Some of the LED specific 3 prong flashers have a separate ground wire for the electronics inside the can. Any chance yours is that way?
If you are reading 9 volts on the wire between the flasher and power with a regular (not electronic) flasher you'll never get enough current thru the bi-metallic strip to heat it up and make the flasher work. As a troubleshooting step, disconnect the flasher power wire from the headlight switch and hook it directly to the ammeter + side to see if the flashers work there
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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