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Discussion Starter #1
I had to evacuate my home last week in a hurry because of two approaching wild fires, So I took the 72 Ranchero GT 4 speed Cobra Jet and left the others behind and hoped for the best. I was able to return home yesterday and found that all was fine , no damage to home or cars. On my return trip home from the Central Coast of California which is about a 5 to 6 hour drive to my home in the Mountains of San Bernardino the lights on the car started acting up after being on for 4 hours. First the dash lights started to flicker, then the tail lights. I pulled over and searched for a loose wire or a bad ground but I was unable to find one. I did notice that the back side of the interior switch to the lights was very hot, and I am wondering if this is normal after driving for four hours with the lights on and could it being so hot have been the cause of the lights going out?
 

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Sounds like you've either got a short in the lighting department or the wires just arent up to the task of flowing enough current to get the job done. Either way it's gonna be a labor intensive problem to solve, but start at the switch first and go from there.
 

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Do you have regular sealed beam lights, or did you upgrade to H4/Halogen lights?
 

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If they are Halogen O.E. replacements...which surely they are...mine still had factory incandescent high beams(Westinghouse)...imagine that...I upgraded all the lights to halogen replacements... Well, after driving for a while...the headlights would flicker...that's not a good feeling...if I used the high beams...they would flicker in about 2 minutes...untill I turned them back to low beam. The old system was designed for incandescent-low wattage bulbs...the light switch and wiring is not made for halogens. About the only logical choice you have is to relay the headlights, if you know how to wire a relay...it's a breeze...power and ground...switched posts going to the high or low beam post on the bulb...and the switch post on the relay is the factory headlight wire...since it pull so little amperage to switch a relay...it will take a lot of load off the switch...which is always good. I had drawn a diagram out...but my hard drive crashed and I lost it...I used 4 relays on mine. Now I'm running lined H4 upgrades from pepboys.com...they are really a good quality replacement...glass/metal...and they are a good price...if you ever wanted to upgrade. Mine are extremely bright now...I can actually see the road ahead of me now...:D
 

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Go through your dash wiring harness and clean your grounds. There are multiple throughout the 14401 harness attaching at various points on the dash steel frame, IIRC is one near the light switch attached to the metal frame of the dash, there is also the steel support rod at the center of the dash to the firewall and then there is one on the right side. Those and the radio retainer clip.

But...

I installed a new 12 gauge wire that I soldered onto the ground wire at the point nearest the light switch, connected that lead to several of the other grounds, ran another lead to the tail lights and tied in on those grounds at the left rear, and combined all those leads at the dash and ran a single 12 gauge black wire out to the negative battery terminal. For that I replaced the negative battery cable with one from a '72 Mustang that had the additional 12 gauge wire integrated in the battery clamp and crimped that wire using the supplied crimp type connector. That solved a multitude of intermittent electrical issues in my '72.

Your light switch getting hot is a sign that you are having a ground issue. I ran my '72 GT 4 Speed with that issue quite a while and eventually cooked the light switch. Since I added the direct ground lead out to the battery (this was about 25 years ago) I haven't had any issues since then. OBTW, during the current restoration I have actually added 7 steel blocks welded to the chassis in various places and have strung a ground lead that interconnects the doors, back body at the tail lights, at the cowl for interior and engine side ground straps along with the fenders and headlight / radiator support. Every electrical issue I have had with that specific car has always resolved to a bad or disrupted ground. JMHO
 

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Discussion Starter #7
I replaced the headlight switch and the problem stopped.
Thanks you all for your input.
 

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Suggest you still might want to clean your grounds from the dash frame to the cowl at the least. Been there, done that with the switch and lost a few in fairly short order for the same symptoms. Also, periodically "feel" the bezel that the light switch rod passes through. If you start feeling some significant warmth you are building to another failure. JMHO, and Good Luck!!!
 
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