[mr0077]

Whaler, basically, you want the relay to send power to the fan so that the fan can run when the t-stat tells it to OR whenever you want to switch it on manually, right? If so, you need to control the relay to do that. To get the relay to run when the t-stat tells it to, you should run battery power to the relay instead of your yellow switched wire, and have the small black (grd) going to the t-stat. Then, to turn it on manually, have one side of the toggle switch hooked to the small black and the other side to ground (bypassing the t-stat), like Kris K describes. If, for some reason (?) you want instead to interrupt the automatic t-stat control (so it you can turn the fan OFF manually with the switch - NOT RECOMMENDED!), the toggle switch should be in-line on the line to the t-stat, and would open or interrupt the ground between the relay and the t-stat.
Wiring's a pain...LOL