2000 Blazer 4wd Electrical Problem

I keep blowing the 4wd fuse (#15 in the i/p block) when I start my Blazer. It affects the fuel gauge, digital gear indicator and the battery light comes on. If I turn the key to Run before cranking, the fuse holds but as soon as I crank and start, it blows.

Anyone have any ideas?

This is a rather obscure problem due to the fact that the shift indicator light, fuel gauge and battery light do not have current supplied to them in the "start" position. Current is supplied in the "run" and "accessory" positions but it is interrupted in the "start" position. The reason the accessory circuits are interrupted is so the battery can supply full current to the starter, without any unnecessary draw. There is one place where all of these circuits are in close proximity to each other, the ignition switch. There are several contacts (circuits) within the ignition switch; therefore it is entirely possible for other accessories to be interrupted as designed, such as the windshield wipers, radio and heater blower, and yet have one or more other circuits malfunction.

If I am understanding you, you are suggesting that ignition switch may be defective. Your explanation makes alot sense. At the risk of rambling on, I'll give a little background on the problem. My work vehicle is a Colorado with an electronic ignition. Once the start position is engaged, the key can be released and the engine will crank on its own. I got used to that and turned the key in my Blazer to start and quickly let go before the engine started. That was the moment when the problems started.

I just got my hands on a full set of wiring diagrams so I'll start with the ignition circuit. Thanks for the help.

Looks like it was the transfer case switch ass'y. Go figure, thanks for the help. Now onto the door hinge pins. Lots of info that one here...

Glad to hear you've got it handled. BTW do you still have those wiring diagrams available? If so I would be interested in looking at them. PM me and let me know.