I know this is a pain but please understand that there is nothing fundamentally complex with the simple 12 volt wiring of these old beasts.
indicators, radio and reversing lights...
OK, this is gonna sound dumb but if you drive it without the radio on and without reversing (or remove the reverse globes) ...
or for that matter, you don't even need to drive it, have the ignition on and play with the blinkers for 5 minutes, both sides.
If that is ok, then do the others, one at a time.
Then start 2 at a time, finally 3 at a time.
This will tell us if your problem is ground or short related or an overload on the fuse.
I would also put individual fuses on all 3 wires to further pinpoint the problem...