I was going to change my engine wiring harness today with an M&H one and I ended up aborting the project as there seemed to be some additional plugs/wires on it. I pulled out the 1972 Duster wiring diagram and figured out what 2 of the wires were, but there is a plug in this harness that I can't figure out. It is the plug that you see on the middle of the photo, it is on the black wire that goes to the brake light warning switch plug, if you look at the bulkhead when mounted on the car it is the top left hand wire (drivers side top). Does anyone know what this connects to or what is what for? Another thing is that this car has A/C so there is one A/C wire that seems to be inside the tape of the part of the harness that goes to the alternator. I am assuming that I will just need to unwrap that side of the harness and take that wire out of there. Does anyone know if the A/C wire that goes to the compressor was taped along with all the other wires that go to the alternator or if it was originally outside of the engine wiring harness sitting by itself? This harness has been butchered a bit and I have no idea how it should be.
1972 Duster 340 M&H wiring harness
- Thread starter HSDemon
- Start date
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The AC clutch wire is a separate harness that plugs into 2 empty slots on one of the firewall connectors... usually the blower fan (green) wire is part of that harness too... that harness is available from Year One (M&H). Not sure about that plug... does it go to the firewall plug? If so tracking that down in the schematic may give a hint.
It could be a brake light test connector used for a diagnostic test. Go to mymopar and look at the 1973 service manual on page 8-155. It is near the bottom of the page and is labeled brake test.
Not sure why it's not shown in the 1972 service manual.
What's the part number of your M & H harness?
Not sure why it's not shown in the 1972 service manual.
What's the part number of your M & H harness?
Part number of the harness is 00695. Makes sense that it would be for a brake test.
I don't recall that mystery plug but our '72 harness did have a plug on the engine harness off the blue (hot) wire over by the carb like for an electric choke. I could not find evidence electric chokes were even a thing in '72... it was great it was there when the new Edelbrock when on it and an electric choke.
Here's a simple way to determine if that is a brake test connector. Use your ohm meter to run a continuity test.
Place one probe in the brake warning switch plug and the other probe in what could be the brake test plug.
Place one probe in the brake warning switch plug and the other probe in what could be the brake test plug.
That blue wire is on this harness too, it is for the idle stop solenoid that all 340 cars brought from the factory. My car no longer had the solenoid, but it does have a place where it mounts to the intake manifold, and the Thermoquad carb does have a place on it where the solenoid would contact it to set the idle speed. The blue wire has a clip that plugs to the accelerator cable bracket.
The brown wire that goes to the brake warning lamp switch is just cut about 2 1/2 inches from the bulkhead connector and a plug is installed there. I see no other explanation than it has something to do with testing that switch, but I cannot find that plug anywhere but in the 73 chassis service manual, which was pointed out by Townsend and where it does say that there is a test plug there. Interesting thing is that I looked all over the 72 and 73 service manual and there is no test in there where you would use that plug...
Don't recall my '72 Dart having this issue, maybe I missed something. There is a separate harness from the compressor to the drier? Two blue wires if I remember. Maybe both don't plug into the compressor, but it is a separate harness.
I finally installed the harness on Sunday and everything went well. The A/C wiring is just one wire that goes to the compressor. While doing some research on the 72 service manual I found that the wire going to the compressor should go first to a low pressure switch that goes on the drier. There is no low pressure switch on the drier of this car and the A/C wiring just goes straight to the compressor. So, I guess I now have to get a low pressure switch and put it on the drier and make all these wires longer... Oh the joy of working on these old cars 
Update on brake test connector. Had to find some old notes from the 20th century.
The connector was only used to test the brake warning lamp on the assembly line. It wasn't meant to be used after it left the plant, which is the reason it's not covered in the service manuals.
If you would like to duplicate the factory test, just take a wire and plug one end into the connector and ground the other end. This will turn on the brake warning lamp. Of course the ignition switch needs to be in the on position.
The connector was only used to test the brake warning lamp on the assembly line. It wasn't meant to be used after it left the plant, which is the reason it's not covered in the service manuals.
If you would like to duplicate the factory test, just take a wire and plug one end into the connector and ground the other end. This will turn on the brake warning lamp. Of course the ignition switch needs to be in the on position.
That is great info! You learn something new every day
Just went out and took two pictures, one is the drier, the other is where that A/C 2 wire harness, blue, one wire turns and goes over to the compressor, the other goes back towards the firewall. I didn't chase the wire down that goes back to the firewall, that harness is available from M & H.
Thanks that really helps, I had no idea where or how those wires were routed. Year one has the harness, little over $40 going to order one today.
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