I had a battery drain problem, used a test light to figure out which circuits were causing the drain, but haven’t been able to find much on line to figure out what to do. The three fuses I identified were ATC (transfer case) and TBC (truck body computer) in the engine compartment fuse block and RDO BATT (radio, battery) in the instrument panel fuse block. Any suggestions where to go next?
Current drain should be no more than around 80 milliamps while the car is parked. The computer and radio need power at all times to keep the memory alive in them so you may be sidetracked on those areas since they normally always draw current. The transfer case area may be the real cause of the trouble. I suggest you purchase a DVM to help you do this trouble shooting. Get one that can handle a 10 amp current test. You should be able to find one for under fifty dollars. Then you can actually measure how much current is being drawn. Investing in a good service manual is also money well spent. You may also be able to get some info on the wiring at your local library. By disconnecting connectors down stream of the light probe monitor you will be able to see when the current draw is stopped and confirm you are on the right track to the fault.
The maximum parasitic draw on this year/model that I used in diagnosis was 35milliamps,you are certainly free to select a value that you are comfortable with just my humble opinion.
You are correct about the current draw Oldschool. Your figure is really a more realistic average for most cars I think. I just use 80 mills as a high end figure in case some other extra accessories are installed.
BTW: After reading some of your previous posts in the past, it is pretty obvious that you know what is going on under the hood.
I had a similar problem. After 4 or 5 days the battery would die. After visiting the dealer the problem was found to be a relay in the lighting system (brake lights)that partially opened/closed. They changed part #: 12088567 with part #: 19115080.
The part costs about $20.00. The dealer charged me $475.00 to find the problem! I have contacted GM to see if the charges are correct and if they don’t have a better way of checking for that problem.
I hope I save someone some $$$.
A $30 electrical multimeter and these instructions: http://www.aa1car.com/library/battery_runs_down.htm
Just some info gained from working on plenty of these Blazers (my area was electrical,AC,light line,interior trim,accessories,alarms,keyless) there is a electrical cable group that powers the drivers front seat,this group likes to rub on the seat legs and short (inop power seat,windows,locks) it was very common.