Electrical: 5v at Booster Post, 12v at Battery
So im having starting issues again with the car. The battery is testing at 12v at the battery, but the booster pillar is testing at 5v. This happened before and it was the starter kill relay that had rusted and wasnt connecting the starter wire...this is not the case this time. I have an aftermarket alarm/starter installed, never had an issue before. This happened completely randomly.
car starts but only with a boost from the booster pillar, otherwise it sounds like a dead battery despite it being a few months old and testing at 12v.
Any suggestions to try out? So far I have removed the alarm and starter, and bypassed the starter kill relay to no avail.
Ive done car installs for 2 years professionally so I have a good understanding of car electronics. Also, the hood fuse box is testing at 5v (obviously since the booster post is the wire powering it)