How do the side marker lights work?
 

From my best reading of the diagrams, they are wired as below. This small diagram only shows one side of the vehicle. The other side of the vehicle should be a near duplicate of it.

But, this method makes no sense. The side marker light is never grounded. Am I missing something pretty important, or what's going on here?

Re: How do the side marker lights work?
 

That circuit is not accurate whatsoever. It just shows you a very generic method of operation but is not specific and how it should be wired.

Re: How do the side marker lights work?
 

It might not be accurate, but it's the best I could come up with from the following link.

http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_frt_light.jpg

Like I said, it doesn't make any sense how it could work, but I don't have anything else to go on.

Can you explain the correct method of wiring it? I'm wiring this truck from scratch.

Re: How do the side marker lights work?
 

Doing some more reading, I'm confident I got it correct. I just don't understand why it works like it does.

It does look though, like I cannot use LED bulbs in a couple of positions here. I haven't thought through it enough to see which ones have to remain incandescent.

My diagram was only intended to be a very simple one that breaks it down to the most basic components for easy understanding. It was not supposed to be accurately depicting the whole front wiring harness.

Re: How do the side marker lights work?
 

It does do a good job of explaining how the side markers blink out of phase with the fronts while being lit when the turn signal is off.

When just the running lights are on, the side marker uses the heavy turn signal filament as the path to ground. The side marker is low enough current that the heavy front turn filament stays dark, cold and low resistance. When the front turn signal goes hot, the 12v balances out the 12v on the side marker and the side marker goes dark while the front bulb is lit.

The front park light filament probably has enough cold resistance that the side marker stays mostly dark when the front turn is blinking while the running lights are off.

Things like this are why bad grounds are always a good suspect when lights aren't working correctly.

Re: How do the side marker lights work?
 

Those wiring diagrams are from the Haynes manual.
The GM wiring diagrams are in my signature and they are year specific...

I'm not sure I'd use LED bulbs in anything other than the backup lamps.
I don't care if the license plate is lit any better than it was originally. Not my boggle if people can't read it when it's lit to original specs.
Tungsten filament bulbs do quite nicely in the other positions. It is possible to have the brake and turn bulbs be too bright.

Re: How do the side marker lights work?
 

my whole truck is now led every spot and love it .

the front fender marker / turn just need a NON-polarity sensitive led bulb is all for it to work correctly . reg parts store ones do NOT work correct in this position .

its not on this site but i have a super write up and tons of pics over on www.ck5.com in this thread . https://ck5.com/forums/threads/l-e-d...lights.335580/

if i get some extra time i could copy and paste and load the pics here and make a thread on this site .

with out seeing pics you can skim my thread and get the best ones as i posted links in all the posts with good stuff or posted the name and style of the good stuff .

Re: How do the side marker lights work?
 

Not to hijack the thread, but in regards to side marker lights, is there supposed to be a gasket behind the marker light? My 79 PU has no gaskets for the side marker lights, like you would have for tail lights or front signal lights.

Re: How do the side marker lights work?
 

Do you have the "winking" side markers, or the steady variety?

I'm inclined to just wire my side markers straight to the park lights, and skip all the trouble of making them "winkable."

Re: How do the side marker lights work?
 

all factory . flash when turn signal is on and if headlight/markers are on flashes also with turn signal .

Re: How do the side marker lights work?
 

It was a period correct safety feature to have the side marker lights flash.
The side Markers on my 1970's VW Rabbits flashed.
My Dart Demon side markers flashed as well. IIRC my 78 Power Wagon marker lamps flashed.

Same function as the turnsignal chevrons on the GMT800 side mirrors and the amber lamps on the T900 & K2 side mirrors. My Jetta has mirror turnsignal bulbs as well.

I'd just run 168 tungsten peanut bulbs in the markers and be done with it. They last many many many many years. The peanuts in my 1969 Polara are more than 20 years old and they work just fine.

Re: How do the side marker lights work?
 

and with todays crazy drivers i say the more flashing the better . if you remove that function and get in a accident they might be able to get you on this with a good lawyer if someone know it was to be there.