Faulty Headlight switch ?

Prime Time · Oct 21, 2018

I recently installed dual FF dynamics 8" pusher fans, and took my 75 out for a test run and after I got back I noticed I didn't have tail lights and instrument panel lights , Its not a fuse , I found that when I pull the light switch to running lights,, nothing , then pull the switch to headlights the head lights come on but no tail lights , but in-between clicks on the switch positions the tail lights will come on but not the headlights , Does anyone have an idea if it could be the switch that could be bad ? seems ironic that the switch would go out as I installed the cooling fans , I disconnected the fans to make sure, and same thing, Hasnt been hot enough to see if the dual fan idea works , I will report back on that, thanks guys

SHX669 · Oct 21, 2018

Did you disturb or relocate the ground wires for the headlights ?

DirtDonk · Oct 21, 2018

Very interested to hear how the fans work too. And see more detail on how you installed them.

But in the meantime, my thoughts were the same as SHX regarding grounds.
And yes, it could be the switch too. I call them "coincidental failures" and they seem to happen ALL THE TIME(!) with our old rigs. Unfortunately, cause it makes diagnosing things trickier than they already are!

You could perhaps try disconnecting the headlights to see if anything changes, or adding more grounds (which is a given no matter what anyway) but nothing should effect both the headlights and the tail lights other than the switch.
And only the dash lights are on a fuse. Everything else is protected only by the internal circuit breaker built in to the headlight switch.

Does anything else work wonky at this point? Anything change in the lights when you turn on, say the heater to high?

Paul

DirtDonk · Oct 21, 2018

Oh, and remembering that you said "in between clicks" changes things, that leads even more to the switch.
It's not a common failure I don't think. Don't remember anyone complaining about that. Usually when the headlight switch fails (which is often) it's in the form of the headlights going out momentarily and then coming back on for just a minute, before going out again.
Not with just the tail lights and headlights working intermittently as you manipulate the switch.

Hmm, what about the floor mounted dimmer switch? That's usually the first thing to go on older vehicles, so would not hurt to test that theory.
You can flip it between high and low to see if anything changes with the headlights (does not have any effect on the tail lights), or pull the connector and jumper from power to the lights with a clean and tight wire.
But my money is on grounds or main switch.

To test at least one of the ground theories, run a jumper ground between the core support and the battery. If anything changes, you're on to something.
Where did you ground the fans?

Paul

Prime Time · Oct 21, 2018

I grounded the fans to the core support where the headlights are grounded as they share the same bolt , im wondering since I used the positive wire as a ground to make the fans a pusher instead of pullers that has something to do with it , along with the radiator temp switch which will ground out once it gets up to the 195 degree mark , I unplugged the headlights and still no tail lights , the fans come on when I ground out the temp switch

DirtDonk · Oct 21, 2018

Interesting. I don't know if that can have any effect, but I don't know much about motors vs simple resistance (or "load") circuits. I know enough to know that motors are weird, but not enough to know just how weird.

Sounds simple enough to un-ground the motor wires from the grounding bolts and see if that changes anything. If it does, then you know you're on to something. If not, then on to Plan-B.

Paul

Broncobowsher · Oct 22, 2018

The fact the lights come on at all shows the wiring and the lights and the grounds are all good. Since you can get the lights to work by "playing" with the headlight switch has done the diagnosis.

You have a bad headlight switch.

You can look at grounds, maybe even mess up a good one. You can play with headlights, which are on a separate circuit. But that isn't going to fix the lights.

The headlight switch isn't just 1 circuit. There are 3 or 4 separate circuits all going through that one switch. The headlights are by themselves, have there own circuit breaker. Tail lights are on there own, fused. Dash lights, yet another circuit and a different fuse. And maybe even the dome light.

You have a complete functional circuit. The lights do come on. You are fiddling with the failure point right in your hand, as you are fiddling with the headlight switch. The contacts inside just are not making the connection at all the right times that they should.

Greg_B · Oct 22, 2018

I had so many headlight switch failures I added relays to take the load off the switch... no failures since.

The first time was running 55 through wares valley road in the smokey mountains during in the night time... Scared the crap out of me... I added extra driving lights the next week.

