Flickering headlights.

[JoeD]

Hello,
I'm new to this board, and wanted to start by saying I'm glad to find a forum dedicated to owners of my vintage T-bird (1965).

I have an annoying headlight problem that just doesn't want to go away. The headlights flicker (cycle off and on) when the high beams are on. I had thought I fixed this problem a couple months ago when I replaced the headlight switch (with a brand new switch). The problem seemed to have been resolved, until last Thursday. The problem returned after an extended night drive (1.5 hours). The lights started flickering again after I had the high beams on for a few minutes.

I've noticed that whenever this problem happens, the headlight switch gets quite warm to the touch (which is why I had assumed it was a bad switch the first time around). Before, it happened even on low beams. Now it only seems to happen when I have the high beams on--I verified today that within five minutes of turning on the high beams, the circuit breaker in the switch starts cycling the headlights off and on.

Today I also looked at the dimmer switch (the foot operated switch that switches the high beams). It looks old (probably an original), but the wiring connectors looked clean, and that switch didn't get warm.

I've heard that a corroded connection could cause this problem, but I don't think any of my connectors are the problem--the lights don't look dim at all. I didn't check with a multi-meter, but judging by the brightness of the lights, they appear to be getting a proper 12 volts. I would have expected dim headlights if there was a bad connector or ground.

I'm kind of out of ideas here. The only two things left that I can think of are:

1. There's a high output halogen bulb on the driver's side low beam. One theory I have is that that halogen bulb is drawing more watts than the switch is designed to handle, and with high beams, I exceed the current carrying capacity of the switch.

2. Long shot, but maybe the voltage regulator is letting the voltage get too high. If the voltage going through the switch is too high, maybe that's overheating things.


Does anyone have any suggestions? Has anyone else had problems with using halogen headlights in place of conventional sealed beams? Any suggestions would be greatly appreciated, since I don't want to be without headlights at night.

Thanks,
Joe

 

[Joe Vandatta]

I have halogen headlights in my 66 and it has not presented a problem. If you have a voltmeter ck to see if it is within limits. If it is okay I would still suspect the dimmer switch. The headlight switch will get warm due to the ressistance in the panel light bright-dim control, this is normal.
Good luck,
Joe

 

[JoeD]

Thanks. I have a new dimmer switch on order, and when it arrives I plan to see if it fixes the problem. The old one does look pretty old. Based on a date code I saw on the old headlight switch, it appears to be a service replacement from the early 1970s (the engineering code starts with D0...). If the dimmer switch is at least that old (it sure looks it), I suppose that could be an issue.

Should the dimmer switch get warm at all? One of the things I checked yesterday was to touch the dimmer switch with the high beams on. By the time the lights started flickering, the switch was slightly warm to the touch. Not hot like the headlight switch, but noticeably warm.

Thanks,
Joe

 

[Joe Vandatta]

Joe,
I think you are on the right track, I have had dimmer switches that caused the problem you have. The headlight switch gets warm as I said due to the resistance in the rheostat which is insulated. The dimmer switch should not get warm. Since your lights are bright I think your ground connections are okay.
Joe

 

[JoeD]

Thanks! I'm inclined to agree--if there was a bad (corroded) connection, there should be resistance and a voltage drop at the headlights. To be sure, I should double check with a voltmeter, but judging by the brightness of all four bulbs, I can't imagine there's much, if any, drop.

I'm still waiting for that dimmer switch to arrive, and will give you an update once I install it. Even though I have to wait, it's often easier to mail order old car parts than go to the local auto parts store. Ask for parts on anything over 20 years old, and you get the deer frozen in the headlights look. Either that, or the brush-off because it requires going back to a BOOK instead of looking it up on the computer.

Guess that's part of the challenge, hunting down those parts. Jay Leno once put it well--he likes driving cars where it's a major accomplishment just arriving at the destination. Ever read his column in Popular Mechanics? Jay's one celebrity I'd love to talk to (well, also Melissa Joan Hart or Courtney Cox, but I digress). Jay's one of the few Hollywood types who's still a regular guy.


Joe

 

[Joe Vandatta]

Joe,
You will not get the cold shoulder at
www.tbirdparts.com Or phone 800-232-6378.
You will find them to to nice guys and there is no state sales tax in Oregon where they are located.
I am a Jay Leno fan too--he is quite a guy. did'nt know he had a colum in Popular Mech.
Let me know if the dimmer switch does the trick.
Joe

 

[JoeD]

I replaced both the halogen headlight with the conventional sealed beam bulb, and also replaced the dimmer switch. UPS must have had a different driver on my route, since the packagage with the dimmer switch was delivered to one of my neighbors, so I didn't get it until after I installed the non-halogen bulb. This gave me a chance to try the solutions independently of each other.

