Why not use a shielded 1/4" flat blade female terminal and insert into the plug under the radio? You have three male terminals in the plug supplied with dash harness, power, inst. light and ground. You could also tap into that wire behind the plug and add any type of connector you want.
92146377 would be the ash tray that goes into the smokers kit.
Here is a picture of the plug (service manual shows pt # 7122-6030), only letters on it are A2 and M03FMW