Electrical issues.

My 64 Dart is doing strange things. If I turn on the headlights everything works perfectly including the high beams when you press the dimmer switch, including the indicator on the dash. Turn the key on and the turn signals work perfectly, right and left front and rear and the indicator lights on the dash work correctly as well. with the key on, turn on the left or right signal and it works fine until you turn on the headlights. with the headlights on, all the exterior lights work correctly but both turn signal indicators in the dash will flash and the high beam indicator also will flash. If you hit the dimmer switch, and turn on the left signal the right indicator light on the will flash, and if you put the right signal on. the left indicator will flash, but all the outside light work correctly. Checked all the grounds, traced the wires under the dash and hood. Can't find anything that looks wrong. Used multi-meter to check voltages and found nothing. This issue just started and I don't know why. Replaced headlight switch, dimmer switch and flasher. Can anybody help me? Please.