Well, after several hours of weeding through wires, I replaced my temp sender and my temp gauge finally works (sort of). For the first time, the needle actually moves on its own, but it caps out at H when the engine warms up. It's a 70 blazer, and I've got a new crate 350 in it, with long-tube headers - could the headers be warming up the sender that much more? Or does it sound like maybe my gauge resistor is bad? (it's the only thing I haven't replaced really).