Found flashing headlights culprit - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 05-11-2019, 08:47 PM Thread Starter
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Found flashing headlights culprit

A few weeks ago I was driving at night and my headlights began flashing on and off every few seconds. Not diming either, I mean completely on and off sometimes remaining off for seconds. Luckily I made it home and didn’t get in any accidents. Since then I changed the headlight switch, and voltage regulator, thinking it was that. Last weekend it happened again but even further from home. I accidentally hit the high beam switch and they came on and stayed on. I thought maybe the dimmer switch was the source of the problems.

Fast forward to today and in the middle of replacing the high beam switch I discovered the plug is melted to the old one. Looks like I found my culprit.

Question now is it a matter of just replacing the switch? Or do I need to follow and trace the wires to another underlying problem?

The high beam switch is super old like over 20 years for sure. The only thing I can think is maybe stressing the system is the headlights, but they’re only the OEM looking Scott drake bulbs that illuminate slightly better than stock ones.
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post #2 of 15 (permalink) Old 05-11-2019, 09:08 PM
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Quote:
Originally Posted by xela.zue View Post

Fast forward to today and in the middle of replacing the high beam switch I discovered the plug is melted to the old one. Looks like I found my culprit.

Question now is it a matter of just replacing the switch? Or do I need to follow and trace the wires to another underlying problem?
If the plug is melted to the switch, I'd suspect the issue began with wires touching metal. You're lucky it didn't start a fire. When you replace the switch look for frayed wires or worn insulation. Switch might be old, but I'll bet the wiring is older.

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post #3 of 15 (permalink) Old 05-11-2019, 09:24 PM
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consider using a relay ,it's how they should have been
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post #4 of 15 (permalink) Old 05-11-2019, 09:39 PM
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IMHO, anything known to be bad, should be replaced. Almost any mustang parts supplier has a headlight wiring connector pigtail that can be spliced in for replacement. Also, I believe the head light switches from 1965 1970 will work for your application. The switches were known to heat up, and make and break contact internally, causing even more heat, and eventually resulting in the the headlights flashing-on and off as connection was broken- and then connection was reestablished when cooling down just seconds later. This situation is also compounded by the fact that a lot of original wiring is now 50+ years old. Also, I think most people will replace their switch with one for the 1969 model, as it was built a little more heavy duty, to handle the four headlights on that model.
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post #5 of 15 (permalink) Old 05-11-2019, 09:51 PM
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An no matter the brand or type, incandescent, halogen, a 50w bulb is only going to draw 50w. Halogen gives off more light using the same 50w that the incandescent did.

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post #6 of 15 (permalink) Old 05-11-2019, 10:04 PM
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While the melted connector may be the culprit, the headlight switch is known to cause just as you described as well. All of the lighting load passes through the switch and they go bad over time. As previously suggested, using a relay to get the load off the switch is desirable. It will also make your tail lights brighter since the headlights are no longer pulling so much current through the headlight switch.

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post #7 of 15 (permalink) Old 05-11-2019, 11:22 PM Thread Starter
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Just to clarify, it’s wasnt the headlight switch and plug connector that were meleted together. it was the dimmer switch on the floor, the one you hit with your foot for the high beams, that was melted to the plug connector. Also the wiring is new, it was rewired a few years back.

I’m going to try a new dimmer/high beam switch and see if that solves things. Obviously I’ll need a new plug since the current one is melted
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post #8 of 15 (permalink) Old 05-11-2019, 11:30 PM
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Normally the internals of a high beam switch contacts will generate excessive heat when going bad and transfers that heat to its corresponding terminal melting it. If the current of the circuit is too high the CB in the headlight switch would trip. The rule of thumb with regards to melted fuse holders and terminals is due to poor connections not excessive current as it would appear.

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post #9 of 15 (permalink) Old 05-12-2019, 02:07 AM
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Many an older vehicle is subject to this same problem. Resistance increases in the headlight circuits due to corrosion and/or poor connections. The headlamp switch is usually blamed first because it has an internal circuit breaker that trips because of the resistance. Headlight switches do get old and their internal resistance can add to the issue. So sometimes a new switch can temporarily fix the problem. Most often the main issue is elsewhere in the circuit, like the headlight ground connection, and it continues to get worse to where the new headlight switch isn't a good enough bandaid.

It's not unheard of to lose the high beam switch. Since the connector was melted you would hope that was the main point of high resistance. But you really want to check the rest of the system too. Using a multimeter to measure actual resistance might show something but a better method is to look into "voltage drop" testing. These days there are cheaters with IR cameras like a Flir C3 or C2 who can just look at the electrical system with them and suss out bad connections just by the heat signature.
I seriously want one of those C3's but simply can't quite justify the price. Not yet anyway. I have been hearing about "Load Pro" leads making bad connection testing a bit easier and since they are about a tenth of the C3's price, I bought some. They should arrive next week. I'm looking forward to seeing if they are worth fooling with. The YouTube hype says they are.
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post #10 of 15 (permalink) Old 05-12-2019, 03:01 AM
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Do those Load Pro leads work with regular dvms?
Will have to go look them up.
ETA, seems they do. But the reviews I found on Youtube were horrible, as far as either actually reviewing(first review I found was a guy reading other people's reviews) and put to sleep boring.
But I think I need to add them to the want list.
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post #11 of 15 (permalink) Old 05-12-2019, 07:12 AM
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I never come across one of those devices.If I need to add a load of 1/2 amp or less (which is what the ioad pro draws) I have always used a test light usually this type of testing is a must for pin testing an inoperative electronic component as an ohm meter test doesn't do these types of tests any justice.. But by far the most accurate best method for testing circuits is in a live condition. For example low beams may draw 4 amps when turned on. This is obviously a greater number for loading the circuit than a 1/2 amp and will clearly exploit any poor connections.

