Need a wiring diagram for a pronto 51 speed control switch

8 flashes is a Controller Fault

https://www.manualslib.com/manual/723349/Invacare-Pronto-M50.html?page=25#manual

https://www.google.com/search?q=m51+pronto+sure+step+flash+codes

The diagnostic code would indicate a bad control box. It could also be too low a voltage from the batteries or a bad or broken wire or connector between the joystick and the control box. Chair will need a technician from a good dealer to help out if battery's and wiring are good.

You will need to contact a service tech in your area to do this. They should have a special programmer box that can adjust the settings on the chair to improve the chairs performance.

Error Code 9 is a "Communications Error". The controller, or "Little black box" down inside the chair is not talking to the joystick, etc. First, check all the connections. Unplug, examine and clean all of the connections going into the controller, and the joystick connection too. Inspect all of the cables for damage to the wiring. If all looks good, then you likely have a bad controller....ouch. These are very expensive to replace new. You might be able to find a used one on Ebay, etc., or you could be better off looking on sites like Craigslist for a complete powerchair replacement. I have found near-new chairs for under a thousand dollars. Search for Pride Jazzy chairs too...a lot more of those for sale than Invacare chairs. Good luck.

Power chairs are not designed to operate while they are plugged into the charger, as it will drag the charger around or you may run over the cord, therefore most power chairs have an inhibit feature that prevents the power chair from moving while it is connected to the charger.
If you saw sparks from the joystick, something has shorted out the controller; moisture or condensation may have gotten into the controller or there may have been a manufacturing defect.
I do not think there is anything you can do at this point except to contact the manufacturer or the place where you purchased the power chair to arrange a service call and replacement of the joystick/controller. If your insurance bought the power chair for you they may cover the repair if it is not covered by the warranty.
Good luck!

Check that the speed control on your joystick is set to high. If it is then you probably have a battery problem. Even with all the lights lit on the joystick you can have one battery of the two on the chair that is not charging fully. This will cause the M51 to creep and not work correctly

Why don't you download for free it here: http://www.phc-online.com/Pronto_Wheelchair_p/m51p_powerchair.htm

the batteries were dead

The chair has two levers, one for each motor, that disengage it for freewheeling, or pushing the chair without power. These take it out of gear. Place the levers in the locked, gear-engaged position and it should go for you. Here's a link for the manual for your chair, and it will show you where the location is to place it in gear.http://www.invacare.com/doc_files/1125085J.pdf

How many times does the service light blink.