What do electricians and mechanics "do"?

• A carpenter does carpentry.
• A scientist does science.
• An engineer does engineering.
• A blacksmith does blacksmithing.

(The grammar of these sentences may be poor; the point is to get the idea across.)

So then:

• What does an electrician do?
• What does a (car) mechanic do?

Or are there perhaps really no such words?

Solution 1:

You may consider that an electrician wires

wire : verb to provide (a building, room, etc.) with wires for a particular service or for electricity

and that a mechanic repairs

repair verb 1a : to restore by replacing a part or putting together what is torn or broken : fix b : to restore to a sound or healthy state : renew

from m-w.com

Solution 2:

It's by no means a 'single word', but many automobile mechanics would say that they do "Auto Repair". Though this of course only refers to the reparations of a vehicle, not the construction of one or the upgrading of one that is not broken.

For the act of working on a vehicle, there is "tuning up", or "bodywork" if you want to refer to only the outer 'body' of the car.

Or you could modify the two, since both individuals are engineers.

You could try 'automotive engineering' or 'electrical engineering', but both of these phrases specifically refer to automotive engineers and electrical engineers, rather than mechanics and electricians, so to avoid confusion, this is only advised if the person's role is already well established by context.