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2nd gen tail lights led swap issues

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Old Mar 22, 2015 | 12:18 PM
  #1  
N8ster36's Avatar
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From: Planet Earth
2nd gen tail lights led swap issues

Hey whats up RX7 club. I recently swapped my tail lights with led bulbs. At first i had a problem, brake light out indicator on dash came on,lights were bright all the time. Did some reserch and found out that i needed to install a diode on parking light wire. Did that now they are dim and get bright when i press the brakes (ok) but now the brake light out indicator on dash is still on. ??Whats the deal?? Can it possibly be because the led's take way less voltage than incondesint bulbs? Signal lights flash fast too but all works fine,did not swap out front signal lights with led's yet.
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Old Apr 8, 2015 | 11:42 PM
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From: Glendale, CA
The light out indicator is very likely sensing burnt bulbs by comparing the current draw against a minimum expected. With LED lights it's likely the current draw has fallen below this threshold. You can fix this by adding a parallel load such that in combination with the LEDs the net current draw will be the same as the incandescent light bulbs. If you want to do this read the road map below (I don't recommend this). If it were me I'd modify the fault detection circuit or disable it altogether (remove the bulb from the dash).
I also think the blinkers are behaving the way they are behaving because of the same reason. Often these circuits use electro-mechanical devices utilizing heater elements so less current means less heat therefore the time constants change which manifests as altered blink rate and duty cycle. Find solid state blinker relay (not sure what they are called) that are not load dependent and replace.

Remember, below is with numbers that I made up. Except for the voltage I was just guessing for the light bulb wattage. So this needs to be redone.
I don't know the wattage of the original bulbs but let's say each one was 12W then you'd be drawing 1 Amp (assuming the system voltage is 12V). Let's say each LED bulb is using 0.2 Amps. This leaves a balance of 0.8 Amps. Based on this load balancing resistor is as follows: R=12V divide by 0.8A. This give you 15 Ohms. The next thing to do here is to calculate the Wattage that will need to be dissipated by this resistor. For that go ahead and assume 14V instead and calculate wattage as follows: W=V^2/R which in this case is 14^2/15 which is 13 Watts. I'd select a wire-wound resistor of at least 20 Watts rating here. This is a lot of power so mount it such that heat can escape the resistor (i.e. metal surface on the cars body and not directly touching plastic or fabrics). The other thing here is that you'd need to do this for each bulb.

Last edited by DoubleWishbone; Apr 8, 2015 at 11:55 PM.
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Old Apr 9, 2015 | 01:22 PM
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From: Planet Earth
Thank you for the info

Thank you for taking the time to explain to me. I sorta figured that was what was going on. I do see at Auto Zone thay have a resistors with heatsink that prevents the fast flash issues. Man if i have to do every light its gonna cost a few. I am probably gonna have a friend order them online for way less than half the price. Just simple intake gaskets at the Zone is more than double the price than online. I have no idea how thay stay in business. I would think that thay would be forced to lower their prices.

Thanks again
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Old Apr 10, 2015 | 11:49 AM
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From: Glendale, CA
I found this (see link below).... Since yours is not 3rd gen this mod probably does not apply but I agree with avoiding the balancing resistor approach.

https://www.rx7club.com/3rd-generati...ht-way-943516/

Last edited by DoubleWishbone; Apr 10, 2015 at 12:04 PM.
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Old Apr 12, 2015 | 08:21 AM
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cool thanks

I am just gonna roll with it for now. I did so much to this car allready. Pulsation damper went on it. I had to remove upper intake manifold to fix it what a pain in the ***. Eliminated a bunch of emissions crap. Installed dual exhaust ,got rid of messed up catatatlic converter. Electric pump 5th & 6th port mod,3 core aluminum new radiator with complete cover shroud and electric fan electronic controlled. I know i am forgetting something but i am gonna enjoy it the good weather is finaly here.
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