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post #12 of 15 (permalink) Old 05-12-2019, 08:17 AM
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Quote:
Originally Posted by GypsyR View Post
Many an older vehicle is subject to this same problem. Resistance increases in the headlight circuits due to corrosion and/or poor connections. The headlamp switch is usually blamed first because it has an internal circuit breaker that trips because of the resistance. Headlight switches do get old and their internal resistance can add to the issue. So sometimes a new switch can temporarily fix the problem. Most often the main issue is elsewhere in the circuit, like the headlight ground connection, and it continues to get worse to where the new headlight switch isn't a good enough bandaid.

It's not unheard of to lose the high beam switch. Since the connector was melted you would hope that was the main point of high resistance. But you really want to check the rest of the system too. Using a multimeter to measure actual resistance might show something but a better method is to look into "voltage drop" testing. These days there are cheaters with IR cameras like a Flir C3 or C2 who can just look at the electrical system with them and suss out bad connections just by the heat signature.
I seriously want one of those C3's but simply can't quite justify the price. Not yet anyway. I have been hearing about "Load Pro" leads making bad connection testing a bit easier and since they are about a tenth of the C3's price, I bought some. They should arrive next week. I'm looking forward to seeing if they are worth fooling with. The YouTube hype says they are.
Good information. But I think that a bit of clarification is in order.

First off, high in-line resistance does not contribute to the tripping of a circuit breaker. Current exceeding the capacity of the circuit breaker does that. The ultimate in high resistance (infinite resistance) would be to unplug the bulbs, right? If you do that, the breaker will obviously not trip.

Resistance that is in-line will limit current flow, but if there is is a path to ground, that would be summed with current going to the bulbs, and could contribute to a circuit breaker tripping. It should be stated that for the headlights, the circuit breaker is located in the headlight switch, and will automatically reset when it cools down. This heat up, trip, cool down, and reset scenario could be cyclic, resulting in headlight flashing.

Bad connections, corrosion or otherwise, result in resistance. At that spot there will be a voltage drop and heat will be developed. The calculation for power, in watts, is current squared times the resistance. Can the heat be enough to melt things? In a headlamp, blower motor, or starter motor circuit; yes.

If there is a path, or partial path to ground, that loss coupled with the draw from the headlights themselves could trip the breaker. There is not a lot of margin in the breaker. The most common cause of tripping breakers are bulbs that draw more current than the original design.

There was a Ford TSB on the issue in 1972 that mentioned an increase in bulb output and commensurate draw. Note the "bulb 1" document. This applies today to a bulb that consumes more power than the original.

The shop manual has the circuit breaker at 12 amps. The Cougar is listed at 18 amps - something that might be an option. But we would need to look to see if the Cougar wire gauge was increased over the Mustang - I don't want to make a recommendation that results in a fire.

If you are looking to keep things original, my recommendations are to:

1. Install headlamps that don't exceed the original bulb wattage. Shop manual lists the 6012 bulb at 40(low) - 50(high) Watts. The TSB calls out C8AB-13007-A.

2. Make sure that all connections are clean. Even if they look clean, take them apart and polish them. Look at the wiring diagram to see where all of the connections are, and clean them all.

If you want headlamps with increased wattage, install an interposing relay design, so that the headlamp switch only needs to energize the relay(s). Make sure though that the power to the bulbs is protected by means of a circuit breaker or fuse, and that the protection does not exceed the capacity of the wire. I think that I've read about a design or two being commercially available, but I have not researched any of them so can't make a recommendation.

Remember, resistance is futile!
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File Type: jpg bulb 1.JPG (105.5 KB, 3 views)
File Type: jpg bulb 2.JPG (118.2 KB, 4 views)

John
67 289 GTA Dec 20 1966 San Jose
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post #13 of 15 (permalink) Old 05-12-2019, 08:24 AM
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I looked at NPD and Virginia Classic Mustang and nobody appears to list the bulb wattage. Bummer.

Doing a generic search, looking at results from several locations including Napa, has all bulbs listed as 50/60 watts, not the original specification of 40/50 watts.

I did some math and with the 40/50 watt bulb, coupled with the tail lights et al, the total draw would be about 8 amps. Going to the 50/60 watt bulbs would change that to 9.5 amps. Both of these are less than the shop manual stated 12 amp rating of the circuit breaker.

I did some reading on circuit breaker degradation but did not come up with anything useful.

John
67 289 GTA Dec 20 1966 San Jose

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post #14 of 15 (permalink) Old 05-12-2019, 01:56 PM
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Swapping to the Cougar headlight switch, where you can, with the higher rated circuit breaker has been a popular band aid fix for many years. And in these days of iffy quality reproduction parts, not a bad idea anyway.

I'm not a guy real big on theory. Finding a bad headlight ground and stopping the circuit breaker from tripping works for me. Especially after about ten such successful repairs. New headlight switches, correcting corrosion at the headlight plugs, and such are also helpful but in my experience have rarely been the actual main cause. All such electrical failures are best approached with an open mind because you never know when you are going to be thrown a curve ball though.

As for the Load Pro's. I don't know. I was talking to another guy who said he had one gathering dust in his toolbox and said he'd sell it to me cheap. So I'm giving it a shot. Remains to be seen if it will gather dust in my box too. I figure at least they might be more convenient at loading circuits for testing than my current rig which is an old foglight and some wires. Which works but is a little gawky and I have to admit, not very professional looking. Hopefully the Load Pro can replace that. And take up less toolbox room. We'll see, I guess.
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post #15 of 15 (permalink) Old 05-12-2019, 02:51 PM
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I can't recommend a relay kit enough. Even if you fix the issue, it will make your headlights brighter and you can then run halogens or even opt for a higher wattage light.

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