Mazda B2300 '96 2 wheel drive 5 speed (Relay or Switch?)

Here's the deal. Every so often I would get in my truck to start it up and notice that my clock and radio have defaulted as if the battery had died. But my truck would run fine no battery lost from what the gage is telling me. So I checked the battery and notice alot of corrosion on the heads and connetors. I started to clean them. I go to start my truck up, and I get alot of repeating and loud CLICKING sounds as long as I have the key turned. So I install new connectors to the heads, and still get the samething. Next I pull the starter with a solenoid attched and take it in to be tested and it passed. Dealer suggest that the Relay needs to be replace. I can not find a relay anywhere, not even the web. But I did run across a website that was calling it a switch. So is it that I'm looking for a switch or a relay? I just found out also that there is a switch or relay for the solenoid which is attached to the starter. Should I purchase one for the solenoid too? Please Help