I was starting to have issues with my exterior lights. I would pull the headlamp switch half way out and the tail and marker lights would work. Pull the headlamp switch all the way out and the headlights would turn on but the tail lights and markers would go off.
So went ahead and replaced the headlamp switch. As many have said and shown my wiring harness and plug was a little fried from the heat of powering the headlamps and other lights. Someone had already repaired a couple of the wires. So I have now ordered the headlight relay system from Bronco Graveyard and will install that shortly. (Like $40 with shipping and tax. Thank you memembers for the idea!) That will hopefully help my new headlamp switch last longer. For those who are not clear on this system, it will power the headlights off the battery, not via the headlamp fuse, wiring, and switch. The headlamp switch will now use a little power to simply turn the relay on so the headlamps get power from the battery and go on.
I also figured I would replace the tailight/trailer light relay under the hood, on the drivers side fender well, and by the cruise control. It was original, although working, I thought it might be time to retire it. I do a fair amout of towing so just don't need the drama of no trailer lights at night. Trailers give you enough wiring headaches, I don't need the tow vehicle adding to the headache! Your truck wiring seems to last a truck lifetime. Your trailer wiring seems to last about 3 years! (Oddly so do the tires, surge brake system, electric brake shoes, deck, paint job, etc., etc., etc.) Friggin trailers!
BTW, if you suffer from this situation, your emergency flashers will still work. So just put those on if your tail lights are not getting power due to a bad headlamp switch. That way no one can say they did not see you or your truck or trailer.
(What did you think the flashing lights where saying?)
Now on to my next IDI project, buy and try a new ignition switch and hope it is not the mechanicals going to it! It is getting to a point have to realy twist the key about as far as it will go to start. I know the ignition switch has a little adjustment, but it if starting to go I rather just replace it. I will update when I get it done.