I am ready to dive in deep and fix my dash cluster. I keep thinking it could be something real simple, like a missing ground.
Facts:
What does not work:
all gauges, all dash lights, all indicators, horn, radio, back up lights

What does work:
Lo beams, brake lights, turn signals, dome light, and car starts fine and runs.

Oddity:
Ammeter connections have been cut and wires have been tied together.
Hi Beams cause a short, still unsure where the short is.

Is there any test I can do with my Multimeter with the dash in vehicle? To test for ground? Walk me through.

p.s. there is a little ground wire off the steering column that is not connected. But it is literally 3 inches long. Has a loop ring to mount, but no idea where it should connect? I don't think that would effect the dash issue? or would it?

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66 dodge dart 270, 225ci, 3.7l, L6

For starters, the instrument cluster grounds through its mounting screws to the dashboard.

Ammeter bypass is a pretty common hack, but doesn't fully address the issue of sending alternator output through the firewall multi-connector.

That connector (big black square next to the master cylinder) is a good place to start - unplug it and clean all those connections.

Sounds like you are following someone else's attempts to fix it, which means a steep learning curve and difficult long-distance diagnosis. Who knows how many other wires have been cut/spliced/etc?

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O==\=/==O

"A mechanic is Somebody."
- Jim Preston

Check the HI/LO beam switch on the floor. They can cause some weird issues when they don't work correct;y.

Aside from bad grounding of gage cluster by its attachment screws, look closely for damaged pins that connect harness to circuit board, and or damaged copper strips on circuit board.

You can use a 9v dry-cell battery to test temperature and fuel gage function. Make up a little set of jumper wires to connect 9v battery to gage and see if it responds. Don't keep the battery connected any longer than necessary or you may cause a melt down. Also check the main feed wire to gage cluster, it may be cut, burnt up, or disconnected somewhere along its path.

By the way, what vehicle and year are we talking about here; 66 dart?

Wire diagram here.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

yes 66 Dart. Ok lame questions, but if the cluster board is grounded to the dash via the connection screws, what is the dash grounded to?where is it grounded?
also good info on Hi Lo button, but I already replaced it, and new connector, still shorts out when Hi beam is pressed.

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66 dodge dart 270, 225ci, 3.7l, L6

Typically the dash has screws that mount it to the firewall (sometimes hidden by the windshield gasket or sealant depending on the model).
There are also 2 mounting bolts on each side on the bottom of the dash near the door jambs (may be hidden by the kickpanels if so equipped).

Ground strap at the steering column can connect under one of the studs that hold the steering column to the dashboard assembly...(pull cover plate where column and underside of dash lip meet).