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DIY: Turn signal flasher for LED bulbs

Some of us have been waiting a long time for a company to release a replacement turn signal flasher that will accommodate LEDs. I got tired of waiting for someone to put one on the market so I modded my stock one. This post is to share what I did.


My Tundra came with DRLs activated. Since I personally do not like DRLs, the first order of business was to deactivate them by replacing the 81980-0C010 'with DRLs' turn signal flasher with a 81980-0C020 'no DRLs' turn signal flasher. Having done this, I ended up with the old 81980-0C010 that I could use for experimentation.


The Tundra turn signal flasher uses resistance loops as a reference in deciding whether it thinks a bulb is burned-out or not. The problem with LED turn signal bulbs is that they alter the resistance perceived by the turn signal flasher enough so that it causes the turn signals to hyper-flash to tell the driver that there is a bulb burned out. In theory, altering the reference resistance value that the turn signal flasher sees could allow LED bulbs to be run without the hyper-flashing.


Up till now the only solution I've seen for hyper-flashing LED turn signal bulbs on our trucks has been to add load-resistors in series with the bulbs. My own opinion is that this is a cheap and dirty way of patching LEDs to work properly as turn signals, so I have never considered that method. Many other cars and trucks have aftermarket LED turn signal flashers available for them, why not us?


So that brings us to our leftover 81980-0C010 flasher. The first thing that was needed to be done was to determine what the resistance range on the reference circuit was that would allow LED bulbs to function normally. I desoldered and removed the lefthand side resistance loop and replaced it with two short solid copper 16 gauge wires with copper spring clips soldered on them. With this setup, I could attach a large 500 milliohm rheostat to the clips while the flasher circuit board was connected to the plug in the truck.
(Pic #1)

With my LED turn signal bulbs installed front and back, I would slowly alter the reference resistance using the rheostat until the turn signals malfunctioned. Right at that point, I would unclip the rheostat and measure its resistance value with a digital VOM and record the results. I did about 12 runs for both the lowest and highest allowable resistance. With the LED turn signals operating properly, dialing the resistance down too low would cause hyper flashing. When the resistance was dialed too high, the flashers simply stopped. The approximate average resistance range for my LED bulbs to operate normally was 65-250 milliohms.


Next it was necessary to find the largest power resistors (in wattage) that I could get that were of a usable resistance value and would also fit inside the Tundra flasher's housing. This wasn't easy; I went through at least 4 different resistors before I found the best compromise. The ones I used are Vishay wirewounds / 11 watt / 100 milliohms. Mouser part number 71-RW68VR10. I would have liked to have used higher wattage resistors, but they wouldn't fit in the housing.


One school of thought I encountered online while researching this project was to simply grind down the resistance loops on a flasher being modified until the resistance changed enough to allow LEDs to work. The article showed resistance loops, still installed in the circuit board, being ground with a dremel tool until the cross-section was narrowed down considerably from its original size. I didn't like this idea personally because (1) it would spread conductive dust all over the surface of the flasher board and there would be the possibility that not all of it would blow off using a blower nozzle on a air compressor, and (2) there is a name sometimes used for a thin resistance wire carrying current...it's called a filament.


At this point I went and purchased another 81980-0C020 'no-DRL' flasher to mod into a finished unit. On each of the two resistors I used, heat shrink tubing was applied on both the resistor bodies and the long folded leads for a little extra protection against chafing/shorting. The stock resistance loops were desoldered from the flasher circuit board and the power resistors were soldered in their place. The board and resistors fit inside the flasher housing ok.
(Pics 2-7)


I've now been driving my Tundra with the modded turn signal flasher installed for about four months. I have v-leds 3157ck bulbs up front and v-leds 3157's in the back. The turn signals work properly with no problems.


