The biggest problem I had was with the car alarm LED. That thing was tie-wrapped every 3 inches or something, and I eventually ended up cutting it.
Anyway, my warning is that the harness that Crutchfield sends you (and probably all the universal Isuzu harnesses) do not have the ground wire attached to anything. The ground goes through the chassis.
So, just plugging in the plug isn't enough. Don't panic when you plug it in to test it and it doesn't work. You must reinstall the radio into the dash to get it to work. (Or run your own ground line.)