I'm not sure if 68 Dodge is the same as 68 Plymouth... On my 68 Road Runner (column automatic) the reverse light switch is located at the very bottom of the steering column by the firewall. There is a small plastic spike that actuates the switch. It is easily lost or broken. You loosen the attaching hardware to rotate for switch adjustment.
Yep that black post broke on my '68 Road Runner column automatic. I found the broken post and repaired it with a sheet metal screw through the center of the broken post. Then found a new one and held on to it if the repair didn't hold probably still in the glovebox still waiting for the call.
