A relay with a two prong flasher

[JohnMarcson]

One way to make an alternating flasher is with a relay and a two prong flasher. I know there are other ways, but I had a specific question about how to alternate a two prong flasher and I figured I would share my fix this way.

Really, just buy an alternating flasher. They aren't expensive and the relay and thermal flasher together is a recipe for failure. But....if you want to try it, here is a way.

Hook up one lamp to the thermal flasher, then wire the thermal flasher output to that light to the trigger of your relay. Hook a second light to the normally closed (powered by default) side of the relay, and when the first light is flashes it will open (turn off) the normally closed (on) side and the light will turn off opposite of the light on the thermal flasher. Now you have the clicking of a thermal flasher and the clicking of a relay. Harmony?

 

[shues]

Dunbar-Nunn produced something that I had originally thought was very similar, the Unitrol 131:

You are both partially correct. The short can 537 pictured on the Gall's unit really wasn't suitable for headlight flashing. It would sort of do OK for a few minutes and then get lop-sided. It did a little better on the lower wattage Par 36's and 46's but not much. It would drive some 1156 bulbs in lollypop turn signal fixtures pretty well. (They used to be the best we could do for grille lights in some cases.)


However, the gold standard prior to electro-mechanical and later electronic flashers was the long can heavy duty version of the 537. It was about 3" long and maintained a steady alternating flash rate. We used them on quad headlight police cars all the time with no problems. The old Dunbar-Nunn Unitrol Model 131 headlight flasher kit came with the long can HD 537 as standard. It also used a relay and could be controlled with a SPST switch. It handled all the switching needed to deal with headlights on, etc. It even had a high beam sensor that disabled the wig-wags all together if the high beams were engaged. Here's a 131 with the long can 537:


View attachment 183290


BTW, there are two of them up on Ebay at the moment, both priced less than $30 which is what we paid for them in the 1970's.

It wasn't until I got my hands on one that I realized the relay is there for function control, not for inverting the state of the two-prong flasher's output.

 

[JohnMarcson]

Dunbar-Nunn produced something that I had originally thought was very similar, the Unitrol 131:



It wasn't until I got my hands on one that I realized the relay is there for function control, not for inverting the state of the two-prong flasher's output.

I don't know of any commercial flashers that use this cheat, there may have been some, I don't know of any. However most relay flashers simply open and close a relay or relays with a simple set of electronics replacing the thermal flasher. You really just need a "pacemaker" and the relay can run two lights if it has a both a normally open and a normally closed. At that point triggering the relay turns one on and the other off, removing trigger power reverses it. If your flasher doesn't require a load to function, you can just use it to open and close the relay and not connect any lights to the flasher directly.