LEDs for 97-98 tail/brake lights

M

markup97

Lost in Translation
Ok, so the 97-98 MKVIII can tell if you have a light out and report back to you. This is called the CAN-BUS system, correct? The 94 back-half I have grafted to my 97 front half works great with regular old 3157/3457 bulbs. As soon as I install LEDs in the brake/turn/park position, the 'Check brake light', 'Check Rear Turn' messages illuminate and the bulbs flash fast, as though a bulb were out (even with the LEDs working properly.
I know this is a proper function with standard LED bulbs installed as CAN-BUS is not getting proper amperage readings. Now, when I install the LED bulbs supposedly meant (and marked for CAN-BUS systems) for this system, I STILL get those same results.
What LED bulbs work, or will I have to wire in a 100ohm resistor no matter what LED bulb I go with?
 
tixer

tixer

Lincoln Evangelist
I'm on board with the resistors as well. I don't know what system the car uses to communicate the information, but it's obviously expecting the current draw of an incandescent bulb.. As far as I know, the standard solution is to "trick" the system by adding that resistor..

Considering my 1986 Town Car had a similar feature, I strongly suspect that it utilizes a simpler and independent "network." CAN is pretty advanced, by automotive standards. I doubt they'd use it for bulb detection.
 
M

markup97

Lost in Translation
Mike,

You are more than likely correct on CAN being a bit advanced for this year car. I was referring to the nature of the bulb and its' compatibility with the auto system (thinking that the car may also be CAN. It does use a voltage/amperage BUS system; albeit basic, to monitor the lighting).

We use a LOT of CAN-BUS in the aircraft; much smoother and lighter being able to transmit many signals of information over one wire versus a wire for every component. The computer monitoring and transmittal of information has taken a LOT of weight out of the airframe (even though it has added some programming complexity).

Thank you for those who have replied. Looks like a trip to my local Radio Shack (or better electronics supply house) will be in order. I have some future plans that will further reduce the resistance load on the circuit, so resistors will surely be needed to restore the lost 'signal' to the lighting control module!
 
M

markup97

Lost in Translation
Now, my next bout of 'stupid question' with the 100ohm resistor; would I want a 1/8w, 1/4w, or 1/2w unit?
 
driller

driller

El Presidente
Product Description

Two 12v 50w 6RJ up grade resistors with built in Heat Sink, These LED Load Resistors will overcome the problem with warning errors, bulb blown messages and bulbs flashing, that you get when installing standard LED bulbs to your car, bike or truck. They are easy to install, just plugs straight into your exsisting light socket. PLEASE NOTE RESISTORS GET HOT
Click to expand...
It is recommended that they are mounted to a metal surface for heat dissipation.
 
C

chris2523

New member
30w and up is probably sufficient.
the brake/turn filament in a 3157 pulls 27 watts, the running light filament pulls 8.3w.
 
S

steve

With "LOD" Since 1997
The resistors get very hot. I first tried them on my Vette and they melted



Then I changed out the flasher and spliced in LED one, no more hyper flash and no hot resistors.

 
tixer

tixer

Lincoln Evangelist
I'm surprised by how much you had to take apart to get to your flasher.... :D

The maxed out "speed sensitive volume" adjustment makes me smile too, for some reason..
 
S

steve

With "LOD" Since 1997
Yes the flasher was buried in the dash. Well after my mods my vette was very loud, so needed all the volume I could get.

When I get around to it and research it I hope i can do the same mod to my Flex front lights to LED, the tails lights are LED. The flasher looks to be in the fuse box in the engine compartment.
 
M

markup97

Lost in Translation
So, find my flasher unit and swap it out for one of those LED flasher units (that is, if my flasher isn't an integrated part of some control computer).

If it is integrated, I remember seeing a write-up somewhere about someone soldering resistors to their LED bulbs to fool the sensor into thinking the LED bulbs were standard 3156/3157 (3456/3457) bulbs.
 
M

M Darrah

New member
It's a shame there isn't a better way to avoid the message center warning without wasting watts on basically small heaters. These cars are borderline starved for electricity as it is.
 
tixer

tixer

Lincoln Evangelist
I suppose adding a similar resistor only to the circuit that "tests" the lights would do the trick. That's assuming that it tests only at regular intervals, and not "all the time."

Now you guys have me thinking about finally getting a service manual...
 
C

chris2523

New member
in the first gens, you just cut the wires (i think 3?) like you do for the headlights or air ride.
my 93 has LED turn signals front and rear, and an LED flasher.
i do not have load resistors or anything like that, and i do not have message center warnings.
 
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