I have a 2005 gmc sierra thats had intermittent electrical issues for 2 years now. It usually only happens in the winter time. The door locks, windows, mirrors, blower motor, interior and dash lights and temp display on the rearview mirror go out sometimes on their own or when i step on the brake pedal. If i tap on the dash pad near the center most of the time all of these concerns correct themselves. Ive noticed too that every now and then the SERVICE BRAKE SYSTEM & SERVICE 4WD messages do come on in the DIC, ive cleaned the ground on the driver side frame rail and checked both grounds at the a-pillars. Fuses also seem ok and not sure where to go from here.

sometimes the fuse sockets are loose, so it maybe good but still only flow power intermittently. also possibly a ground under the dash somewhere, if there is one

Ive checked the fuses and terminal tension of each of them. But the weird thing is when i step on the brake pedal most of the time it shuts off the blower motor and the dash lights/ Any ideas??

it has to be taking the current capability from the other things that shut off, it has to be a poor connection in either the +12 feed or ground. some times if you check the fuses and ground with a meter with stuff on it will show weird voltages like 5 to 9v on a fuse or any voltage referenced to battery neg on a ground means its bad

How do i check fuses with a meter?

Park your black lead on battery neg. Then the fuses normally have external slots to measure the volts. Measure both sides and see if wiggling changes the reading

The ignition switches are pretty common issue on these trucks not sending enough voltage out.

Ive changed the ignition switch 3 times the first time i changed it was to try and correct this problem. After that i had to change it twice to correct a no start on my truck. Im thinking that maybe the orange ignition wire that goes from the I/P fuse block to the ignition switch may be shorted or have a poor connection at the fuse block.

Any ideas?

Have also seen poor terminal tension and internal shorts in the fuse block. Best way to check is pull the fuse block out and check all your connections on the back.