Headlights shut off after a five to ten minutes of running

[deathsled]

Sorry to revisit this issue, but it fell off of my radar a while back.  I currecntly have a pair of halogen headlights on the car which I suspect draw a lot of power.  I bought a pair of Cibie headlights and also a wiring relay from Daniel Stern quite a while ago as the solution to the problem but made no movement toward installation as I became obsessed with trying to survive Covid at the time which derailed a number of plans.  I seem to recall someone offered a simpler solution by using a 69 light switch?  Can anyone shed any light (pun intended) on the situation?  If it is a 69 switch, how easy is it to substitute for the 66 switch and does it fit without any modifications?  I am driving the Shelby to the MCACN which I can do during daylight on Friday.  Coming back on Sunday will be the problem as it will be dark when the show ends and the cars are released.  Thank you for any input.

Richard E.

[deathsled]

Just ordered a Motorcraft light switch for a 66 from O'Reilly's Auto Parts.  It will be available by tomorrow.  I was surprised to see how easily available it was and that Motorcraft made them.  It looks like an easy replacement. (Thank you YouTube).  I will buy it and see if it fixes the problem.  At least for now.

https://www.youtube.com/watch?v=iDyxciegjtI

https://www.oreillyauto.com/detail/c/motorcraft/engine-sensors---emissions/body-switches/headlight-switch/d8019a4235ad/motorcraft-headlight-switch/mot0/sw441/v/a/15191/automotive-car-1966-ford-mustang?pos=2

[shelbydoug]

I don't know if the 66 is the same as a 68 switch but the 68 has a built in circuit breaker.

Going to halogens in mine increased the amperage and would blow the breaker.

I replaced the switch with a Motorcraft and have never had the problem again.

[deathsled]

Thanks Shelbydoug.  I am giving it a try to see what happens.  Zray was on this site a while back and suggested the Cibies which he had on his 66 Shelby and lauded them for their brightness and reliability.  I have the kit but crunch time as the show looms.  Friday is my check in day.

I understand that some show their cars with the drop dead original back-in-the-day headlights that don't even work anymore they are so old.  That is hardcore.  But I tip my hat to them for creating the original feel of the car on every level right down to the Ford script in the headlight which I believe was engraved into the glass.  So cool!

[shelbydoug]

Thanks Shelbydoug.  I am giving it a try to see what happens.  Zray was on this site a while back and suggested the Cibies which he had on his 66 Shelby and lauded them for their brightness and reliability.  I have the kit but crunch time as the show looms.  Friday is my check in day.

I've got Marchals with 100/80 H4's and the '68 Lucas "square 8's" with 100's in them.

If I get too close, I can melt your bumper. The Lucas' run their power off of the main switch.

There's a lot of amperage running through it.

With time the circuit breaker gets a little sensitive although there are some service records under new warranty for headlight switches. There might be a service bulletin for them also?

I haven't looked at them in a while. You could look at Coralsnakes web page and see if he has those posted. It would be the same issue as for your '66.

I think that the Motorcraft service switch is upgraded?

[68blk500c]

In a pinch situation, you can unplug one (right side) headlight to cut the draw in half and limp it home on the left side light.  Fog lights that are wired correctly can assist, too.

[texas swede]

The 65-68 headlight switch has a 12A trigger and the 69 a 18A trigger.
Normally 67 Shelbys have the shut off problem as the trigger is at 12A
and it has 4 headlights. On a 66 it will be fine with a 12A, if as you said the Halogen
bulbs don't draw to much current.
Many years ago, in Sweden, I almost hit a moose when the headlights (4 high beams)
on my 67 shut off. The brakes really were tested that time.
Texas Swede

[Pcunder]

TexasSwede is right.

The CB (circuit breaker) inside a Mustang/Shelby/Boss headlight switch can "trip" when overheated but will reset once cooled off. I assume you can "blow" one from constant abuse or maybe just age and then, a new one is in order... I learned a lot while troubleshooting lighting gremlins in a 70 while swapping with 69 parts.

Got this CB info straight from the Ford Shop Manuals for Mustangs

Year        Amps
-----------------------------------------------------------------------------------------------------
66           12       (Falcon also)                                        18=   Comet, Fairlane
67            ?         No manual
68           12       (Falcon also)                                        18=   Cougar, Fairlane, Montego
69           18       (also Cougar, Fairlane, Falcon, Montego)
70           12       Falcon/Maverick also                            18=   Cougar, Fairlane, Montego

69 CB rating IS higher than the 70 (due to supporting 4 headlights vs 2) but is exactly plug & play.

FYI: there are multiple CBs in each Headlight switch & not only for lighting, like horns!

HTH,

Phil

[deathsled]

They do shut off but are able to be switched back on after a couple minutes.  Maybe the Motorcraft is upgraded to handle to load.  I will find out tomorrow.  Thank you guys.

[C6ZZGT]

Start with the switch BUT also checking wiring for good connections and grounds . The relay kit will be the way to fix it for good mind you.

[shelbydoug]

Start with the switch BUT also checking wiring for good connections and grounds . The relay kit will be the way to fix it for good mind you.

Yes but in my case, the switch alone corrected the issue. The separate relay was not necessary.

Traditionally however the recommendation from any of the halogen light manufacturers is to put the lights on a separate relay.

[deathsled]

Turned out that O'Reilly's switched the switch on me from a Motorcraft to a Standard. A so called bait and "switch." I heard a favorable review on Standard so went with it. A bit cramped behind the dash to get to the switch button to push it that releases the stem. For a minute I was thinking I might have to take the whole bezel off. I did not. Persistence is the key. Once the light stem is pulled, there is a very large phillips tip bolt to unscrew, so large and wide that I used three butter knives put together as one and it worked. Difficult to wrestle the switch out. Sticking one's right pinky finger into the switch through the dash worked to push it away and pull the switch down with the left hand. The rest was easy. Pry away the connector at the base with a butter knife and it pulls away. Install the switch and stuff it back up under the dash. Screw back in the bolt and reach back and push on button as you push in the needle-like stem on the switch.  All done while the negative is disconnected from the battery of course. Turned out the old switch was a Motorcraft.  Must be about 20 years old when the car was being reassembled though not much time on it using the headlights. Maybe it aged out if such a thing is possible with electronics.  Will see how well the new one works. I do have a relay setup. Just want it to work to get me back from the show. I will stress test it tonight if the wet snow stops and the roads dry. I will keep y'all posted who are interested.

[deathsled]

Did a 20 minute stress test this evening driving the neighborhood.  Problem seems to have resolved.  The headlights were winking out after 10 minutes or so.  Therefore, MCACN will be a drive in and drive out for me without the trailer drama...

[98SVT - was 06GT]

If your lamps put too much draw on the switch and it fails again you can add a relay. Basically the switch activates a low amp drawing relay whose contacts handle the big draw. We did a lot of all night rallies in my Road Runner and I had rewired my halogen bulbs so low and high beam were on at the same time. That and an extra pair of driving and a pair of fogs. 3 relays 10ga feed 14ga to the lamps never a problem.