1975 Duster Potential Wiring Harness Issue

[John Mountain]

My 1975 Base Duster has had some electrical issues lately that can all be traced to the number 2 fuse on the fuse block. My turn signals don't work, radio doesn't work, windshield wipers don't work. Occasionally they will all start working for a minute or two then go out again.

First thing I did was get some new fuses and replace the number 2 fuse which didn't work, so I swapped it with other fuses to make sure it wasn't a fuse issue. Then I checked the connections on the back of the fuse box to make sure they were good, which they seemed to be.

I'm no expert, and my troubleshooting capabilities have about run out so I've come here for help. I'm really hoping it isn't an issue with a bad ground on the wiring harness because this is my daily driver and I really don't want to tear the dashboard apart.

If you guys have any suggestions, please let me know.

 

[Demonic]

What is your voltage across the fuse block? One side is a constant hot, the items you listed are on the switched side. Sounds like the ignition switch, but without voltage drop readings, it's a guessing game.

 

[moparmat2000]

Also dont forget that for most items, your cars sheetmetal is the ground return path. For example, where your wiper switch attaches the metal instrument cluster housing, and the fact that the cluster housing is screwed into the metal dash frame is its ground return. Ditto for the wiper motor. The hardware holding it onto the firewall is the ground return path.

However with what you mentioned that all these things work and then all stop working at the same time points to an ignition switch in the column going bad. See pic below, this is prob the part causing the issue.

 

[Mattax]

Demonic and Matt have covered the most likely possibility.

My turn signals don't work, radio doesn't work, windshield wipers don't work. Occasionally they will all start working for a minute or two then go out again.

Those three items only work when the key is switched to run or accessory.
Check your owners manual, or a 75 factory shop manual, because the wipers are probably not fused. At least on earlier cars, they have circuit breaker.
If so, then we can say what all have in common is they share the 'accessory'power wire coming out of the ignition switch.
That said, 1975 might have two accessory power wires.

Terms: Accessory is everything not required for running the engine.

I'm no expert, and my troubleshooting capabilities have about run out so I've come here for help. I'm really hoping it isn't an issue with a bad ground on the wiring harness because this is my daily driver and I really don't want to tear the dashboard apart.

On these particular items there is probably not a ground wrapped into the harness. Every year and model is different but generally grounds are either direct from the item to the chassis metal or a short wire to the chassis metal.

 

[67Dart273]

Good suggestions above. Get the fuse panel out and stretched down where you can access it. Measure voltage, under load across the two fuse clips. You should measure almost nothing, zero volts. If that seems OK, Check both clips to ground under load. Simply, determine where / when you are losing voltage

Examine the fuse clips for corrosion, heat damage, rust, etc, and look at the back, wiggle wires check connector tightness, and inspect for discoloration showing heat damage, etc.

 

[triumphman]

Realize your car being that old, like mine, you may want to consider checking all of your connections for corrosion. Especially the firewall block. Every connector had some corrosion when I pulled them. The high speed blower wire usually burns, as does the AMP meter wire. The amp meter is a fire hazard. Good luck.