if the horn works, the relay, if there is one, also works....relays on horns must be a later thing i haven't seen a horn with a relay, but my exprience is all 1971 car.
did you check for continuity with the switch off the wheel or bolted down. Happy to admit i don't know these switches but does the switch complete the circuit by shorting the wired contact to the metal of the wheel when pressed? i.e part of the switch sticks out of the bottom side and hits the wheel when pressed.
if that is the case does the wheel boss have the contact and track on the back that runs on the tiny brass wheel that stands up from the idicator/flasher switch... if it doesn't then your issue may be that the wheel/column is not connected to the circuit that comes up to that brass roller therfore any switch trying to complete a circuit by shorting to the wheel will not work.
i only have experiance of the tuff wheel set up used in Australia (it uses the USA Tuff wheel switch and similar style wheel on RT cars, that in non RT form also used the kind of wheel you have. This is a 1971 car and nothing changed much until 1976 i'd expect Mopar similarities to exist between continents)
A wire runs from the base of the wheel boss up the inside of the can, to the switch in the middle of the wheel and the circuit only works if that brass roller on the flasher switch ,runs with its spring compressed to provide good contact pressure, on a nice clean contact groove pressed around the splined area on the back of the steering wheel boss.
Which in my case is an identical collapsible can like a challenger has. in fact i'm running a USA one with the cancel cam moved round slightly to fit my RHD set-up, the cancel cam (thick steel spring wire) is used to pin the contact track in place.
mine worked when all cleaned up so i never worked out if the sprung roller to wheel boss part is a 12V supply or an earth. but it doesnt' really matter so long as all parts are there.
lack of contact at the brass roller can be
1) its missing or broken
2) the wire in the can is not connected properly to to the contact on the base of the can
3) the circlip at the top of the column shaft under the idicator/flasher switch housing is out of its groove and you have up and down play in the steering shaft that allows the steering boss to be higher and further away from the roller than it should be resulting in no contact, the slip joint pot coupler or rag joint between shaft and steering box spline can allow this with no detriment to steering .
on a 70s car the column is mounted on plastic break free mounting and is gasketed at the bulkhead, the cntre shaft doesn't connect elecrically at the pot coupler, don't assume continuity between steering column, (any part of it) and chassis ground.
on a car like mine that uses a chevy style rag joint rather than the USA car pot coupler. there is a wired connection between column shaft and steering box spline sections of the rag joint. this is likley to be a hang over in 50s/60s technology as they never adopted the pot coupler used in the US in Australia.
the metal drive studs mounted in either side of the coupler have a copper contact under them and a wire bridges the rubber disk that sperates the column side from the steering box side.
adding an earth strap from column case to chassis may work... but that is a guess and may be none standard
column needs to be earthed
for it to work
so in my view and in summary
switch needs to connect to wheel when pressed
switch needs to be connected to wire that runs up middle of can
wire in can needs to connect to contact on base of can
contact on base of can needs to be clean and connect with brass roller on idicator switch....
to make sure the lot connects to whatever circuit is below that
you know that this circuit works by removing the whole switch and steering wheel from the equation by shorting the wire to the horn and geeting a beep..
Dave
