why is he re-wiring them? were they not working at all before? do the backup lights come on now because he was messing with them and screwed up or he started to work on it because that what it was doing? first thing i would have looked at is check the grounds.
The best I can do is from the 1981 wiring diagram under something called the L-Series
trucks but there's a guy here who may have a 1980 diagram, have your husband look at this
and let us know if it doesn't work for him, OK?
The image is 2808 x 1313 pixels, make sure your browser doesn't shrink it on ya.
Thank you for the diagram...it is just what my husband was looking for. He thinks it will help him immensely. Thanks for taking your time to help us...he is almost finished with combining corn...just about 4 more days. This is the truck we haul the corn in to the mill.