2003 Sierra electrical issue.

[Matthew Berggren]

Over the past weekend I acquired my late grandfather's 2003 sierra with the 5.3l. This truck only has 44,000 miles on it and ever since his passing in has sat around and now has has a pretty bad electrical issue. Everything I want to start the truck I have to jump it because the battery gets completely drained. Once it's running after being jump the instrument cluster takes about 5 mins to turn on. I've hooked a computer up to the obd and the pcm is giving out all the information but the cluster is getting power. I'm have a feeling that it's the bcm not going to sleep or is faulty and is draining the battery. If anyone has any insight or has had similar issues let me know.

[64BAwagon]

If the truck has sat for a while my first test would be if the battery is any good, the cables are intact and the charging system is working. I would also look in the underhood electrical box to see if there may be rodent damage to the wiring. I always start with the easy/cheap stuff first.