The horn switches on that steering wheel is two strips of metal the length of the three arms (3½ inch long? each) with a piece of foam between the metal strips. The foam collapses to allow the metal contacts to make the circuit. In this case, that foam deteriorates over time and allows the two strips to make contact on their own (which is not good). It is not a hard fix but cumbersome sense all three strips are held together with wires that are joined in the middle.
"If memory is correct, looks like this"
View attachment 35607
The part number for the switch is P147MX9. It has been discontinued by Chrysler for a while, but it appears a few might still be out there. Retail price (if found) is $54.50 (US).
View attachment 35608
(three switches and three covers)
The part number for the spoke cover (vinyl?) is 4019457, which was only recently discontinued by Chrysler. If a dealer has one, the retail price is $13.50 (US).
Mopar NOS 1976-79 Plymouth Dodge Chrysler 3 Spoke Wheel Horn Switch ALL P147MX9 | eBay
Set of (3) Mopar Dodge Horn Buttons Button Pads Part No. 4019457 OEM 26577 | eBay This one is marked as a spoke cover, but it is for a switch and three spoke covers (mismarked). This one is not bad price wise, so I might recommend getting it, rebuilding it and your existing switch, and placing the spare switch in a vacuum food bag (to prevent air damaging the foam). The spare should last forever without air touching it.
Also, be sure to clean the metal contacts before assembly.
BudW