Could be for a siren. Some modern police cars have hidden starter safety buttons in the floor so it could be something like that too.

It wasnt uncommon for smaller police departments to buy their own non-traditional police cars, some even used their own personal vehicles

Cool find

68 Valiant 408
69 Charger 318
69 Cougar 351W
70 Torino GT 351C
71 Country Squire 351W
71 Road Runner 440+6
71 Satellite sedan 318
73 Duster 318
73 Challenger 383
77 Grand Prix 455
83 Malibu 9C1 383
84 Delta 88 403
87 Grand National
96 Ram 360
09 Crown Vic
10 Challenger R/T M6
15 Challenger Hellcat M6