Doesn't the headlight switch feed the dimmer? Otherwise the dash lights and parking lights would be on all the time.

Yes. The H.L. Switch actually controls 2 seperate circuits with 2 different power feeds. Black with white tracer wire (from main harness power in splice) switches to green power wire to Floor H.L. Dimmer switch. Power from dome lamp circuit runs to H.L. Switch (pink wire pigtailed to grey clock wire at back of switch) and powers the Parking Lamps. When you turn on Parking Lamps power flows through Switch to yellow wire to Dimmer Switch. Pic shows the Dome/ Cigar Lighter circuit removed from a '70 Coronet Dash Harness. Top Right you can see the fuse tap with red and pink wires. That's where power enters this circuit.

A wiring diagram would be much more helpful than a pic of loose wires.

That's why I have an FSM. Don't you?

It's a neat wiring harness you posted but it doesn't help the OP very much because it's hard to see where the wires would go. But a wiring diagram would. Why would I need a FSM for a car I don't own?

Well if you had the '70 Coronet FSM then you could have pointed out that I was wrong. Power to the dimmer switch does come through the H.L. Switch, but from the Stop and Tail Lamps fuse, not the Dome Lamp, as I had previously posted, and through a black wire pigtailed from the back of the H.L. Switch, other end pigtailed to a yellow w/ black tracer wire at back of Dimmer Switch. What's confusing about the FSM schematic is the multiple use of Pink Wires. Three different circuits use Pink as power wires, Parking Lamps- dimmable circuit, Windshield Wiper, and Brake- Dome Lamp( from the Hazard Flasher which also runs power to the Flasher Switch, opposite side of connector). And the Brake Lamps are on the Hazard Flasher fuse, not the Stop and Tail Lamps fuse.
The '70 Coronet FSM is not available for free download from MyMopar.com, and the schematic they have available pales in comparison to what's printed in the FSM.

Ask and ye shall receive.

I believe I said you were incorrect and didn't need a manual to figure it out.

That read like a question, so I answered it. Didn't recognize it as a cryptic remark on my response. My bad.
And I am correct- pink wire powers the parking lamps and dimmer switch.

My Dome lamp, map light, glove box, turn signals and bright lights indicator all work properly..

The only thing that doesn't work are the dash lights....

Did you try supplying power to the dash light fuse?

in your diagram - E1-18T Instrument Lamp (FEED) feeds the instrument panel fuse in the fuse block. The E2-18O (fused output)goes to the instrument panel lights. Both 18T (top of the fuse) reads 0 volts as does 18O) bottom of the fuse... when using the voltmeter...

My thinking is my dimmer switch is bad... as all other lights, Dome, door jam switches, turn signals and indicators on the dash, H/L headlamps. bright light indicator and map light all work...

From the diagram this implies that the H/L feed to the dimmer switch L7A-18BK is hot - otherwise no dome light etc...

What do you guys think?

No I haven't tried to supply power to the top of the instrument panel fuse... Guess that's my next test - doh!!

No I haven't tried to supply power to the top of the instrument panel fuse... Guess that's my next test - doh!!

Jump the dimmer and see if you get dash lights.

next car task on my list!

I installed the 5-LED Lights from O'Reilly's in the dash of my 84 D350. I installed four of the nine and stopped to check them out. They looked great. I continued on and installed the rest - and then they didn't work. I chased the problem for DAYS. My finding: They were polarity sensitive!!! I used my Power Probe to find the + and - of each bulb, then traced the circuitry of the dash insert for the + and - and installed the bulbs accordingly and then, they worked!!

Good Luck!

Rotate the dimmer wheel. I've had a couple with dead spots- you can clean the resistance coil and contact of the dimmer switch with 1000 grit sandpaper and some WD40- cheaper than buying a new switch. Be gentle though- the coil is fragile. If you need an expert, JS Restoration can restore your switch. Check the Hot Deals forum.

The reason for applying power to the fuse is that it feds the bulbs directly. If they don't light then check polarity. It takes the dimmer out of the equation.