my '73 Travelall has a new starter, but that didn't remedy the problem not starting when turning the key. There is a pronounced single click sound in the dash to the right if the ignition key when the key is turned to start the car. After several tries it eventually finds a sweet spot and starts. Whats making the clicking noise in the dash?
An automatic '73 t'all would have a t-407 (tf 727) automatic transmission. Those use a "neutral safety system" (nss) of course so that the starter will initiate only when the selector lever is in park or neutral if the shift linkage is adjusted correctly. The borg warner automatic used in '72 and back fullsize stuff uses a totally different form of neutral safety start system.
The actual nss switch is mounted on the driver side of the transmission and operated by the shift lever from a cam inside the transmission. But the position you describe where you are hearing the clicking sound is the relay that is a component of that circuitry. That relay is identical to the horn relay and the parts are interchangeable. It clicks every time it operates, but since the starter is normally initialized you don't actually hear the relay click over the noise created by the starter and then the engine cranking over.
That relay is a common part available at any auto parts outlet, ask for a "horn relay", a typical standard motor products p/n is hr117.
Since all pickalls leak water through the cowl from the factory, water builds up on some body seams behind the dash and runs down into the electrical apparatus and the dash fascia. I've seen many cases where water drips right on that relay and of course rots it over time along with the connectors. So simply locating and cleaning the contacts on the connectors sometimes fixes this issue, otherwise, replace the relay with new.
Also, remove and clean the connector on the nss switch itself.
Bulkhead connectors on any IH product can be problematic...but a pickall setup is somewhat different compared to a Scout II which is total steaming pile! It is possible for the relay to energize (the click sound) yet switched current not be applied to the starter solenoid terminal if the bulkhead connector contacts are crapped.
