Thats were the flasher relay goes, a three prong relay should work, but i'm not certain, the flasher on my bike was replaced with a BUSS FLASHER 12v No. 550
Edit: found some more info on the flasher I have from another site
Manufacturer Number:
Bussmann NO.550
Cross Reference:
IMP 080102, IMP 080104, IMP 80102, IMP 80104, PAI FSF4267 U80 091204
Description:
Variable Load Flasher •Thermal flashers, which use heat build-up to flash circuit on and off.
•Operates correctly under variable load - flashing the designated vehicle lamps only; or additional lamps when a trailer is in tow.