Why do signal lights both flash without 4ways on

I assume you mean they flash in all four corners when you turn on the turn signal. If that is right, check the trailer wiring harness to see if the wires are chewed up and touching.

Also check if the 4-way flashers are non-functional but the switch is turned on. That will connect the two sides together electrically.

You didn't mention anything about the head lights. If you have multiple lighting circuits involved in this problem, check if they're all dimmer than normal. A bad ground will cause the current through one bulb to seek an alternate path to ground, and that is through another bulb(s), but since the voltage splits among them, none will be full brightness.

You didn't say if the lights are dim or full brightness. If a ground wire is the problem, you can prove that by removing one bulb. If that causes any other bulb to go off, it's a ground problem. You can also remove all the affected bulbs but one, then check if that one works right. If it turns on with the wrong switches, there is a different wiring problem. Most commonly two wires are touching such as the trailer wires I mentioned. An aftermarket radio that is wired wrong can do that too. There's a wire to it for the tail lights and one from the dash lights.

What gremlin did you find?

Dandy! Happy to hear it's solved.