OK, here is a primer...the multiple contacts on the hotshoe of the camera permit flash dedication features between camera and flash...things like
- camera senses flash is on, it changes suitable shutter speed for flash
- camera sees flash is ready to fire, it lights the ready light in the viewfinder
- camera tells flash what FL and f/stop are set on the lens, so zoom head is set for proper coverage and max distance at that f/stop is displayed on the flash LCD panel
- ETTL commands such as preflash and power level to fire at time of shutter release
- trigger the flash to fire
So an extension cable with all the contacts permits ETTL control of the flash, if want to use it...but you do not HAVE TO use it! The small contacts in the hotshoe deal with the first four functions in the above list. The large contact in the hotshoe, and the metal part of the hotshoe which holds the hotfoot, are the contacts for function 5 of the above list.
A radio remote which uses only the PC cable (not the hot shoe) only does function 5 in the above list, so the flash itself has to be set on Manual flash, or set to Auto photosensor mode (Canon calls this 'External' mode!). Alternative to the PC cable for triggering is a hot foot which has one one contact in the center which goes to the large contact of the hotshoe, plus the metal contact which touches the side metal of the hotfoot.
Since you have a Tn which has no PC connection, you could buy a hotshoe-to-PC adapter which goes in the hotshoe of your camera, and the PC cable from a radio trigger plugs into that.