Check the voltage with either the engine running or a battery charger on it. Just key on will have too low voltages, and the system will not work correctly. You must have full voltage. Also remember that the voltage drops .7 volts across each bulb, and .7 volts across each SCR in the dynamite sticks, so by the time the outer bulb lights, the voltage is down, so a dim result. Proper, slower flasher too. Many alternatives there as well.
There are many threads on this subject, and a few of us who know these systems. (I am one). Do the research.
Proper voltage and grounds, clean solid connections, followed by an oxidized/worn turn signal switch are usually the culprits.
Dan