I am building my own speaker for he first time.i have 2 subb woofers/mid and tweeter but only ave three way cross over what would be the best and safest way of wiring up the speakers?

Hi first thing: do you have a passive or active crossover??

1. Passive crossover: you can connect the two output together to your subwoofer to have in the same time the low bass and the mid range of frequency.
2. Active crossover: NO solution you have choose one out put of your crossover, i guess the best is the low output, but the choice is in your hand try the the two output(low/mid) once and choose the best for you