1969 Mark III Headlight Issues

Hey Bill,
Greetings from east Texas. Just when I think everything is working correctly a snake raises it’s head. On our Mark III, I installed a NOS headlight switch (w auto/dim). The headlights had been flashing off and on after 5 minutes of driving. The new switch cured my flashing headlights. Now after 5 minutes of driving the dash lights and park lamps/tail lamps go to flashing. This has never happened before. The auto/dim feature also quit working. This had never been a problem before. Auto dimmer had always worked perfectly. What the heck is it NOW? PS, I just bought a bucket list car, a 69 Marquis convertible. Dark Orchid and white. It’s a solid scab now but in my hands she’ll return to glory. Does Chris have anything on hand for a 69 Marquis?
Patrick
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Greetings Patrick –
Flashing headlamps is usually caused by a fatigued circuit breaker within the headlamp switch and /or upgraded heavy power draw headlamps. The new switch has evidently corrected that issue but these switches also have another breaker inside for the park , tail lamps and dash lights. The dash lights also have a 4 amp fuse to protect that circuit separately. Because the new switch has corrected the first issue it would appear to me that the NEW switch is faulty or a wiring problem to the park lamps and the Automatic Headlamp Dimmer was created somehow during the new switch installation. The switch installation and wiring should be examined and if nothing is visible the old switch could be plugged in to see if the problem reverses back to the original headlamp problem and the new park lamp problem disappears. If the installer was inexperienced, the dash light dimmer rheostat area at the switch possibly could have been damaged etc. I am assuming that the wiring at the tail lamps, park lamps and license plate lamp. have NOT recently been disturbed and are now shorted out. Please let us know what you find out with this interesting event.
That 1969 Mercury sounds beautiful – but it’s going to be a hard one to find parts for, feel free to check with us as you needs parts – we may be able to point in the right direction.
Sincerely,
Bill
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Thank you Bill,
I have the original FOMOCO bulbs in the headlights. Nothing disturbed or altered in my Mark III. NO whack job on any of the wiring or plugs, all factory original. I installed the switch with the battery disconnected. The auto dim no longer worked after I installed the switch. I had no issues with the dash/tail/park lamps until a year later now. I have driven the Mark at night and they were not flashing until last night. I thought for the last year I could deal with the issue of a non functioning auto dim even though I’m a perfectionist. Can I examine this circuit breaker within the switch ? I am extremely mechanical.
My best to ya’ll in Florida! It’s still 100 degrees and muggy here in East Texas.
Patrick
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Patrick –
For starters – we would suggest swapping back to your old Switch and seeing if your issues remain the same.
Sincerely,
Bill
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Bill –
Do you guys have a used switch for the Mark III? I plugged my old switch in and the dash lights work but the headlights flash again, the auto dim works! I called my engineer
buddy in Kilgore and he told me he thought if I added relays it would take the load off the switch. I have no idea what that is all about but had to run that by you guys. My GAWD I want to pull my hair out. I love my Mark III but sometimes.
Pat
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Hi Pat –
I’m glad that you decided to follow the advice on our Blog to swap in your old headlamp switch as a test. You have now proved that both of your switches are evidently faulty but in different ways as I suspected. Your engineer friend is correct in that adding relays will transfer the headlamp load away from the switch and its circuit breaker to a relay with a separate fused battery source. The headlamp switch circuit breaker would then only need to operate the lower amperage draw relays instead of the higher draw headlamps. These relays are added usually to vehicles that have had higher amperage draw headlamps installed in place of the original seamed beams. In your case however the success of adding relays depends on how much your breaker has deteriorated inside your switch. This of course we do not know. Also for your information I have seen a poor connection at a headlamp switch pin become so hot that the heat was transferred to the breaker inside and was enough to open the circuit. This is always easily discovered because of the visible melted plastic at the switch electrical plug. Show all of the above information to your friend to see if he agrees.
Headlamp relay harnesses with relays and the necessary fuses or breakers are available in kit form from many aftermarket headlamp suppliers or are improvised on site as necessary by local competent electrical shops or the vehicles owners.
Headlight Switches with the Autodim feature have to be sent into us for Rebuild – please contact us to make those arrangements.
Sincerely,
Bill