OK I just discovered something I didn't appreciate previously. The 1967-older cars (all of them, A-body, full size, and Toro) do not have any fuses in the turn signal circuit. The purple power wire that feeds the flasher module is connected directly to the hot wire coming from the ignition switch. This was done because the original mechanical flasher module is actually a self-resetting circuit breaker. If there's a short anywhere in the turn signal circuit, the bimetallic strip in the flasher heats up and opens the circuit. Fire avoided.

Here's the problem. If you replace the OEM-style mechanical flasher module with an electronic one (such as when you replace the turn signal lamps with LEDs), you lose this circuit breaker function. I'm guessing that a dead short on the output side of an electronic flasher module will just fry the semiconductors inside the module, but I don't know that for sure. It would be prudent to add an inline fuse to that circuit if you ever change to an electronic flasher, preferably in the purple wire that feeds power to the flasher.

And this is another example of how "upgrades" to newer technologies don't always have the same level of engineering that the factory incorporated.

 

Thanks for sharing your discovery, Joe.

 

Cheesh..more notes to self.

 

I think the new electronic flashers are nothing more that a relay with a internal timer. Turn on the turn signals, the internal timer opens/closes the relay contacts to simulate the function of the bimetallic coil.

If that is in fact the way the new flashers work, I wonder if they designed them with current limiting protection? If not, someone will probably need this:

 

Yes, but I don't know if that relay is mechanical or solid state. Frankly, it could be either, depending on the manufacturer. Solid state relays are probably less expensive than mechanical today, especially if you already have a circuit board in the unit. In any case, unless there's current limiting as you point out, this is a potential problem.

Edit: OK, this one definitely uses a mechanical relay.

 

I like mechanical relays. I need my click clack noise to remind me it's on sometimes.

I enjoy appreciating hidden engineering when I figure it out. Good engineering is simple. Most people with engineering degrees don't do simple. I solved a problem recently with two engineers trying big complicated solutions by determining that it wasn't even necessary to do what they were trying so hard to do.

 

Amen. There's a lot of brute force over-engineering because most people can't see the simple, elegant solution. I'm kind of impressed with the fact that you can use the turn signal flasher as a self-resetting circuit breaker, actually. You probably save a couple of cents on every car by not using an additional fuse.

 

Pretty sure that’s the same flasher I used in my car. It definitely has the mechanical contacts (more than anything just to provide the clicking sound) and a timer to control the relay coil. The cycle time is rock solid, during my dash harness build I tested things with everything from a 194, the factory 1157 bulbs, and finally the LED.

I have one other electronic flasher that I bought but didn’t use because it required a ground wire to be permanently connected. I have a huge 40 amp power supply in the garage left over from my CB radio hobby. In the pursuit of knowledge and the presence of a Y chromosome (men like carange!!) I use the power supply and my Snap On battery tester to put a slowly increasing load on it until it either trips the internal breaker, or burns up

 

This is the electronic turn signal flasher I originally bought but didn’t use

Made by United Pacific

Since it says right on the case input must be fused, it appears this particular model has no current limiting ability.

 

The 1968-up cars are fused from the factory. It's the 67-older cars that are the problem.

 

So, I guess there is no need for destructive testing.

I guess it would cost too much to include current limiting into the design of the flasher. Kinda inexcusable in my opinion. If Joe hadn’t mentioned it in his PSA, it probably never would have occurred to me. Not everyone has a wiring diagram, and in all reality even less have the ability to read and understand one.

Let’s say someone is trying to figure out why their turn signals don’t work. Most people would start with the simple things, check the bulbs, and replace the flasher. If there is a brake light/turn signal wire grounded, the flasher would open the contacts. Imagine the frustration when the new flasher causes the dash harness or taillight harness to burn up.