If you don't have a hole in your dash frame in the obvious location for a reverse light, then the bulb may go to something else. Can you take a picture of the component you're referring to? It could shed some light on the subject...

Troy
Houston Mopar Connection Club
'69 Charger Daytona 440 - auto - 4.10 Dana (now with 426 hemi)
'69 Charger 500 440 - 4speed - 3.54 Dana
'70 Road Runner 383 - 4speed - a/c (now with 440)