Problem:
When I hook up something to tow behind my Jeep, the turn signal lights flicker rather than flash. Just the turn signal lights....

Not a problem:
running lights are fine, bright as can be, same for brake lights - they are about the same as the 4-ways, they work fine as well

Thoughts:
I have a Super HD flasher and a 15 amp fuse.
Towing wiring harness ground on Jeep is connected to the neg term of battery.
Other wires are solder spliced to the origional wiring harness for the tail lights.
All trailers towed have grounded light fixtures, hardwired into the ground lead on the harness.
All trailers towed don't have this problem when towed behind (SHUDDER) the ford ranger, explorer or the buick.

I have tried:
Verifying ground is good
used several different light set-ups (mounted, unmounted, magnetic mount)
upgraded flasher from stock to HD and even tried a Super HD one....
Tried different trailers

Surely someone has a simple answer for this one....