Keep going Errors, sounds like you about have the gremlin nailed down. Sorting through a wiring harness with almost a hundred wires in it take lots of patience! I have experienced the dimmer switch problem, driving down the highway at 60 mph and headlights go out. not fun. I had a problem with the potetiometer or that spring looking thing at the front of the switch once. I replaced it with a used OEM I had kept and havent had another problem yet.
Well, apparently all I was doing with the switch working halfway out was 'shorting' the switch and giving power to the dome/taillights from the headlight power feed, so a badly built switch just confused me.
I found that there are multiple power supply wires, a seperate one for dome and/tail lights and it was shorted.
See, common sense says I shouldn't get power to tail or dome if there was a short or blown fuse, which is why this was so annoying to troubleshoot. It shouldn't 'sometimes' work or only work under certain conditions.. but because of the weird switch design, I could make them work if I had the stupid switch out halfway.
If anyone runs into this, Tan/White to the switch powers the dash lights and taillights. I found out that it wasn't supplying any power at all.. shorted a wire and blew a fuse in the old switch. At least, I think, haven't replaced the fuse or checked the wire yet.
Sorta glad I went through this though, apparently the Autozone switches only last a few months, this BWD is definitely a better switch AND it was a few bucks cheaper.
Well, I am glad I found this thread and this post. I am having the same exact problems with my 1989 F250. I thought it was odd that I could only get both headlights and taillights working if I carefully placed the switch at 1 1/2 position. A fraction either way and I lost one end. The shorting between the headlight terminal and the taillight terminal makes sense.
I have had my truck since 1998. I drive it very little in reality, pull boats, snow machines and haul stuff. I have had no problems with lights until about a year ago and Boom! same exact symptoms as the OP. I figure no problem, change out the switch. I have a Motorcraft switch from a parts truck. Pop it in and… NO CHANGE!! I think maybe two bad switches so I order a new one, turns out to be a “Standard Motor Products” T-Series DS268T switch. I plug it in and same symptoms. I read some forum posts and find many issues related to the nine wire plug at the switch. I order a replacement and install it (cut, solder and heat shrink). Plug in the NEW switch and I can’t get it to “short” and make both lights (head & tail) come on. I plug in the second Motorcraft switch and I can get this one to “short”. I got lights! … sort of…
I read my wiring diagrams and look at the switch to come up with an idea. Nothing happening up there. I read some forum threads and I find this one. I have some questions about the above post:
My diagram shows that the Tan/white wire comes from 15Amp fuse position #4. I am seeing that the Brown wire goes to the marker lights and taillights. The Blue/red wire powers the instrument panel/dash lights. The Blue/red gets its power through the rotating dimmer wheel which is powered directly from the Brown wire. No power to Brown, no power to Blue/red. Are you saying that I am getting no power from Tan/white which in turn means no power to Brown? What was your fix?
What do you mean “blew a fuse in the old switch”. I see no indication that there is a fuse in the switch, only the fuse box. Do I need a new switch (which one, BWD?) or just replace that one wire?
Thanks for your post! Hope you are still around! Hope you have it all worked out!