LED conversion

[Racer 238]

Doing an LED conversion on my 1978 GMC k15. Have all the bulbs swapped out with the LED ground flasher. Cut the blue wire on front side markers and grounded so they don’t flash with turn signals. The only problem I’m. Running in to is if I dont run an incandescent bulb in the front turn signals the turn signals won’t flash. The led buld seems to be stuck in bright sequence and drowns out any flash. Put the good 1157 back in and they work as they should even with LED’s in the rear turn signals. Do I need a resistor in the front TS wiring? I’ve tried several different brand LED bulbs with the same result. Just will not work with LEDs in the front TS. Any idea what I can try next? Thanks!!

 

[Ricko1966]

Yep front lights are wired funny on squares and you will have issues on front turn signals and markers because they won't always be correct polarity for an LED due to how they ground differently in different functions.I would leave incandescent on front markers and turn signals,but someone one here will have a work around. I know someone sells special bulbs for it.

 

[75gmck25]

I’ve seen other cars where the markers alternate like the squares, so there may be a bulb design that works. However, if the old style 1157 bulb keeps it working, it’s probably the best simple solution.

I wonder how the full replacement LED park light housings keep it working correctly. They cost more than I am willing to spend, but LMC and others sell them.

 

[Jgonick]

if I dont run an incandescent bulb in the front turn signals the turn signals won’t flash. The led buld seems to be stuck in bright sequence and drowns out any flash. Put the good 1157 back in and they work as they should even with LED’s in the rear turn signals.

Just to clarify- do the rear lights work correctly all the time or or only with the incandescent in the front turn signals?

also- just curious- did you change both the turn signal flasher and hazard flasher?- If not, is there any difference when you use the hazard lights?-or do they act the same.

 

[TotalyHucked]

I've got all LEDs in my '85 and they did the same thing, wouldn't flash at all even with the "LED flasher". I left the LED flasher in the truck and wired in some 50ohm resisters front and rear to get them to work. The little peanut bulbs in the side markers don't need it, just the main signals. So I have four 50ohm resistors in the truck.

 

[PrairieDrifter]

They've been selling the led replacement housings for the fronts of 70's trucks for quite awhile, so they must have it figured out with the relay on those.

The 80's trucks don't have a front led option only side markers. My 84 works fine with the sidemarker replacement housings.

 

[Jgonick]

I've got all LEDs in my '85 and they did the same thing, wouldn't flash at all even with the "LED flasher"

I've been told that a lot of the electronic flashers don't work correctly for all applications.-I'm not sure why it is hit or miss. There is also the polarity issue with the electronic flashers.

This one is known to work well with squarebodies- LINK-United Pacific 90652 LED Flasher w/Polarity Reversing Adapter, Easy Plug-In Design, 12V DC System, 20amp

In theory- How he fixed the side markers should be fine- everything should work (except side markers flashing)

 

[Tonimus]

There's two issues regarding turn signals. Different polarities and the flasher. Look for LED bulbs that say "non-polarity". These have a rectifier in them so they work with either polarity. Flashers have been covered already.

 

[Racer 238]

Just to clarify- do the rear lights work correctly all the time or or only with the incandescent in the front turn signals?

also- just curious- did you change both the turn signal flasher and hazard flasher?- If not, is there any difference when you use the hazard lights?-or do they act the same.

The rear LEDs only work correctly when the incadescents are in the front. I did not change over the hazard flasher to led but it acts the same way as the turn signal. Maybe I should swap that out.

 

[Old Guy Bill]

The LED front sidemarker light fixtures from LMC work, flashing properly when connected properly.

https://www.lmctruck.com/lighting/sidemarker/cc-led-sidemarkers

 

[Jgonick]

The rear LEDs only work correctly when the incadescents are in the front. I did not change over the hazard flasher to led but it acts the same way as the turn signal. Maybe I should swap that out.

You will need to eventually swap the hazard flasher out. But it seems to me the LED flasher you have isn't working properly. You probably need to either add some resistors like @TotalyHucked mentioned or find a electronic flasher that works properly. This flasher has to be grounded but it seems to be a popular one that is known to work with your type of setup. LINK-United Pacific 90652 LED Flasher w/Polarity Reversing Adapter

I like this video (even though it is a jeep it still applies-) LINK-Video