Having a problem finding what is wrong with my 35 GDSD. Will not start and I just changed the ignition switch. How can I test starter or silenoid?

Does it turn over or just nothing when you turn the key? If nothing, you can take a screwdriver (be careful, it will spark) and jump the post from the soleniod to the starter. The two are connected by an exposed wire that could be corroded. This will tell you if your starter is getting power or not. If it turns over, your problem is before the starter. Either the soleniod, battery cables or ignition circuit somewhere. If it doesn't, it's probably your starter.

as wilson stated, look on ur starter, there is a small terminal which is positive, and a stud with a nut which is ur negative. take a screwdriver and make it touch both of em. if it spins, ur problem is elsewhere. i dont think it will start like that tho..mine wont.

With the key on, I think it should start.

it may, but even with the key on mine never would

Thanks guys for all the input. It ended up being that my negative terminal on the battery was dirty. I cleaned the positive and neglected the negative. It cranked up after a good scrub of the terminal. Needless to say, I felt like an idiot!

Figured I would post up a similar experience.
Took my rig out yesterday and after running a few hours couldn't get it to start. Checked out my ignition switch, kill switch and tried to jump the battery but nothing at all. The winch trim would go up and down but the clutch and the "click" would not sound when I turned the ignition key. Took off all my "battery" connections and even tried shorting out the starter terminals with a screwdriver but got no juice to it at all.
Ended up being dead in the water and had to use my trolling motor...
Anyway, got home and took a jumper wire directly from the positive terminal of the battery to the starter and still nothing. Then hooked the jumper wire to the negative terminal of the battery and viola, got a "click". Turned out the ground connected to the frame was bad...
Had it fixed in 5 minutes but what a season I've been having with my rig.