Question: Old School Flasher


May 23, 2010
Okay... back in "the day" you could take a 3 prong (turn-signal) flasher, and wire it in a manner that would give you an alternating flasher- if done correctly.

The new ones nowadays won't let you do that. I noticed this evening 4 and 5 position flashers too.

Surely- without spending $30 on an alternating flasher- there is a way to get one of these 4 or 5 pinned flashing units to alternate.

Does anybody have a schematic to do this? This is driving me nuts.




Jun 13, 2010
you need a type 537 flasher. That is a three prong design.

A standard flasher will not alternate. period. no matter if its 2 or 4 prong.

most auto stores carry a 537, like NAPA or Carquest, etc



May 21, 2010
USA Nashville Tennessee
The "old school flashers" were thermal flashers with metal contacts. Most of the newer flashers are electronic flashers with a minimum draw for alternating the side marker lights with the turn signals. If it does flash alternatively, the flash cycle will not be 50/50.

The 537 flashers and some of the "old" school bus flashers still have an amp limit as to the number of lamps they will flash, depending upon current draw. Dietz marketed a flasher used on ambulances and fire apparatus that had a larger capacity, but it was still a thermal flasher, with a particularly loud "click, click". Some of the original Unitrol headlight flashers, which were essentially a 537 rigged through relays, might be used were you need an old school flasher.

The best path IMO is to change over to old electronic flashers, like the Code 3 710 or 711, when you need to update the lights.

The Code 3 flashers are nice because they are flat and have screw terminals. I have even used one as a relay for fog lights.

One of the ELB members in New York bought some old Whelen headlight and taillight flashers I had to modify his lightbar. He said they Worked fine and they probably won't burn out like the thermal flashers.

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