Park and turn signal light issue

I was convinced I thoroughly checked all my lights before I covered all the wires in plastic sleeves, yet somehow I've now noticed the front park lights are only park lights when the lights are on. They function fine as turn signals with the lights off. With two filaments they should be capable of both at the same time(both are burning with the lights on regardless of turn signal activation).

The side marker lights are wired into the same feed. They function as marker lights and turn signals(they work with the lights on, but only one filament, so only a turn signal then). They are only two wire sockets, not three like the originals, but Painless claimed that due to the difference in resistance of the bulbs, the lack of a ground would not interfere with the front marker and that the side marker would use the same ground as the front. Are they mistaken? Do I need an independent ground for the side marker?

The front marker sockets have 3 wires, I could have wired them incorrectly, but surely then the filaments would still act independently? I'm sure there is a correct way, one filament appears brighter than the other.

I'm lost.  You are running a Painless harness?  Can you tell us how you wired it with respect to the wiring below?

I think you are lacking a ground.  What usually happens is that w/o a ground the light works when the headlights are off as it grounds through the low-resistance headlight's filament.  But when the headlights are on that doesn't work.

I agree with Gary.  sounds like a ground issue.  can you do a schematic of your wire setup?

If your side markers function as turn signals, the turn light is getting it's ground through the side marker bulb. GM has done this since the 60's, to improve visibility from the side. Painless wires lights in GM fashion so that you have this feature. It sounds like your park light doesn't have a proper ground, because it looses it's ground when the side marker bulb is powered.

I thought the original lights functioned the same way as my original side marker had 3 wires, though looking at the schematic Gary posted that doesn't appear to be the case... Do the stock side markers work as turn signals?

I'm looking for those original side marker sockets, but I think I disposed of them...

So right now the side marker/turn signal has no ground, only the front park light/turn signal has a ground. Both work fine as turn signals with the lights off. With the lights(headlight or park) on, only the side marker functions as a turn signal and both filaments on the front park light are continuously illuminated. Will grounding the side marker fix this, or do you think there is a fault with the front park light ground? I suppose it's also possible that the aftermarket park light sockets are faulty...

I can post a schematic if you wish, but it's really simple, the turn and park light feeds are split to the two sockets, with a third ground on the front socket.

Rob,
Perhaps some PO did Dan Stern's side flasher conversion to your truck?

With bayonet based bulbs it should be impossible to lock a two filament bulb in a single filament socket, and vice versa.
Look how the pins of an 1156 are in the same plane and those of a 1157 are offset.

If you had 3 wire sockets before they didn't come from the factory (or maybe they were from an overseas variant)

If the ground potential is high, the more resistive filament is not going to light up.

I haven't found the original side marker socket, but I did find a picture.



It has 3 wires, but it's 2 park(brown) wires in addition to a ground. One coming from the source and one going to the front park light. So it had no turn function. I believe it was stock.

Anyway, I did some more troubleshooting and figured it out... My eyes are bad! The system functions as it should, almost, the wires on the park light socket are reversed. The park light is wired to the larger/brighter filament and the turn signal to the smaller/dimmer one. Through the lens you can't tell that the turn signal is working with the park lights on. And looking at the bare bulb just blinds you... But looking at it between fingers and using various squinting techniques I was able to discern that the two filaments do act independently as they should. And the side marker acts as a primary turn/secondary marker with the single filament bulb.

I suppose you should be able to do the same with the original sockets and wires if you were so inclined.

Cool!  Glad you got it figured out.