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I have two new flashers purchased from Amazon and when I am at a light the rate of flash will slow down to the point of stopping. If I go into neutral or pull away the flasher starts up again. Are there better quality flashers out there that I can buy?
I also see that there are flashers with a ground wire pig tail.... are these better and will they work?

1969 Mach 1
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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I feel like you are focusing on the symptom and not the root cause. (Maybe.) Do you have a voltmeter? If not, might want to use one and see if your alternator output isn't very weak at idle. Stock meters in the dash aren't good enough to really inform you of such an issue.
 

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That's interesting, that's a new on on me? I'm still living in the past so when you say electronic flasher I'm sure if that means the old style with the circuit breaker inside or something new I know nothing about. The original ones need a certain amount of amperage to trip the circuit breaker inside. As soon as it cools it resets and process starts all over again.If either one of the front or rear bulbs were to burnout on one the same side there might not be enough amperage to trip the circuit breaker. That's normally what goes wrong, either that or the flasher just wears out.

In your case its a little different. I have to assume the same thing is going on as far as the amperage flow. There is not enough amperage flowing through the circuit to cause the flasher to break the connection. The wrong bulbs could cause low amperage in the circuit. A bad ground could do the same and of course bad flashers but any off those would cause the problem all of the time.

Your changing the rpm of the engine when you kick it into neutral or start driving. That would cause the alternator to spin faster and charge more, raising the voltage. I That extra voltage (pressure) causes more amperage to flow which might explain why the flasher starts working. The alternator should put out 14.2V at idle but some alternators just do not charge well at idle, sometimes its a bad diode in them or the idle speed is too low. If you put one of those large GT-350 alternator pulleys on there that would slow the alternator down and it might not start charging until the rpms pick up.That does not explain why it does not flash off of just the 12.6V battery voltage? It should still flash off of just the battery with the engine off.

You need to think about what has changed from original, maybe the type of bulbs or the type of flasher. There should be an amperage rating for the bulbs and the flasher. A bad ground, but I think (?) that would only effect one side of the car. Check to see if your brake lights are nice and bright that would tell you if you have a ground issue at the rear.

Like I repeatedly say you "need" a voltmeter for any electrical diagnosing or your are guessing. You need to know if the correct voltage is there before you start doing anything else.

If you have bought some kind of exotic flasher I'm not aware replace it with a good old fashioned two-prong or three prong flasher. I forget which one of the two they use? We used "Ideal" brand flashers for 30-year's at work so I know they are good or at least they use to be good. It was pretty common for the OEM flashers to die probably around ten-year's old. That's an old school flasher with a moving contact inside. Now that I'm thinking about it I have never replaced a flasher in a late model car less then 20-year's old. They might not even have them. They probably use transistors inside a body control module to do the switching on and off.

I thought of something else. They use to sell regular replacement flashers and heavy duty replacement. Sometimes the heavy duty ones would not work on vehicle with just one turn signal bulb front and back. They might have been designed to be used with flashing sidelights too or maybe for towing a trailer with turn signals. The flasher has to be engineered to flash at a certain rate based on the amperage flowing in the circuit. Two bulbs would not pull enough amperage to make a heavy duty one flash and a regular flasher might flash too fast on a car with extra side marker flashers. The extra amperage causes the flasher to heat up faster which opens and closes the circuit faster.
 

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If you are not using LED bulbs you need to go back to the old style flasher. LED flashers are designed to be used with LED bulbs and will not work properly with regular bulbs.
 

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I think any flasher out of a modern vehicle utilizing incandescent bulbs is electronic in nature these days. My wife's newer ride, a 2001 Isuzu Vehicross, started flashing as soon as the signal switch was activated and I wanted this feature in my 86 mustang. Off to the auto parts I went and I bought a two prong flasher for something in the 2000's. Worked like a charm and flashed the same speed regardless of voltage. Newer flashers for LED lights are made for LED lights and not incandescent bulbs. I have no experience with LED lights so take this with a grain of salt.
While the 86 is long gone (wish I still had it) my 67 still has the original flashers installed and they work great.
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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They aren't actually "LED" flashers, they are electronic flashers that when activated will cycle at a predetermined speed. Within their load limits, it doesn't matter what sort of lights or other devices you have on them, they just cycles the power on and off. What does affect them is unusually low or high voltage and bad connections. Hence....
 
