1997 K1500 CTSY Fuse 3 Parasitic Drain

I have a parasitic drain on my battery. 4.5 amps to be exact. I've tracked it down to the CTSY fuse or Fuse 3 in the fuse block. When I pull the fuse it drops to 40 mA which is pretty normal. I've got diagrams that show this fuse powers quite a few interior lights. What is the most likely cause of this drain since my lights seems to be working and shut off when the doors are shut? I've almost got the dash rippped apart to get at the wiring harness but hopefully I can find it before taking the whole dash out. Any ideas fellas? Thanks in advance.

When you checked that fuse for drain did you wait any length of time before measuring? Some systems have to "sleep" then you measure drain.

Yeah..I did do that. Also since I'm able to let the truck sit I had the negative cable off the battery for two nights now and I check for the drain before I start to work on it again. Since everything is working I'm thinking its got to be short somewhere in that hot leg since that fuse is hot all the time. If it were shorted bad I would think the fuse would blow right away.

I wouldn't suspect a "short". A good wiring diagram and see exactly what is on that #3 fuse. Sometimes the manual or diagram on the fuse panel doesn't give the whole story. And then unfortunately process of elimination.

Yeah...I figured I was in the relm of just elminating legs of the circuit. I was hoping for an easy smoking gun. Problem is the harness is behind the dash, so that's my next fun task and then I can trace the connectors on it to isolate where the drain is coming from. I'll post again if I find it over the weekend. Thanks.

Yeah...I figured I was in the relm of just elminating legs of the circuit. I was hoping for an easy smoking gun. Problem is the harness is behind the dash, so that's my next fun task and then I can trace the connectors on it to isolate where the drain is coming from. I'll post again if I find it over the weekend. Thanks.

Do you have power door locks? Sometimes these can get stuck and cause the drain. Could also be your radio. Did you check ALL lights including the footwell lights and the glove box light?

So the problem turned out to be the Interior Lamp Control Module. Needless to say I slammed a beer hard after finding the damn thing. Since this was my first brain surgery in extracting the whole dash and having the wiring harness all exposed I was proud when that's what is turned out to be. Found a new Module on ebay for $25 bucks and will be here the end of the week. I'll try and post some follow up pictures for anybody having this problem because they hide the Module up under the steering column mounting bracket and it's not that obvious. FYI for others as well, you do need to pull the steering column to get the dash out and this wasn't too bad but was intimidating at first. Also, make sure you check that you still have your drain along the way as you unplug the harness from the dash cause you might find the drain before ever getting as far as I had to.

For, ASJT3 your right about the radio causing drains as well. I didn't mention in starting this post that I had another 1 amp draw from a bad radio as well. I was able to find that quick and unplug the radio and dropped the 1 amp draw right away. I had read that radios have been pretty common in parasitic drains on GM trucks.