Yes, the relay (very heavy duty and repairable) in an 84 Ram D150 is on the fuse block in the cab.
I assumed the horn would blow whether running or not, but still haven't found a lead that gives 12 volts when the horn is pressed on the steering wheel.
It is a moot (mute) issue anyhow due to my one and only horn is defunct.
Not even a chirp when 12 volts is applied.
Bottom line: I need a new horn or horns before I can cipher the proper wiring.
The Chinese horns out there don't thrill me none, either.

Found a new old stock *Freeway Blaster* *Big Rig Sound* Made in USA horn on eBay and it sounds great!

My horn ring worked and my relay (on the fuse block) worked but still could not find the wire (DG/RD) on the engine side of the firewall.
I ended up splicing (in the cab) into the side of the relay that gave 12 volts when the horn was pressed, ran a lead out to the horn, and voila!