So after double-checking the amber 1157s I ordered for the front running/signal lights are correct, I though I'd pop one into the tail light housing to confirm I didn't receive a defective part. I did not - the ambers work as they should. Check.
Next, I double checked that my no-load flasher will really work under no load by removing the front, side and rear signal bulbs. After doing that, I can hear the flasher happily clicking away, at precisely the same interval, even with no lights to flash.
So I set out to document what states the signal lamps are or not flashing...and I gotta admit I'm a little flummoxed by the result. In short, the lights flash correctly with all LED replacements unless the running lights are on. With the lights on, then the lights do not flash with LEDs in all three locations (front, front/side, rear).
Trying different variations gave me an interesting variety in behaviors...so I made a chart, hoping to see something that would bring a solution to mind. It did not
If I keep an 1157 incandescent in either the front or rear, signals will flash. Or if I remove the side marker light entirely. Ok, the side marker can't flash if it is missing...but the incandescent was so dim, that is not much of a downgrade from it working as it did before. None of those are very palatable. I've looked a bit at the wiring diagram, but I must admit I'm still pretty confused.
It appears that I can't have everything upgraded as easily as just changing bulbs...which is a shame because all the LEDs really do look much nicer.
I am so close. And yet...not that close at all. <sigh>
77 Wagoneer and 97 TJ.