Can you be more specific about 'electric musical instruments'? Do mean like electric guitars and basses? Something like the Theramin, perhaps? Music is my hobby, more specifically live sound and production, and I play a little bass guitar.
Based on that, I think you might be better served in reaching your goals by getting work at a manufacturer of electric instruments. You won't have to deal with the dangers of trying to work in a construction site, and it will be easier for your employer to accomodate your abilities. You need to be realistic in this...you really don't want to be the guy that the company is looking for an excuse to lay off because it cost them more to accomodate you than you are able to produce for them. Business is business, and constuction contractors are tough people in this regard.
But more to the point of being on the offense rather than defense, I think that working from the ground up at an instrument manufacturer will be worlds more enlightening for you. There are different cultures in the music industry, and that's a big part of what you need to fully grasp as an instrument designer. And learning how a manufacturer will build what you design is huge...you want to design instruments that are economically possible to profit from.
If you want, PM me and I can give you info on a web forum I moderate. I know a member who's an EE who designs instrument amplifiers for a company that's a division of Fender, and also has extensive industrial power systems experience. There are other members who are music industry players in various fields, who might be of interest to you.