I'd go with a basic circuits electrical course, like previously mentioned once you understand the basics you can work out the rest either 12vDC or 120vAC, their's ohms law and about 10 other laws/rules and the ability to use a calculator and VOM.
welding is 5% knowledge and 95% practice, a realy good basic course will teach ou how to light and adjust an oxy acetelyne torch. make a puddle,travel the puddle and then add filler metal with your other hand, once you can do that you will learn how to strike an arc with a stick welder,start your puddle and travel the puddle while maintaining the arc and adding filler from the sacrificial electrode, tig welding is like ocy acetelyne except you use an electric torch instead of a gas torch, strike an arc start a puddle,travel the puddle while adding filler metal with the other hand. mig welding you turn the machine on grab the handle touch the wire to where you want to start and pull the trigger, &travel the puddle.
that's the basics, you have to play with the machine adjustments and practice, the advantage to taking a course is that you don't have to invest in equipment until tou decide if welding is something that your comfortable doing
FYI just so you can't say no one told me, if you melt steel at 2300f sooner or later your going to touch something hot and get burned
a good basic mechanical maintainece course will be more beneficial than an diesel course.