Stop in for a cup of coffee
The horn relay should be under the dash, mounted on the driver's side wall above the bottom of the dash, just before the air duct, but may be blocked by the fuse block... You may have to remove the driver's kick panel to access or not... The kick panel is off the kid's 71 valiant that I just verified it on... My 68 cuda is too buried in the back garage to look at...
For the back-up light switch, it comes out the Bulkhead cavities C & D... I show them here from page 8-108 in the 68 Plymouth service manual. These are the top two connectors on the bulkhead that I have circled in red. I traced the back-up light switch wires in purple for you also.
The horn relay should be under the dash, mounted on the driver's side wall above the bottom of the dash, just before the air duct, but may be blocked by the fuse block... You may have to remove the driver's kick panel to access or not... The kick panel is off the kid's 71 valiant that I just verified it on... My 68 cuda is too buried in the back garage to look at...
For the back-up light switch, it comes out the Bulkhead cavities C & D... I show them here from page 8-108 in the 68 Plymouth service manual. These are the top two connectors on the bulkhead that I have circled in red. I traced the back-up light switch wires in purple for you also.