Help with some wiring for 1968 Dodge Dart

Really there is no way to know.......without openin up the harness and checking.

I don't see how just one single pole relay could be used for headlights.

Understand "original:"

The light switch receives power from TWO sources. One comes from the tail fuse, and provides power ONLY for tail, park, and the dimmer control

The second source is tapped off the "welded splice" off the black ammeter lead up under the dash. This goes DIRECTLY to the light switch and powers ONLY headlights.

So with the light switch out, so power to the headlight "wire"

that wire then goes to the dimmer switch (floor) and selects high or low beam. These two wires, high and low, then go through the bulkhead connector, and run directly out to the headlights.

To properly support high low beam, the "normal" thing is to tap into the high and the low beam feed wires out in the engine bay, use those sources to trigger two relays and feed the output of those two relays to the high and the low beam lamps

If you do not have.......wander over to MyMopar and download a free factory service manual:

MyMopar - Mopar Forums & Information - MyMopar Tools/Reference

From the same page, you can find NON factory wiring diagrams, sometimes not complete, but sometimes easier to follow

Please read this MAD article:

Catalog

And while you are at it:

MadElectrical.com - Electrical Tech

They also have an article on headlight relays

Catalog

And member on here "Crackedback" has a relay kit he sells. If you can find the thread I believe there's a diagram for them

[FOR SALE] - Plug and play - Headlight Relay Kits