Severe voltmeter needle oscillations

I'm not an electrical expert but I would use a digital or analog voltmeter or even a test light and check the fuse box for power when the turn signals and wipers quit. Do the headlights work all the time? Does the engine die when turn signals quit? Finding where you have power and not when things quit and a wiring diagram gets you closer. Along jumper wire to the battery neg. to meter or light eliminates a ground problem there and you can check for bad grounds under load.