I am really trying to get my late father-in-laws' 1988 C4 back to it's former glory and I decided to update the lights. The car was neglected with his failing health and I have done a lot so far but now I am working on replacing burnt bulbs and thought LEDs would be great to reduce the heat. So now I have an issue with the turn signals of course.
Here is what I have done...
LED headlights
LED front turn signals
LED tail/brake lights
Both Flashers swapped to electronic flashers, 2 pin, no ground wire
Several interior lights converted to LEDs (but I don't see how that could have any bearing on this)
NOW FOR THE PROBLEM
Headlights OFF
No exterior lights on
Headlight OFF Using turn signals
Everything seems to work fine. Front (yellow) and rear (red) turn signals flash, front side marker lights flash (yellow), turn signal indicators on the dash flash

Headlights ON (running lights do the same thing)
Both dash indicators solid on
Front turn signal solid (yellow)
Front side marker lights off (yellow)
Rear turn signal bright solid (red)
Rear side marker lights solid (red)

Headlights ON USING turn signals
Front turn signals solid (yellow)
Front side marker light off (yellow)
Front corner lights solid (white) (I think that is how they are supposed to be)
Rear turn signals stay mostly bright solid (red) (there is an ever so slight "twitch" which occurs at the flasher rate)
Rear side marker lights solid (red) (I think that is how they are supposed to be)

Whew. I have read about issues with the fog lights and LED headlights and I havn't approached that yet but I don't think that is part of this issue.
I have read about modifying relay under the passenger side knee panel to create a ground but not sure if that only refers to 1990 models and newer.
I have read about cutting a wire on the corner light and grounding it but again not sure that is for the 1988 year model.
I really hate to ask a question on here that sounds like it has been answered but none of those describe my issue specifically.
Please guide me on what to try...

 

For what it's worth to anyone having the same issue, it all has to do with the LED turn signals. I spliced in a small socket for a 168 bulb to the turn signal. Positive lead off the extra socket to the blue wire on the factory harness and the black wire of the extra socket to ground. Everything flashes correctly and the turn signal indicators on the dash work as usual.
The picture shows the wire on the driver side I tapped in to for the positive side on the new socket.