1978 LN8000
 

Hi all, Could anyone tell me where I can find a wiring diagram and perhaps a wiring harness for a 1978 LN8000?
I have about the strangest problem I have ever seen. I had used the truck about a month ago and then parked it. I went to start it and the batteries were dead so I figured I would jump it and get it going. Hooked up the jumper cables and all the lights came on and the light switch was off. Messed with the light switch and they would not go off so I unplugged the switch and they stayed on. I am a bit stumped. Has anyone seen anything like this? Thanks