Okay I was worried about this happening, People blowing up the output amp for the speaker by trying to tie their headphone port to a FM modulator or some other output to their stereo...
Well , I am here to save you. more importantly save your BEL vector series from a silent death.
The problem is power, Namely the ground. The output (headphone) on the side of the detector is not meant to be grounded. if you are using a FM mod that has a lighter adapter or is otherwise powered by the car, you will pull a ground through the headphone connector and kill the audio amp in the vector dead. Now this is not 100% of the time as there are thousands of different FM mods. some will pull a ground and some wont.
So you have 3 choices. a) use a power source for the FM mod that is isolated from the cars power B) power the mod with a battery or C) build a cable unit using a cheap audio transformer. this will allow you hook your Bel Safely to your stereo or RF mod..
first you will need THIS from radio shack
Audio Output Transformer - RadioShack.com
I will try and post some hand drawn schematics for everyones enjoyment