My preheat system does some wierd things every now and then. For instance, when the truck has been sitting all night into the next morning, and the outside temp is, say around 50 or so, it won't cycle the heaters. I know it's supposed to be below 59 F for the heaters to cycle, but it takes mine to be below 50 for them to cycle. I have an early 91, by the way. Some times, when it's been sitting for a while and the engine has cooled to the point where the thermisor says "heat em up!" (on a really cold day) then the WTS light will come on for about a second or so, as do the relays. And sometimes, during a "normal" cycle, they won't cycle long enough. I timed out about 5. 5 seconds one time. Is there something funky here? I have replaced my thermistor twice with no change. I've even cleaned all my connections, and it's still sporadic! I just don't want to be stranded one morning when it's -5 outside and I don't have any where to plug in at. It will start, but it takes about 5-10 minutes and is really hard on the engine (I've tried to see if it would start by skipping the preheat once). Sorry this is long, but it's been bugging the crap outta me for the past couple years. Any advice? THanks!
jaynes