I have a 1977 Omega which currently has no turn signals. With the original flasher the left signal worked properly at all times and right was very weak with the headlights off, and with the headlights on had to be flashed manually. When the headlights were on the right signal also flashed the left brake light. Fast forward several months, and the flasher seems to have gone out completely. I replaced it with one I got at Autozone for $7, and now with the headlights off all signals flash and I'm having problems similar to the old one with the headlights on. At some point someone tried to install an aftermarket radio and the wiring under the dash is... interesting. I'd really like some input on this before I try a new flasher or, worse yet, take it to a mechanic.

 

Nine chances out of 10, or maybe even 99 out of 100, your problem is a bad ground somewhere. As cliche as it is to say, check all wiring. The right side flashing weakly while the left side was ok before the flasher gave out suggests a poor ground somewhere in the right side wiring.

Time to start tracing.