I have a 92' power wagon 250 with the 5.9L 12V intercooled, A/C, power windows, locks, and lots of electrical problems! My biggest problem right now however is that my over drive will disengage at speeds of 75MPH or not engage at all. I noticed that the problem happens when it's moist or wet out although it still occurs when everything is bone dry, also the tachometer will not read true or not give a reading at all while the problem is happening. But if i step on the brakes the tachometer will work but it still wont shift. my battery voltage drops a considerable amount as well sometimes down to 10V, all these problems come and go at the same time. please help!! I bought a book for the truck but it's useless. (no diesel info at all)