Do you have one of papajamma's circuit schematics for your Spider?
On it, for my 1976 Spider the 3-pin flasher is marked as "C" going to the turn signal switch & e-flasher switch (which sources a "flashing" 12 VDC for the lamps), "R" goes to the indicator on the dash, and "+" to a fused 12VDC.
The cheap CF13 JL-2 flasher for LED loads I used connects with it's "B" terminal where "+" is, "L" on the flasher goes to the "C" connection wire, and (this is the tricky part!!) the flasher's "E" connection goes to the "R" wire... but the flasher draws so little current on "E" that you must use an LED, oriented correctly (+) side to the flasher, (-) to the dash indicator, in place of an incandescent lamp.
I used a 10mA green LED in my indicator lamp holder, and it lights nicely.
50 years from now - how are we going to restore a "classic" microprocessor based modern car?? Alfas - 1980 Spider, 1987 Milano, 1976 Spider