It's a pikey fix. Take the wires out of your relay socket, check that there are three contacts in there, plug your new one in and away you go. You'll be in flasher heaven...
Think yourself lucky. My 68 has a really wierd wiring setup and a 9 pin indicator relay. It was broken and I had to make the circuit using 5 relays.
Blimey, that looks like fun! I'm going to remove the existing relay and extra wires on Monday and add the new relay into the fuse box, and see what happens.
And my fuse box, if you could call it that, is tucked up under the front of the dash so you can't see it without a mirror. What were they thinking! That sounds the best idea, I expect it was an MOT fix and that one was lying about.
If I post the original to you, could you have a bash at mending it? You're a bit of an electronics whiz aren't you? It looks like a capacitor or a resitor has burnt out, it's a very fixable unit if only one knew what they were doing. Reminds me when my old Selmer valve 100W pa amp went wrong. My dad is a chartered electronics engineer, but knows nothing of amplification. As he prodded with meter he shorted out a mahoosive capacitor which went off with a loud bang, filling the living room with tiny floaty bits of silver foil like at the olympics opening ceremony and pebble-dashing the ceiling with spots of tar. I didn't let him loose on my stuff after that.
Job done. Took the random wires out of the bottom of the fuse box, bunged in the relay and I'm now a happy flasher! Cheers @snotty!