depends on where you are placing the tweeters and where the signal is coming from.
I put the tweeters in the kick panels and the woofer in the door. I run them off an amp, so I ran new wire to the crossover. I then cut the OEM door wiring and spliced in new wire from the crossovers to the OEM door wiring for the woofer. I ran new wire from the crossover to the tweeter. Not the best way for audiophile sound, but I'm not competing and the hassle of routing wire through the grommet wasn't worth the minimal difference in sound quality.
1992 5.0 coupe - TTI single turbo
1986 Merkur XR4Ti - 2.3L turbo