Led tail lights

Nonturbo said:

However based on my personal experience if you have LED front tun signals or an LED third brake light you will need load resistors to prevent hyper flash or upsetting your PCM.

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The PCM has absolutely nothing to do with the taillights/brake lights.

csp said:

The PCM has absolutely nothing to do with the taillights/brake lights.

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An automatic transmission will have problems due to power backfeeding making the truck think the brakes are being pressed when they aren't. Then the trans will never allow the torque converter to completely lock causing it to drive poorly. I hope that clears this up.

How is power going to backfeed? It isn't like a bad ground.

great lights.. I wanna set

or a write up with pics an instructions..

csp said:

How is power going to backfeed? It isn't like a bad ground.

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I don't know how it's works exactly but I'm not the only person to encounter this problem. The led running lights don't really burn any power so some power gets sent up to the third brake light (I do not know how) and if there is a hale gon bulb it burns the little bit that gets sent to it and there's no problem. But if it's a led the bower makes it through and tells the truck the brakes are on all the time. Again I don't know how or why but that's how it was explained to me when I ran into this problem and a load resistor on the third brake light solved the Problem so I'm inclined to believe it's true

Not my style but A for effort.

As for the LEDs giving the PCM fits, no. but it will give the RAMS module fit because it thinks bulbs are out

PCM would control auto tranny TC based on BPP input, not completing a circuit through taillights...

BigRed02 said:

PCM would control auto tranny TC based on BPP input, not completing a circuit through taillights...

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Here's what I was told. "You need the load equalizer/ballast resistors, since the PCM uses the ground returning through the bulb filament when the brake is off to confirm the brake light circuit is complete" that's from someone who knows far more about it than me and he has leds in his tail lights as well.

That's just incorrect. The only thing that goes through the filament is power when the lights are activated. There isn't a ground return through the filaments.

This is completely unrelated but it shows how the leds have an odd effect. With front and rear turn signal leds, and an led third brake light with no load resistor in it, pressing the brake illuminates the front marker leds. And if LEDs are in the gauge cluster lights they also illuminate when the brake is pressed. I know very little about how these old trucks wiring diagram works I just know that the LEDs have odd effects and were causing some kind of confusion with my transmission. Maybe it's just mine and one other guys truck that does this... That's about all o have to say about it.

Where can I get a set? or are they custom? If they are do you have any pictures of the process?

Konman350 said:

Where can I get a set? or are they custom? If they are do you have any pictures of the process?

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I am curious also!

csp said:

That's just incorrect. The only thing that goes through the filament is power when the lights are activated. There isn't a ground return through the filaments.

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Don't know why, but at least the obs truck do feed a slight amount of power through the circuit even with the brakes off.
When I was swapping bed I went bed less for a few days and had thrown on some led tail lights. Just sitting there, they would be on faintly. Like only two leds were being powered. (Which is the tail light function)
Once I added the incandescent side markers and headache rack lights, it quit doing it.
I don't quite remember doing anything else that would "fix it," just adding in those other lights.

And what about all the people that has trans issues when adding leds all around?
Why won't cruise work if the center mount brake light is out?

Cruise in/op should point to that BPP input. It's odd that the signal is there even when switch is open, but they all have a redundant contact. The OBS could have theirs somehow in the lamp circuit. Sounds like there is a resistor of someone in parallel.....

The typical problem is, with an inop center stop light or LED bed lights, cruise and automatic TC function is normal until you hit the turn signal. THEN, becuase of the different load and/or the open circuit at the center stop light, somehow the turn signal sends an eddy current through the brake pedal switch circuit (since the brakes and signals share the circuitry back at the bed), which is then picked up by the PCM, which disengages the cruise, and unlocks the TC on automatic trucks. I've been meaning to post the EVTM pages for these circuits, to allow someone with good puzzle-solving skills to noodle out exactly what happens when in these situations. Suffice it to say, it is a real phenomenon with our trucks, and if they had just ditched that cold-war-era notion of sharing the brake light and turn signal circuits in the same bulb filament and used separate orange turn signals, this would probably be a complete non-issue.

Agreed, the Super Dutys use a separate circuit for the PCM input, and a relay for the lighting circuit....