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What's going on is this. The flasher has a bimetallic strip that has a specific resistance. As current goes through the strip, it heats up, curls and opens the circuit. As the strip cools it straightens out, makes contact and repeats the action. For a specific amount of current going through the switch is going to produce a certain amount of heat. The more current, the more heat and the faster the blinker works and less current, the less heat and the slower the flasher works. 2 things that effect the amount of current. Amount of circuit resistance and amount of voltage. Or a combination of both.

You could have poor contacts on the bulbs or connections. Poor connection reduces current and makes the blinkers slower. As you rev the engine, you produce more voltage which will cause more heat in the flasher. You could have a combination of the two going on. First I'd suggest cleaning all the sockets and bulbs first. You could also have the wrong bulbs, lower wattage means more resistance and slower operation. Check your battery connections too. Last thing check your idle speed, may be too low.
 

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This might not be your problem, but I had the same issue with my 67 Mustang. Flashers slowed way down when the vehicle was idling at a red light or stop sign. Then one morning it seemingly cranked fine, but would not start. Took the battery out of my truck, put it in the Mustang and it was an instant cure: started instantly, flashers work fine under all conditions. As best as I can remember, the Mustang battery tested about 12.2 volts, but didn't have the "oomph" to crank the starter and run the ignition system at the same time.

I agree with Vintage Ford Guy, you need a voltmeter to diagnose electrical problems on a vehicle.
 

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The ORIGINAL flasher is electronic. Electricity goes in one side, out the other, and the current heats up a bi-metal element that makes and breaks a circuit. What you want is a SOLID-STATE flasher that relies not on series current flow, but a very small amount of current produced by a parallel connection (hence the ground wire), to power an integrated circuit to make and break the circuit. The result will be a constant rate of switching regardless of input voltage variations or line loads.
 

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Discussion Starter #13
Wow.... thanks for all the help and suggestions.
I do have a meter and will test the voltage at idle and under load.
The entire car is now LED except for headlights and hood mounted turn indicators.
I have removed and cleaned all the ground points I could find.
Have a new battery and replaced the regulator with an electronic one which solved 90% of my problems. The Alternator gauge was bouncing back and forth like it had a mind of its own.
I now see that there are two prong flashers on the market which have an adjustable pot to change the rate of flash...... Interesting and will get one to test out.
 

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Huskinhano; almost right. It's rather unintuitive. When the bimetalic strip is heated from a low current (like a single bulb) it doesn't deflect as far because of the lower heat generated. This allows it to cool off faster (less heat/lower deflection/shorter distance) thus making the blink speed increase when you have an out bulb.

I also agree that the alternator output is dropping in the OP's situation. Hopefully it is not a bad diode and only a loose belt.
 

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Huskinhano; almost right. It's rather unintuitive. When the bimetalic strip is heated from a low current (like a single bulb) it doesn't deflect as far because of the lower heat generated. This allows it to cool off faster (less heat/lower deflection/shorter distance) thus making the blink speed increase when you have an out bulb.

I also agree that the alternator output is dropping in the OP's situation. Hopefully it is not a bad diode and only a loose belt.
No, Tom is correct. The more load the faster the flasher trips and resets. When you have a bulb that blows and the filament drops down and shorts the bulb it will add load and flash fast. If the bulb blows and remains an open circuit, it won't flash at all. If you look at your old owners manual the sign that you have a blown bulb is that the indicator light will come on and stay on without blinking.
 

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I've never seen a filament "short" a bulb. Seen plenty where the remains of the filament was lying inside the globe on the glass and nowhere near the contacts and so making it an "open". Every of those flashed fast. Never really put a lot of thought into why.
 

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Hi there! I installed rear tail lamp LEDs for my 68’. I used Vintage LED from Gary and also the two flasher modules. There is one for the turn signals and one for the hazard lights. I tested the flashers with regular bulbs and they worked fine. Then put in my tail lights. I now have LED rear and regular front. This is the part x 2 that I have. Did not source it from CJ but this is the same one. Hooked up the wire and fork to ground by loosening the nearest bolts and making them snug over the U terminal. No problems since. You may have another issue but if you need an alternative part and you don’t have these here it is:

 

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The filament is a short by nature, but has a controlled resistance that is temperature related (resistance goes up with temperature) and also related to how much light it produces when energized. The lights are in parallel, so when one opens, it does not affect the other operationally. If the bulb was truly a short as a failure mode, it would pop the fuse.
 

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I had a similar issue and looked at, or replaced bulbs and some wiring and light fixtures. Still had the problem. Went to auto parts store and got a flasher with lower resistance. That fixed it. Could be that the resistance on yours is incorrect. Is the correct ohms specified in the shop manual - anyone know?
 
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