If not one thing, its another...

It decided to blow the fuse that powers all the dash guages and the turn signals today. Trucks still starts and runs fine with it blown. I put a new fuse in, and it was okay just sitting there... gauges turn on, turn signals work (with the key in the on position). But, as soon as I actually start it, it blows in about a second or so. So, it's something that doesn't get power till after it's running, not just when the key is in the run position. Any ideas off the top of your head what that might be?

I do have a factory service manual, so I can hunt down the wires, but was hoping someone might know before I start digging into that.