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Discussion Starter #1
Has anybody attempted this mod for normal LED replacement turn signals on the 124? Is it the same module layout?

https://mx5things.com/2018/04/01/tear-down-bcm-fixing-hyper-flashing-with-leds/

I currently have resistors (had to add at each location) but seems messy. I’m not a fan of the LEDs with built in resistors. The additional loading just seems to defeat one of the purposes.

I’m handy with the soldering iron, but seems like an expensive part to get wrong.
 

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Discussion Starter #3
Ok, so after a bit of a delay, I now have resistor(s) to do this mod to remove the 50w load resistors. But am stuck...how does the BCM come out? There is a clip at the top of the module, but it’s impossible to get a hand up there to remove the clip. Is there a trick?
 

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Discussion Starter #5 (Edited)
BCM Modified successfully

I have finally managed to get rid of the 50W load resistors, and am running regular LED turn signals without built in loads. There are a couple of tricky spots - as @ssh16 says on his blog post, it isn't for everyone.

Link to removing the BCM: http://mazdaman.x10host.com/sm356376/. Remember, if you have a manual transmission, go down to the section marked MT - makes it much easier. I didn't remove the drivers side trim, so it probably would have been a lot easier, as getting to the harness clips would have been easier. You need to remove thos harness clips, to be able to move the wiring loom out of the way to get to the clip holding the BCM in place.

Helpful link to the location of the resistor that needs changing: https://mx5things.com/2018/04/01/tear-down-bcm-fixing-hyper-flashing-with-leds/

The Surface Mount resistor is tiny. Did I say tiny? I meant miniscule: it is 1.6mm (0.063") long. You will need some fine eyesight and a fine tipped soldering iron. I don't have the former, at my age, but have the latter. A good magnifying glass really helped.

I soldered on two wires after desoldering the resistor. Extra-flexible silicone insulated tinned-copper 30awg. https://www.amazon.com/gp/product/B01KQ2JNLI/ and soldered a 1/3W resistor to the end of that, instead of trying to solder an SMT component back.

The resistor(s) were then insulated then double sided 3M foam tape used to hold it onto the front connector on the board.

There's another reason to use the leads: if I need to change the resistor, then it's a lot easier. And in fact, I did.

Initially, I used a 4.7kohm resistor, as recommended. I suspected this was way too low, but gave it a try. two incandescent bulbs plus an incandescent side repeater draws about 5 amps. The original resistor is 1.3kohms. The LEDs I have consume 220mA each (front and rear) and 20mA on the side repeater, for a total of 460mA, about one tenth of what the incandescents draw.

With a 4.7kohm resistor, plus load resistors simulating incandescents, the turn signals don't work, or the emergency flashers. They flash on once then turn off. This is probably because it sees a short circuit (too much current detected). Removed the load resistors from the rear lights (I needed a load resistor both front and rear, for a total of 4 resistors). Hazards now work, and turn signals work. Removed a load resistor from the front right: hazards work but right turn still gives hyperflash.

Doing the math (above) I went with a total of 13kohms (10k + 3k in series), as shown in the images. Removed all the 50W load resistors, and both turn signals work, and hazard lights work. Removed a turn signal bulb from a socket, and the hyperflash started, as expected and desired.

Because of the low current draw, the current sense circuit - according to the data sheet - probably around 100uA, instead of 1mA with the standard resistor - I was concerned about it showing an 'open' circuit leakage current fault (if that feature was utilized), but that threshold at the very low end is 4uA, so no problems there.

Problem areas: removing the BCM (should have removed the drivers side trim); desoldering the SMT resistor; soldering two wires on. The rest is cake (but I had a whole bunch of resistors, a quality temperature-controlled fine tipped soldering iron).

So, final thought(s): why not use resistors? Why use 4 resistors (2 each side) instead of 2? Why not use bulbs with built in resistors/loading?

The resistors are an ugly hack, get hot, and defeat one of the purposes of using LEDs (Lower power consumption). The LEDs I selected have a very low power consumption for the light they put out (260lm for 220mA); remember, this is an amber bulb behind an amber lens. Bulbs with built in resistors run the risk of transferring the heat generated to the 'wrong' part of the bulb: I.e. the bulb housing. I'd not recommend using such bulbs, unless from a reputable source, properly designed for an incandescent replacement.
 

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Discussion Starter #6
Update: I had to change out the resistor from 13k to 15k.

With the car off, the signals worked fine. With the car on (cold morning) the left would hyperflash, but the right was OK. The voltage on the system was marginally higher (or lower, I never really got to the bottom of that). The left side was drawing marginally less current than the right side, so was on the hairy threshold.

I removed the drivers side trim, this time (only takes a couple of minutes). It helps a bit, but it's still really tight to get your hand on the connectors.

Anyone doing this mod would need to check the loading on their bulbs to see what resistor they would need.
 
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SJWhiteley
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