(Feeler) LED Turn Signal Solution for Tacomas with DRLs - WORK IN PROGRESS

The turn signal and hazard flasher on most vehicles' blink rate is determined by the current draw of the circuit downstream from the flasher. This implements the feature that causes the flasher to "hyperblink" when a bulb is burned out or missing. Unfortunately, this causes issues when installing LED turn signal bulbs because of their much lower current draw (~250mA vs. 2.25A incandescent).

Tacomas without DRLs can buy aftermarket flasher relays tuned for the lower current draw of the bulbs to fix this problem. As for Tacomas with DRLs, two solutions currently exist:

Option 1: Open up the flasher box (which is in the dash near the steering column) and grind down the shunt resistors in that box until box is tuned for the new current draw. Discussed here.

• Pros: Requires no wiring modifications, reduces power draw (one of the primary reasons for using LED bulbs)
• Cons: Irreversible, difficult to get tuned just right, requires trial and error, and if you grind too much of the shunt off then you're stuck buying a new flasher

Option 2: Large resistors in parallel with new bulbs. Discussed all over.

• Pros: Reversible, easy to install, no tuning or trial and error required
• Cons: Does not reduce power draw, generates lots of heat from resistors

So I am attempting to create a solution that eliminates some of the worst cons of both of these approaches. This thread exists to document my experience, I do not have a usable product yet.

My design goals are to reduce power consumption, eliminate hyperblink, and have the solution be plug-n-play (no tuning required).

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This is the first candidate schematic for the design. The important part is that it requires no external constant source of 12V power; it powers the light and adjusts the blink frequency using only the power provided to it by the (hyperblinking) turn signal wire. So with this design, the indicator in the cab would still hyperblink, but the bulbs on either end would blink at the correct rate.



The the box labeled "Turn Signal Circuit" contains the parts and wiring already on your truck. Everything else would be contained in a small module that would be wired inline with the bulb.

I simulated the hyperblink input (about 3.3Hz) and then measured the simulated output of that circuit.



Top is the module output, bottom shows the input from the truck.

So share your thoughts about this, would it be useful to you? Do you think the other solutions are better? Does it suck? Let me know.