I will mention a couple issues that I know of:
First, if I wanted to go back to incandescent bulbs, I don't know how well the resistors I used could handle the additional current. The flasher circuit is, after all, an intermittent-on instead of constant-on, so heat generation might not be a problem, but then again maybe it would. I would be leery of using this modded flasher with incandescents.
Second, there is the possibility that a different make/model of LED 3157 bulb could skew the sensed resistance enough so that the values of the resistors I used wouldn't be sufficient. I have no way of knowing if a different 3157 LED bulb would be enough to cause problems or not since I only used the set I have. As it is, v-leds has already discontinued the bulbs I used for this project and are what I have installed on my own truck.
Just wanted to mention those points in case anyone here feels inclined to build one of these for themselves.
 

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Excellent write-up.
The current draw of LED lamps is almost insignificant compared to incandescents. Was it necessary to use such high-wattage resistors, or were you just being cautious?

Steve
 

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Excellent write-up.
The current draw of LED lamps is almost insignificant compared to incandescents. Was it necessary to use such high-wattage resistors, or were you just being cautious?
Thank you.

When I set up the testing rig, I did put my VOM in series between one of the flasher board's copper clips and one of the rheostat legs to see what the current passing through was. Unfortunately, I can't remember the numbers that I got. The 11 watt resistors are based on what I felt at the time was the lower end of acceptable safe wattage rating with the current loads the v-leds bulbs make.
 

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I like this mod.
I put a switch in my DRL circuit so they could be turned off after I found the heat from the bulbs was turning the plastic bulb sockets brown. Now I can put in LEDs and turn them back on without concern for long-term heat damage.
Thanks.

Steve
 

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DIY: Turn signal flasher for LED bulbs

"there is the possibility that a different make/model of LED 3157 bulb could skew the sensed resistance enough so that the values of the resistors I used wouldn't be sufficient."
Sure enough, the newer LED turn signal bulb combination I changed to earlier this spring caused my v1.0 turn signal flasher relay to malfunction. I got hyperflashing, but strangely, only under one condition: Engine running + headlights on.
With the truck in any other state besides that one, the v1.0 relay worked.

The result was my building of a v2.0 model. This one used 14-watt 200-milliohm power resistors (Mouser Part# 66-W24R200JBLF). In the truck, this relay worked fine with the new LED bulbs combination. Pictures attached of v2.0 relay. (Yes, it fit in the relay housing just fine)

Ironically, I changed to a yet newer turn signal bulb combination very recently that required me going back to the v1.0 relay since it wouldn't work with the v2.0 relay (Too much resistance; flasher wouldn't blink at all).
I'm currently running Vleds '3157_21_A_CK' bulbs in front and '3157_21_R' bulbs in back through the v1.0 relay with no problems.

EDIT: The 3157_21_R bulbs I am using for the rear turn signal bulbs are RED. This is because I am running Hella tail light assemblies, not stock ones. In a stock housing, an amber 3157_21_A bulb would be the one to use.
 

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Awesome write-up. I ordered both sets of resistors to see what works best for me. I have Retro solutions ck 3157 flashbacks and some 3157 turn signals rear
 

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OK, I bought some front LED's for mt 2011 Tundra from AutoZone that kind of resemble Retro solutions ck 3157 and as soon as I turned my key on it popped the 15 amp fuse. I pulled the bulb and reversed it in the socket with the same results. Returned them and put the standard bulb back in and good to go. Now this evening I head to the store and have no tail lights. Brake & turn OK in the rear just no taillights. Hopefully I have another blown fuse, will have a look tomorrow in the day.

Is there a special type of LED I need for my Tundra?
 

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I know this is an old thread, but I recently went through both iterations on my 2016. With the .2ohm resistors, I get normal flash when the headlights are off and hyperflash when they're on. I have a feeling it's due to the switchback front LED's drawing slightly different amounts of current when they're amber vs. white.

I just ordered some 10W .22 ohm (71-CP0010R2200JE14) and 15W .27 ohm (588-TUW15JR27E) resistors. Hopefully one those hits the sweet spot.
 

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Let me know what you come up with I have the V-LEDS and have the same problem I bought the kit with the resistor that says it will not hyper flash it does not as long as head lights are off
 
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