How do I check the transmission fluid on a FLSTF 1994

Nothing specific to your vehicle, but the all have a drain plug at the bottom and a fill / level plug at the side. The bottles of oil have a tube and you squeeze it in until it starts to weep out of the level plug.

https://www.way.com/blog/how-to-check-manual-transmission-fluid-mlf/

https://www.google.com/search?q=1994+Plymouth+Colt%2C+add+transmission+fluid+to+a+manual+transmission

..

check trans while running in park and warn, check trans dip stick under hood and if needed fill thought dip stick tube use a funnel for that do not over fill.

Drain transmission fluid, replace filter and then refill with AUTHENTIC BMW tranny fluid.

Fluid by the back wheels could be an indication of a brake fluid leak. Check the reservoir on the master cylinder for brake fluid level. If it's low, you've identified that you have a leaky brake line and should replace it immediately. If the fluid is full, it's possible that you've a transmission fluid leak that traveled along the undercarriage and is dripping by the back wheels.

For the fastest indication of what the fluid is, check all the fluids, power steering, auto transmission (if equipt) clutch if it's a manual transmission etc

YOU COULD HAVE FAULTY TRANSMISSION NEUTRAL SAFETY SWITCH BUT CHECK TRANSMISSION FLUID LEVEL MAKE SURE NOT LOW .IF ITS BEEN A LONG TIME. CHANGE TRANSMISSION FLUID AND FILTER.TRANSMISSION NEED MORE FLUID IN REVERSE BECAUSE NEED HIGHER FLUID PRESSURE TO APPLY REVERSE CLUTCH AND GEARS.

On the right side of the bike, just under the chrome end cover on the transmission, there is a small drian plug. I may be behind the exhaust pipes. I think it uses a Torx type wrench to remove it. Drain the oil here. Remove the large plug in the chrome cover with a 3/8" hex key and refill the transmission with 20-24 ounces of the appropiate lubricant.

Good Luck
Steve

CHECK TRANSMISSION FLUID LEVEL.TORQUE CONVERTER NEED FLUID TO LOCK UP.IF FLUID LEVEL OKAY.CHECK TRANSMISSION FUSE.IF FUSE GOOD.TRANSMISSION TORQUE CONVERTER CLUTCH SOLENOID DEFECTIVE.OR TORQUE CONVERTER CLUTCH SHIFT VALVE IN VALVE BODY STUCK-OR TORQUE CONVERTER HAS INTERNAL DAMAGE.

your engine and trans share the same oil