. The diagnostics will take less time if the problem is present.
One final thought would be to check the power control panel under the hood. Look for loose wiring at the panel, and also listen carefully for a buzzing relay. Water intrusion to the power control panel will cause the problems you mentioned.
Car Care Tip: According to state law, studded snow tires must be off vehicles by April 30.
Larry Rubenstein is a master technician who owns a North Shore service station. His column appears every Saturday. Write to Larry at The Salem News, c/o Auto Scanner, 32 Dunham Road, Beverly, MA 01915, or send an email to firstname.lastname@example.org.