Need more info. As if, I don't know if your 'switch' is a mechanical linkage, electric, air, or electric over air. That alone entails four very different diagnostic procedures.
PTO or Power Take Off drive lines are limit in terms of gear ratios. If your PTO seems to be rotating slow, perhaps it is not geared correctly for you vehicle or application. ----
PTO stands for Power Take Off.
PTO is a Power Take Off. It's often used to operate hydraulic systems (e.g., the hydraulic pump on a dump truck).
PTO is Power Take Off... if the truck has a hydraulic system (such as dump trucks, wreckers, roll-offs, etc.), then it has a PTO which engages the hydraulic pump.
Not unless it's an electronically actuated PTO system which is run through the ECM. Which is a bit unlikely, as a 1999 MY truck predates SAE j1939 multiplexing.
If you have experience operating a Class 8 truck, you should have the driving part down. If not, I would suggest you go to a truck driving school - you're not going to learn how by simply reading about it. As for the PTO controls, it depends on which PTO system you have. Normally, you push in the clutch, engage the main PTO control, let off the clutch, and use the secondary PTO control to raise and lower the dump body. Some systems differ, however.
There's several different manufacturers of PTO systems out there. In simple terms, you engage the clutch, engage the PTO, release the clutch, then use the corresponding lever to raise or lower the dump body.
International manufactures trucks in classes 5 through 8. How you operate the truck depends on what class of truck it is, what transmission it has, etc. Operating the PTO system to raise and lower the dump bed will also depend on what transmission you have, as well as the PTO system. If you can give a specific model, the answer can be narrowed down.
Need to know who manufactured the PTO system in order to answer this question. It's an aftermarket accessory not manufactured by Freightliner. So, we don't know who manufactured the PTO, what model it is, or what type of actuation it has (e.g., mechanical, pneumatic, or electronic).
This is something you really need to consult a professional about, as the installation of a PTO on a commercial truck will typically require cutting and fitting in the cab floorboards, installation of a hydraulic tank and wet line, etc.
You will probably burn out the hydraulic pump in a short time.
The PTO on a firetruck is used to power the pump, which takes water from a water source (tank on the truck, fire hydrant, or drafted water), pressurizes it, and discharges it through various devices (hose, monitors, standpipes, etc.). On an Aerial or Ladder fire truck, the PTO is used to power the hydraulics and motors that raise, extend, and rotate the ladder. A PTO can also be used to power a generator, which can be used to power high-intensity scene lights, power tools, fans, etc.