What harness? Factory Ford, Ron Francis, Painless, ISIS? ????
Are you using one or two dash indicators?
do you have the diodes placed in the right direction (stripes toward the bulb)?
, check to see if your TS/Brake/Parking bulbs are installed correctly, they can
be "clocked" 180° out of phase and short to ground.
I see you have already disconnected the RT switch to verify it is NOT causing the problem. Try setting up a test scenario with only the rears in play . . . No issues, connect the fronts one at a time, test again. If the rears give you a problem, try connecting them one at a time . . . Test again. Trace your wire harness path and look for shorts to ground (wires pinched or cut thru).
Check ALL your grounds with a meter, bad grounds in our cars cause a multitude of issues.
Are you using LED bulbs? They require an "electronic" flasher, not the older "thermal" flasher.
little block, BIG BLOCK . . .
FFR3712K (POPSDRM) in Lost Wages, NV.
MKII, 5.0, GT40-EFI, E-303, T5, 17" 5-Lug Chrome Cobra "R's", 315's, PBR 4 wheel Disks, Full Tubular suspension, Flaming River, 3.73:1 3-Link, Drop Butt mod, Dash forward mod, Footbox Air vents, Custom Turn Signals, Custom 4-into-4 headers, Non-Donor build, Ford Royal Blue Pearl w/ Arctic White stripes.
Last edited by Big Blocker; 08-24-2012 at 01:22 PM..
Reason: added another question.