LED bulbs
when used alone in a circuit (installed in a vehicle that wasn't designed to use them)
usually don't draw enough current to allow the original turn signal flasher to do its job properly but if you still have
a mix of LED'S
AND INCANDESCENT BULBS in the circuit (LED/rears, incandescent/fronts and in the instrument panel for example) they
may still work, but would tend to flash more slowly.
(If you have
many more LED's replacing the original single incandescent bulbs that have a TOTAL similar electrical draw to that of the original incandescents in the circuit, the flashers would tend to work properly-but it takes a LOT of LEDs to do that.)
There are different flashers that can be used to replace the original one (that was for incandescent bulbs) when replacing incandescent turn signal bulbs with LED's.
The same thing (a difference in speed of flashing) can sometimes happen in vehicles designed for and using
only incandescent bulbs, with a trailer towing wiring setup-if the flasher IS NOT CHANGED when the trailer is hooked up. With the trailer's
extra electrical load on the flasher (if it is also using incandescents) the turn signals may flash more quickly.
If the trailer wiring was done using a
higher capacity flasher, (to compensate for the
additional trailer bulbs load) the turn signals would likely flash more slowly when the trailer is NOT hooked up.
(If the trailer does
NOT have incandescents but the vehicle still does, the TS would probably still function properly)
Here's a good article on how flashers function, which explains why they can change their flashing rate.
This article explains how turn signal flashers work with LED lights and how to choose the right one for LED applications.
www.thomasnet.com