Turn signal goes out at "high" load

I agree with Redfish. Plus, a modern voltage regulator may solve your problem too. The electronic voltage regulators do a much better job at keeping the alternator's output at 12.5 volts or higher, even if the engine's idle RPMs remain the same. If you already have an electronic VR, then check the ground contact on it and clean it up. If that doesn't work, raise your idle just a tad.

Oh and welcome to MOPAR's!