high beams

WHICH SIDE of the firewall are you testing it on?

If you are testing it on the engine side, then it's "right there" in the bulkhead connector.

If you are testing it on the interior side, there is only "two feet" of wire between the dimmer and the bulkhead connector. "It's one wire." It has to be

the connection at the dimmer

the connection at the firewall

or a break in the wire.