I thought it's a power supply issue since the heatbed requires a high power draw. We still don't know exactly what part was culprit. If you installed the 5th tool head and the issue is back, you might want to swap power supplies.

Seems to be the heat bed imo. I noticed it started working when you fiddled around with the wires and the toolheads. Can't be the boards either.

Is there like a waterfall nearby?

I thought Prusa had good support? Why didn't they help you with the troubleshooting?

Glad to see you have a working printer! For troubleshooting, the vast majority of the time the issue will be an active component, such as a board, vs. a passive component, in this case the wiring. I am not sure about the heads, but my money is on the board for the heatbed, like @huntliba. The heatbed board also draws the most power of the changed components, so in theory it should have the most impact on the operation of the printer. Best wishes, and I really would like to see some prints after all this work you've put into it.

On my XL I had a damaged CAN Bus wire for the controllboard of the heated Bed. That caused a short in the CAN Bus and Killed almost all other Controlboards

Did, at any point, Prusa offer you a full refund or a new printer?

any heat bed heating needs to be done with the build plate installed.

You still don't know which of those 3 changes is truly in fault... I would but my money on heatbed board but yeah... atleast you got it working...

So.. you have 2 now? damn.. don't like so double down? keks. Good on you, what I don't like seeing is a company who puts out a printer (Prusa/Creality/ etc) and they make YOU do their work for them. Bare minimum, they need to plug boards in a test them prior to sending out to you. They tout how Prusa as a company is so thorough.. this used to get them points when compared to a Creality who just plain sucks at everything, but now.. they have def fallen into Creality territory with their quality.

Prusa is not good value for money. I guess its cool to be able to tell others that you have a prusa, but they have definitely gone down hill as of late. Between moving away from their open source roots to the quality control issues they now seem to have, the tax they demand just isn't worth it anymore.

for as much as this printer cost y doesnt it have a touch screen, lol, for the cost it shouldnt be missing any feature that can be put into a printer

Jesus this audio is garbage