So i decided to hardwire my Pro 78 to my 2003 Pontiac Grand Am:
I used the kit that came with the radar detector and also bought a fuse tap from Autozone. You basically remove your existing fuse (10 Amp for me as I used the Interior Lamps Fuse) and put this adapter in. Then there are two slots for two fuses. One of the slot is for the original fuse that was in there b4 (the 10 amp) and the other is for the other accessory that it will be going to.
I used a spare 2 Amp fuse that came with the car for that slot, even tho the Pro 78 Hardwire Kit is already fused, the adapter still needed another fuse to operate.
In the Picture, it looks like the original fuse don't fit the new slots. Your right. I think you have to buy small fuses so they fit in all the way. I was still able to use the original fuses even though they don't go in all the way. They are in the slots pretty securely and are not likely to fall out.
I ran the wire from the Fuse box through the weather stripping on the passenger side, and to the Radar Detector. All in All, I think I did a pretty safe install, despite the fuses not fitting properly. The worst that could happen is they touch and I have to go spend a few buck to replace them.
The Fuse tap cost me $7.
Here are some Picture I took during Install (High-Res Warning for Dial-Up Users!):
Fuse to Tap off of (10 Amp Interior Lights Fuse): [replacer_a]
Fuses Installed with Adapter In Place:
Ground Bolt (Also better Pic of Fuses):
FINAL Install Pictures: