1973 Duster Electrical Issue

My suggestion is to track down the problem(s) in sequence.
You can do some of this without any tools.
(A battery charger and a multimeter will be helpful if you have them but htis will get you started.)

Using the ammeter
The ammeter will indicate electricity flowing out of the battery. Needle up is none. Needle fully toward D is about 40 amps. (30 to 40 amps either way is danger zone)
With the key off, the ammeter should indicate zero until something is turned on. Then is should move.

For example:
If a lamp is turned on and the needle moves a little, it is indicating current flowing out of the battery and through the bulb.
If the switch is on and the needle moves, but the lamp doesn't turn on, then there is short circuit afte the switch. Current is flowing out of the battery but its not getting to that lamp.

In this situation the ammeter probably won't be a big help, but is worth checking because it can flag things that otherwise would be head scratchers.

A Method to Narrow Down the Problem

1. Check all the devices that should work with the key off.
Brake lights (brake pedal)
Headlight switch.
Both Feeds should work. Parking, tail and instrument feed is fused. Headlight power feed is not (circuit breaker is in the switch).
Hazzard lights (emergency flashers) If these all work, then the fuse is good.
Horn
Dome light

Check the fuses if they don't work. If you have a voltmeter or test light, check for power to those fuses.

Check the items that shouldn't work with the key off. If any of them due, then there is a cross wire short.

2. Key in accessory position
Check the items in sequence in the feed to the flashers
Heater fan, radio, backup lights, then flasher.
( Note that we've has a couple of members recently find the backup lamp cable shorted on the transmission case. )

Wipers work. So we know the switch accessory circuit is good, at least to the wiper switch.


Knowing more about which ones work and which don't, and the bulbs and fuses are OK (or not) then can get into the turn signal/brake wiring along with ht egrounding of the two filament lamps.

I'll post some links about how to trouble shoot those.