No headlights on '75 duster

[grades]

Hi all,
I am having an issue with my Duster, and I need to display my embarrassingly green knowledge of electrical systems.
Basically the headlights are not working, and I don't know why.
All the other lights seem fine, blinkers, etc. I just replaced the headlight switch a few months ago, so i dont think that is an issue.
Browsing around, people say "check the grounds" etc, and i have no idea what this means or where to look. I took a headlight out, turned the lights switch on, and plugged in my voltmeter into the 3 connectors in various formation, but nothing "happened" on the voltmeter. I plugged in a new headlight for good measure, but no go. I checked voltage at the high beam switch and the voltmeter read 12V. Nothing noticeable is unplugged anywhere.
Could anyone give me some idea of what to look for here? In layman's terms would be ideal, i apologize for my lack of any electrical knowledge here. I am willing to take a crash course tho, because I need to fix this.
Thanks!!

 

[67Dart273]

OK, first, the headlight power gets to the headlight switch separate from park/ tail, which comes from the tail fuse

Headlight power goes to the light switch from what is known as the "in harness splice" or "no1 splice" which is a permanent splice on the black ammeter wire under the dash and taped into the harness

The light switch has it's own breaker.

But check the "easy to get at" first

Easiest is the dimmer switch. With the headlight switch ON, TWO of the dimmer switch terminals should be hot, and when you switch from hi to lo or vice versa, the the dead terminal should become hot, and drop off one of the other two. The dimmer has power coming IN to one terminal, and power going OUT one one at a time of the remaining two

From there the high and low beam power goes through the bulkhead connector, and out to the lighting harness.

What do you have for a shop manual/ wiring diagrams?

 

[grades]

Hi, thanks for the reply. I have the chilton's manual and these diagrams:
http://www.mymopar.com/downloads/1975/75ValiantA.jpg
http://www.mymopar.com/downloads/1975/75ValiantB.jpg
But not too sure what to look for there.
Here's what i did today, i plugged the red (+) wire of my voltmeter to the + terminal of the battery, and the negative into the headlight plug which showed my 12 volts on 2 of the wires. I guess high and low beam. So that means that the ground is ok right?
This was with the headlight switch off.

I am not sure how to test the headlight switch terminals, because to turn it on the switch needs to be plugged in, and then i cant stick the voltmeter probes into it.. I hope i am making sense lol.

 

[67Dart273]

As I said START at the dimmer switch. It's easy to get to and is in the "middle" of the circuit. IF you have power at the switch, it is either the bulkhead connector, problems in the forward harness, or a socket grounding problem out at the headlights

If you do NOT have power at the dimmer, then move up to the light switch. You should be able to work it around upside down so you can back probe the connector

You don't need the switch in the dash. You can put the plunger back in with it hanging. Be sure when you are "moving things around" up there you have the battery ground disconnected for safety

HEADLIGHT SWITCH

Looking at the switch on diagram B,

Pink, middle right, is park/ tail power coming TO the gauge from the tail fuse. This also supplies power to the instrument lamp dimmer

The unused terminal at middle left is for park lights on older cars. On newer cars, the park and tail are both hooked to the tail terminal, so the park lights are on with headlights

Top left, Black, is main headlight power coming TO the switch from the "in harness" splice. This is UNfused, as the switch has a breaker built in for the headlights. This is headlight power ONLY, and not tail, park, or dash

Top right, yellow, is the dome light switch when you twist the knob to the left. This grounds the yellow wires and turns on the dome/ courtesy lamps

Middle, light green, is headlight power going OUT of the switch to the dimmer switch

Bottom left, yellow, goes off through bulkhead to park/ marker lights. Black from same terminal, goes to rear to tail lamps


Bottom right, tan, is the dimmer controlled dash light output going TO the instrument fuse in the panel. From there it goes to all dimmer controlled dash lights

DIMMER SWITCH

The wire coming down to the switch vertically, to the right terminal, is headlight power coming TO the switch. With the headlight switch on, this terminal should be HOT

Top left, red, goes off to the high beam indicator lamp, and through the bulkhead connector to the headlight harness and to high beams

Bottom left, Violet, goes through the bulkhead connector and to the headlight harness and to low beams

SOMEWHERE out near the front of the car, radiator support, there will be an wire or two coming to a ground eyelet hooked to the body. Remove that, scrape clean and reattach, preferably with a star ground washer and new hardware.

 

[Sport 360]

Probably the wire on the bulkhead, they are famous for that. Mine is doing it now, until I fix it for good this winter every time they stop working I just have to give the wire a little wiggle at the bulkhead and we're good to go.

 

[OwdKasd]

Nm

 

[BillGrissom]

Here's what i did today, i plugged the red (+) wire of my voltmeter to the + terminal of the battery, and the negative into the headlight plug which showed my 12 volts on 2 of the wires. I guess high and low beam. So that means that the ground is ok right?
This was with the headlight switch off.

You need to learn basic multimeter use (youtube, etc).

Normal use in voltage mode is to connect the black lead (-) to BATT- and the red lead (+) to whatever you want to know the voltage of (rel. to gnd).

The other basic is measuring resistance between 2 points. In your case, check gnd by measuring ohms from the headlight plug gnd terminal to BATT-. Should be <5 ohm.

Not sure what to make of the dV measurement you made. With the switch off, 2 of the 3 wires are floating.

Not sure why you are guessing which wires are low and high beam. The wiring diagram has a pictoral view of the headlamp connector and gives the color code.