Mower will not crank. I have a gravely ZT 48 HD In the on position when you sit on the seat it double clicks. When you turn it to the crank position, it does nothing. Any advice?

The best thing to do it to go and visit your local stockist.

https://saffordequipment.com/product/gravely-zt-xl-52-zero-turn-mower/

https://www.google.com/search?q=Gravely+ZT+XL+mower

..

does the engine crank or nothing at all?

Zero turn mowers in general require the following.

1. PTO off.
2. Steering levers to neutral position.
3. Parking brake engaged.

A good habit to learn is; When a zero turn won't crank, cycle all the start engine interlocks. Move park lever off/on, steering levers out/in, PTO on/off.

And a simple basic electrical check is; With key in run position (engine not running), you should hear the electric clutch engage/disengage when PTO switch moved ON/OFF.

I'm not saying the gas filter is your problem but you might want to change it. Could be hindering you.

Sounds like a low battery, enough juice for the hour meter but not for the starter

If you want to solve your problem, click on the link I attach-

Best Manuals

You just go to the link I attached I'm sure you will get the solution of your problem.

Greetings, I read your question and I think Reliable-Store can help you in this. Here's the site link -

Best Manuals

Seat switch is under the seat.

It sounds like the seat safety switch is the problem. Tilt up the seat and make sure the plug to the seat switch isn't loose or off completely, and that the switch is firmly mounted. If everything seems ok, remove the switch and test it with a multimeter. The circuit between the switch terminals should close when you press in the button. If not, replace it. Good luck!