I'm running 2 car horns on my 2013 RT, using the un-modified OE horn circuit & switch to trigger a fused relay supplied & earthed with power direct from the battery thru heavy leads, cos without the full-on 12v power supply (& earth), they sounded pretty anemic!
Sorry, can't help with where the OE Horn & circuit is on any F3, my Forgetory is working too well for that tonight! :banghead:
But
YES, exactly as BajaRon & Gwolf say above; if you can find some place to fit them, they can be made to work, only I too would
strongly recommend that relay & heavier wiring to provide full-on Green Steam 12v Power triggered by the OE Horn circuit!!

hyea:
Good Luck! :cheers: