Headlight switch , is it the cause? or the curse?

Well you sound like you have WAY more troubles than the light switch.

Here's how the early switches work.

B1--B2. This is power in. One, B1 is UNFUSED power for ONLY the headlights, the other B2 is FUSED power coming from the tail fuse. This powers tail, park, and DASH lights

The headlight section is one separate switch, only for the headlights. Power feeds to the switch from the ammeter, a "nice big" wire, goes through the switch AND and internal breaker, and TO the DIMMER switch, where you select hi / low beam, then OUT through the bulkhead connector to the headlights.

There then, are several places for problems

"Rare" is the power source at the ammeter / harness connection but it does happen

More common is deteriorated contacts in the headlight switch connector

Bad switch, itself

Bad connections at the dimmer switch, or bad dimmer switch

Bad connections at the bulkhead connector......one for hi, one for lo beam

Bad GROUND connections at the headlights 'out at' the fender

Bad connections at the headlight connectors

YOU must go through each "point" in the system and find the troubles.

WHAT YOU NEED:

This is for troubleshooting, no exceptions, minimum, "must haves"

Some sort of multimeter

A 12V test lamp

A few alligator clip leads

And a factory service manual including the wiring diagram. You can download these free "for some years."

http://www.forabodiesonly.com/mopar/showthread.php?p=1970088617

And here

http://www.mymopar.com/index.php?pid=31

Also from "MyMopar" are aftermarket diagrams. These are NOT factory diagrams, are not always correct, and don't always show all connectors and options. They ARE however sometimes easier to follow and are at times very useful

66 Dart "MyMopar" diagram

http://www.mymopar.com/downloads/1966/66DartA.jpg

http://www.mymopar.com/downloads/1966/66DartB.jpg



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Here is how the tail / park / dash light stuff works

Look on the two diagrams, "A"

Look at the far left connection on the headlight switch, "IN" which is TAN. This is the OUTPUT of the switch for the dash lights. That circuit gets power off the TAIL circuit, goes through the switch, and OUT on the TAN. The TAN feeds dimmer controlled dash light power down to the fuse panel, to the INstrument fuse, and then out to all dimmer controlled lamps on ORANGE wires. THIS IS the only fuse that operates in this manner

The YELLOW wires coming off the switch at lower left are the DOME light switch. These are the grounding side of the dome light circuit, which goes to the door switches. The light switch, when twisted 'far left" grounds out that yellow to operate the dome lights

Yellow /Tr (yellow with tracer) coming off at far right and going off the page to the right is the PARK lights. These are ONLY on (in older cars) when park lights are on, NOT headlights. When "Ma" changed to 'full time" park lights in? 70? all she did was move the park light wire over to the TAIL light connection!!!

BLACK coming off the top of the switch is going to the TAIL lights.

It is far far better to check these switches "in operation" using VOLTAGE rather than ohms. It is difficult to RELIABLY check a switch with resistance. This is because of the heavy load on the contacts, which can change do to arcing, and so on.

Turn the switch on. Wiggle it. Wiggle the connector. Look for changes in brightness. Take a reading at B2, the tail light power, and another reading on the tail and park terminals and see if the reading is the same. You need to read down into tenths of volts