I have a 2007 6500 4WD. I bought it a year ago with 325 hours on it. I used to see the manifold heater light come on when I first turned on the key, now it does not, and when temps are in the 20's, it has to crank a lot to start. I found the manifold heater and light on the wiring diagram, and I think I have the right timer relay-blue, four prong, mounted high up inside on the left rear of the engine compartment. I see on the wiring diagram that the timer sends juice to the manifold heater, but that sure doesn't seem right, because the wires from the timer relay are a lot smaller gauge than the wire going to the heater, anyway the wiring diagram said they had a 10 amp fuse in line. I checked all the fuses in the fuse panel. They were fine. None are listed as the heater fuse. But behind that fuse panel, there were two fuses taped to the wiring harness. One of them was a 10 amp that was blown. I replaced it, I still do not see the heater light come on- however, the engine was warmed up and I'm not sure if that's a factor. If anyone can shed the light on when this heater is posted come on, how long it is supposed to come on, whether engine temperatures a factor, where the components are located, where the heavy wire going to the heater goes, etc. I sure would appreciate it. Thanks, Doug