i installed my own manual fan switch and i spliced into the blue wire, which is the high speed fan. when i turned it on, i noticed that only one of my fans is working. is this because one fan is the high speed fan and the other is the low speed fan? or should they both turn on regardless of which speed its on?

 

one fan is high and the other is low you gotta splice into 2 wires

 

went out and spliced into both wires and theyre both working now. thanks.

 

No, it is not that way at all.

You have to splice into both fan relay control wires, because of the way the relay system works. Grounding the high speed wire is going to result in high speed for the RH fan only (just like the OP found out).