ok i have 2 am remotes and and only 1 crystal for the remote and one for the car. now i wanted to switch the remote crytal to the other remote so i took it out then put it in the other remote and nother happened it didn conect? any idea

Are the transmitters on the same base frequency band? Like 27MHz, or 75MHz, etc? What model transmitters do you have?

its a xp2 2 chanell radio am and i dontno the mega heartze it ses on top on the crystal 27.145 / a HI tec am 2 chanel remote name is Aggressor this one is 75 megahertze

Sorry, I don't think the crystals are interchangable between 27MHz and 75MHz systems.

Need to pick up an appropriate set of crystals for the other radio.

And it will require a matching receiver in the RC, same deal as the transmitters, needs to be on the same base frequency band.