Greg

Prime Time · Oct 23, 2018

I disconnected all my cooling fan wiring yesterday so everything was as before and working , still had the same problem , unplugged the headlights to see if that changed anything , nope still got the tail lights inbetween clicks on the switch ,checked the grounds and their all solid, so I ran down to Napa auto and got the new light switch
(d3zz-11654-a) came back tried to plug it into the harness and it didn't fit , has 8 pins my old one has 7 pins , went back to Napa, went thru the thick ass catalog and found newer style switch from 1983-93 Ford Thunderbird which is the same as my old switch , I found out that if you have a Centech wiring harness like I do the stock switches wont fit , Ordered it and coming today , ill let you know ..........

DirtDonk · Oct 23, 2018

We might have saved you at least one trip if we'd known that you were dealing with a Centech harness. More info is (almost) always more helpful when discussing issues with old vehicles like ours. Maybe you did mention it, but I forgot if you did.
As you found out it's a later model switch, but for a good enough reason in the scheme
of things.

You can still find the old switches no problem (again, as you found out), BUT the harness manufacturers have a hard time finding the main connectors that work with the old switches when they're making the new harness. So the much more readily available connector for the later model Ford switches is substituted.

Supposedly too, the new style switch you have is a better, more reliable version. With your odd failure though, I wonder if we're not going to have to chase down a slightly different version of the failed switch syndrome more often nowadays.
The old ones were stone reliable for 40-50 years, or until you connected brighter headlights. The new ones probably handle the extra current better, but looks like they can still wear out.
Then again, everything build these days seems to wear out prematurely. Something we've had to get used to again and again.

Good luck with this one. Hopefully we hear that all your troubles are behind you after it goes in. We can hope!!!
I'd say you certainly tested the other possibilities thoroughly enough. Looks like it was just another case of "coincidental failures" that we see fairly often these days.

Paul

DirtDonk · Oct 23, 2018

And just out of curiosity, was this a new harness install too? Or have you been running it for awhile already and just added the fans?

Paul

Prime Time · Oct 23, 2018

Paul you have been a huge help as well as the others ,I hastily posted my issue ,so I didn't really know what direction I was headed to resolve it , if the issue isn't fixed today , im sure this thread will get much longer

, Hope this is the end of it The harness was in place when I bought the Bronco 2 yrs ago , it hasn't given me any problems , (yet) I enjoy adding my touches to it and going thru everything so I Know" ,

DirtDonk · Oct 23, 2018

That's good news that it's been up and running very well for awhile already. No indication of future hidden issues then. Some of which can really mess with a diagnosis, if you didn't know that it had been working fine before.
Crossing fingers that the new switch takes care of it for the long term. Two years still doesn't sound like a long life out of the other switch. But maybe it was in place many years before you started using it.
The Centech harnesses have been around for a long time now.

A side note on harnesses. If you have halogen headlights, especially bright ones. Or if you happen to use your high-beams more often where you live, make sure you have the headlight relay harness too.
Takes the load off of the switch and puts it on a heavier duty switch. Which come to think of it, was probably how all the later vehicles were wired to begin with.

Something like this: WH Nightlighter is available pretty inexpensively, or if you're handy with wiring you can make your own.
Your Bronco might already have them even. If you haven't already, poke around for a pair of relays in the headlight circuit.
This would practically guarantee that your next headlight switch lasts the life of the truck!

Paul

Prime Time · Oct 23, 2018

Problem solved ,turns out there was a fused link in the tail light circuit that wasn't part of the centech fuse box wiring , when the light switch was between circuits it would activate one circuit or the other but not both at the same time thanks for all that chimed in

DirtDonk · Oct 23, 2018

Well don't that just beat all! Congratulations on the find.
Does it work with the old switch now then? So you don't need the new part after all.

Glad you found it.

Paul

Prime Time · Oct 27, 2018

I just left the new switch in , so I have the old switch as a back up if I ever need one (or one of you guys ) The universal shroud I added made a good difference as well to keep the smallish radiator be more efficient too , 2 days of driving the fans haven't kicked on yet 195* switch, haven't done much night time driving , so locating a headlight relay or adding one will me my next task

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