With all sealed beam headlights on the car, the headlights still flickered on high beams. So much for the lower current draw of non-halogen headlights. A check of the old dimmer switch revealed that it was quite warm to the touch. Not hot enough to get burned, but uncomfortably hot. Out of curiousity, I felt the headlight switch and accidentally touched the rehostat (the part that dims the dash lights). Ouch! Now I know what you're talking about with the headlight switch normally being warm.

In dismay, I put the car away to wait for the new dimmer switch. Two hours later, my neighbor stops by to drop off the errant package. Inside was a brand new Motorcraft dimmer switch. Hopes rising, I set about replacing the switch. Naturally, the replacement switch, even though marked with a C0 Ford number, seemed to be a little different than the factory original dimmer switch. It plugged right in, but the base was a little narrower, which forced me to drill a new hole in the floor so I could mount the switch. Why do the jobs that look the simplest become so complicated???

Anyway, I tried running the headlights on high beams with the new switch, and for the short test I had time to run, the switch never heated up, and the lights never flickered. I'll know better once I have more time to let it run on high beams for a good long time.

On a side note, I tested the voltage output at the headlight connector while replacing the bulb. On battery voltage (engine off), I saw about 10.75 volts (this was before I installed the new dimmer switch). I couldn't find any literature that would tell me if that's ok or not. I assume there should be a little voltage drop because of both the length of wire involved and the circuit going through both a headlight and dimmer switch. Don't know if that's enough to give me a 2 volt drop or not. The light is nice and bright, though, so that I'm going to assume that everything is otherwise ok.

Thanks for all your help and suggestions. I may not be out of the woods yet, but the future's looking a lot brighter (no pun intended).


Joe

 

[Joe Vandatta]

Joe,
I think you've got it. The voltage drop is normal and I think the problem is solved.
Let me know what the results are after a long drive.
Joe

 

[RichTXN]

I have a related problem on my '64. My headlights do not flicker or go out, but the dash lights come on when I turn the headlights but go out after five minutes or so. Then I can't get them to come back on until I turn off the lights for a half hour or so.

My guess is that something is heating up and shorting the lights, but I can't think of what to do to fix it.

 

[JoeD]

The problem appears to have been fixed. Last Tuesday I took the 'Bird into work for some exercise, and after work I stopped by a friend's place to help him change a starter solenoid on his '93 Ford Ranger. Long story short, after changing the solenoid and hanging out afterwards (his wife made some awesome beef stew--guess I'll work for food ), I was headed home after dark.

He lives out in the country, so I spent 40 minutes driving on some very dark country roads with lots of high beam usage. The lights never flickered, and when I got home, a check of the dimmer switch showed that it didn't heat up like before. I think the problem is solved.

Regarding the gentleman whose interior (dash) lights are flickering, I believe they're also protected by the headlight switch circuit breaker. A look at my owner's manual shows two circuit breakers are built into the headlight switch, one for the headlights and I presume one for the interior lights (I think the tail lights are on the same breaker as the interior lights). In my situation, even though the headlight circuit was the one having problems, at one point my headlight switch overheated so badly that even my tail lights and interior lights were affected. If it wasn't so dangerous, it would have been funny to watch the various lights cycling on their independant time scale.

The easiest (though not the least expensive) thing to try is to substitute a known good headlight switch and see if that fixes your problem. In my case, the original headlight switch must have also been bad (in addition to the dimmer switch), since it would get so hot I couldn't touch it (even after only 3 minutes of use). After replacement, it still heated up, just not as bad as before (which made me prematurely declare victory). As Joe (the other Joe ) noted, your switch should get a little warm because of the dimmer control for your dash lights. However, I think Joe would agree, unless you actually touch the dimmer control itself, your switch shouldn't get so hot you can't touch it.

If a new switch doesn't cure it, my suggestion is to do what I did--follow the circuit and find anything else that may be causing excessive resistance--this includes all connectors (plugs), and any grounds (not sure where, but there should be a ground wire connected to a metal section of either the dash or some other metal body part). Any loose or frayed insulation would be fair game, too. I'd suggest getting a wiring diagram.

Good luck--I can sympathize since electrical problems are among the most frustrating car problems to diagnose. Often, the actual repair is easy, it's finding the problem that's hard. That's a big reason why my newest car is a 1981 Mercury Zephyr. Fewer electrical gremlins to fight. A co-worker (different one) at my job has a '96 Jeep Cherokee, and he has an intermittent misfire that several different mechanics can't track down (two different dealerships and an independant mechanic). From my entire childhood and adult experience, I've yet to see a misfire that couldn't be tracked down and fixed in a pre-computer era car. I remember my father doing a lot of work on his cars (it seemed 90% of which involved fiddling with temperamental ignition points), but even though he only had a 3rd grade education and no formal mechanics training, there was never a problem he couldn't fix. Just wish they'd build cars like that today.


Joe