I have a Lionelville Pipe Con where the forklift “loads” the pipe. I have it hooked up to my MTH z-1000 accessory power. It works but the forklift is very fast. I assume that is because it doesn’t need the 12-14 volts is more than it needs. What would be the best/easiest way to reduce the power so it slows down?
I don't have your specific accessory but there have been many OGR threads that discuss the general application of the lowering the AC voltage to operate an AC accessory. I'd say the top three methods are:
1) Dedicate a surplus variable AC transformer that you get from a swap meet for $5-10 and dial in the voltage that works.
2) Splice in a Lionel rheostat into the "hot" wire going from the Z-1000 brick fixed 14V to your accessory. This allows you to adjust the power into the accessory. There are/were several versions of the Lionel rheostat and again $5-10 at a swap meet.
There are modern versions of the rheostat though not specifically designed for O gauge use. For example, see this OGR thread.
3) Splice in multiple diodes and/or bridge rectifiers in the "hot" wire. Here's a photo from this OGR thread where the topic was essentially exactly what you're asking about.
Then there are special cases which may or may not apply.
a) If you have a meter and are handy making measurements, you can sometimes calculate ahead of time how much power/voltage reduction you need Then you can use a "fixed" version of method 2) and 3). This could save a few bucks.
b) If you know that the accessory can operate on DC voltage there are inexpensive AC-to-DC adjustable output voltage converter module (again about $5). Notable exceptions that require AC voltage are those with a vibramotor (or whatever they are called) where the mechanism vibrates a platform or whatever to induce motion in the accessory.