Not trying to state the obvious, but check to make sure the bulbs are not blown, or wrong amperage. The signal wont click in the dash, or trigger relay to flash if the bulb's in the tail lights amperage draw is too low. Also I believe too high resistance in wiring harness to the signals can cause this as well.

Had this intermittent issue with my 89, but when plugged into a trailer the turn signals were strong and fast. Try slightly higher wattage bulb maybe.

99 Gen 2.5, fixing blown head gasket
89 SWB- 33's, ARB Front locker, SR rear locker/axle, SR F brakes, winch, WST Offroad Armor all Around, 2.85 Aussie T-case Gears (SOLD)
Sold: (2) 95 SR's, 86 SWB, 90LWB, 91 LWB
-Can Change a timing belt in my sleep..