The ends of the flat cables that plug into the print head must be clean as well as the connector on the head they plug into. On the head connector itself that is not easy to clean. You would probably need to remove the head to get at it good. Of course be very careful not to touch the nozzle plate. Personally, I'd remove the head, remove the manifold from the head, then use an old toothbrush to thoroughly clean the top of the head and the connector with isopropyl alcohol. Again, be careful not to hit or touch the bottom nozzle plate and avoid getting any alcohol into the ink chambers of the head while the manifold is off. Make sure the alcohol is all dried/evaporated and put it back together. You want to keep the head out as little as possible as well to avoid the ink in it drying out as much as possible. Might even wet a
paper towel with solvent cleaning solution and set the head on that to help keep the nozzle plate moist.
Also - just to be sure, you did reconnect the small head memory ID board too right? If that board also got ink all over it I'd probably clean it too.
Worst case - the wet ink on the head shorted the head when you powered the machine up and fried the head. Much worse worst case, that wet ink shorting things also possibly damaged the slider and/or main boards.
I'd have to say though - you said you got cleaning fluid on things. The photos look like an ink explosion all over everything. That is a complete mess and I'm not at all surprised you are getting an error. I cannot show you how to do any of this though. If you understand these things then you are capable of doing these things, if you are unsure then you probably need to get a tech in there who can.
Also - in the second photo the head cables are not even connected to the head. One other consideration as well - if the head cables have been sharply bent where the blue reinforcing piece is on them there is a good chance the cables are internally cracked and damaged which will also cause this error. The flat head cables are delicate and if at all possible should never be creased. Mimaki even had a tech notice on them at one point to add a padded reinforcement in a couple of spots and a warning about creasing them.