I replaced the headlight switch this weekend and now have no dash lights. New switch appeared to be an exact replacement for the old one (with only a slight change in the dash mount; new mount is same dimensions, but is removeable). The connector is fully pushed onto the switch. All fuses are in tact and as far as I know, nothing else changed.

I do have a few loose bullet connectors under the dash. One (male) goes to the dome light. One (female) puts out current that will brighten and dim the dome light as I rotate the switch ****. Previously when I did this the dash lights dimmed. It is possible that I disconnected something when I was putting in the new switch, but I doubt it.

Has anyone had a similar issue? Is it possible that the switch is somehow different? Any suggestions for diagnosis/testing/repair would be welcome.

 

The switch is probably different. As far as I know, they never put a dimmer on the dome light. The terminal with the dimmer is the dash light terminal. It will have power to it when you turn on the headlights. The dome light terminal will have power to it when you twist the headlight switch to the left until it clicks.
You identify these terminals with a 12 volt cheapo circuit tester.

 

Thanks for the reply. I should have been more specific in that there is a female lead (not connected to anything) that when connected to the dome light puts out current that can be varied by turning the ****. This makes the dome light act like the dash lights.

I suspect that the female lead goes to a male lead to the dash lights, but there are several dangling down. I have identified the ignition wire (pink) that was bypassed when I put in a Pertronix system, the dome light wire (black) that I pulled myself, but there are several others that I am having a hard time identifying. The wiring is old enough so that the colors have faded.

Is there a bullet connector between the switch and the dash lights normally on these trucks? My wiring diagram doesn't show one.

Thanks.

 

I would just plug the dash lights into the bullet connector that has the dimmer. As long as they turn off with the light switch, what's the difference?
If your wires run from the switch straight into the harness like mine does, chances are there will be a connector somewhere between the harness and the lights.
It's probable that some of the extra wires you mentioned were never hooked to anything.

 

1965/66 F100/350: There's two different headlight switches...thanks to Ford and their policy of updating part numbers.

The original switch was: C5TZ-11654-A (Motorcraft SW-439)

Then Ford replaced that switch with: C5TZ-11654-C (Motorcraft SW-718)

There's more *&%$%. The switches for F500 and larger trucks: C5DZ-11654-A (Motorcraft SW-435) can be substitued for the other two switches!

It gets worse = the switches used on 1961/64 F100/600's are different from these three! 1961/64: C2DZ-11654-A (Motorcraft SW-303)

NOTE: None of these switches brighten/dim the dome light. The only thing the switch is supposed to do when you turn the **** to the right is brighten/dim the dash lights. When you turn the **** all the way to the left...that turns on the dome light.

 

Thanks Bill, I'll try the Motorcraft SW-439. Several parts places here (Autozone and Walkers) as well as Blue Oval Truck Parts seem to be selling the same switch as a "universal" F-series replacement. To make matters even more complicated, they don't use Ford part numbers. Almost all of the switches appear the same. The "mount" on the replacement I have is shiny silver metal and includes a removeable bracket that sits between the switch and the back of the dash. The original switch had an integral "mount" where the metal was more gold in color.

I think I have really screwed up here. After the initial replacement, I tested the lights (they worked) and tossed the old junky switch. It just happened to be trash pickup the next day so that part is long gone. This morning, my wipers wouldn't work (blown fuse). I suspect all my fiddling around behind the dash has disturbed some old wires and I now have a short.

So I have traded a functioning switch that didn't dim the dash lights as effectively as I would want for a switch that only turns the lights on and off and no dash lights, plus a can of worms on wiring. The coup de grace was discovering an old t-shirt that the PO had crammed behind the dash panel for who knows what purpose.

I am going to try replacing the switch with the Motorcraft SW-439 in case the first one was bad. If that doesn't work I am going to cram my 6'5" self under the dash with a tester and a few beers and just gut it out. Thanks for your help.

 

Most autoparts stores can cross the Ford and/or Motorcraft numbers over to the brand they sell.

Why don't aftermarket suppliers use Ford part numbers?

They don't want give out "free" info.

Someone might take the numbers to his local dealer or autoparts store, and get the parts there.

In the case of autoparts stores, you can bet the farm that they'll prolly save a buck or two!

Hmm...6'-5" 335 here.

Just wait till you get older and arthritis sets in.

Then try cramming your carcass under that dash!

 

Age old wisdom;
"If it works, don't fix it!"

The t shirt was probably separating the the wires from the ground point. Since you already have it out, you may as well replace it with new. I'm sure NumberDummy can come up with the right one.

 

Hit send too soon. See below for message.

 

So my dash lights and wipers...everything but the dome light are now working. The ratty T-shirt is still wedged in there ("if it aint broke don't fix it" a wise man said), but everything looks good from the driver's seat.

The dome light is a mystery. The lead (f) from the harness puts out 12v. The lead to the light (m) goes to ground via the funtioning bulb. 12v straight to the light lead (m) turns it on. But when you connect the two leads it doesn't work. Reluctanly I am going to cut out and replace the harness bullet to see if that works.

On the dash lights, here are the things I did in case anyone has this problem down the road:

1) Removed the connector at the (chinese) headlight switch and cleaned
the contacts
2) Cleaned the contacts on the voltage regulator
3) Unplugged/probed and checked the accessible underdash wiring for
shorts (there were none)
4) Located a loose connection on the wiper switch, cleaned the connector and plugged in back in. This immediately fixed the wipers.
5) Validated the wiring in place was correct per wiring diagrams from
www.classigcarwiring.com and Jim Osborn reproductions
6) Identified the PO's wiring additions and validated they were properly done. These included stereo wiring, radio wiring and wiring for a trailer brake.
7) Popped the top on a cold beer

Thanks Number Dummy and others for the support.