I’ve talked a bit on the unique wiring harness clips in part 1, so I’ll go into more detail with pics on the routing of the engine wiring harness throughout the engine. Starting from the fuse box plug in, the wiring comes up and over the brake booster where the first firewall attachment hook is located.
The separate brown wire is the tachometer wire. It is run from the unitized distributor to a firewall grommet that sits off to the right in the above picture.
That connection gets us over the brake booster and to our second firewall connection. This one sits just below the wiper motor and the first split off of wires that connect to the wiper motor.
Second firewall connection and first accessory connection coming from the harness.
The brown tac wire is also run through this connection. There is a single black wire in the above pic. Disregard that wire. It is not supposed to be there. That is the wire that comes from the intake TCS switch and goes down to the transmission. For some reason, that was cut and run separate at some point in the last 40 years. This wire should be with the two wires that stem off the wiring harness near the distributor and drops down to the transmission (See the pic below).
These two wires drop down to the transmission. One wire will be used on 4spd and both will be used for auto transmission.
From the second firewall connection, the harness splits. One side goes behind the distributor to a third firewall connection, and the bulk of the wires go along the topside of the drivers side valve cover, along the edge of the intake. At the front of the valve cover, there is another connection for the harness that attaches to the valve cover bolt (see part 1).
Here is where it rests along the topside of the valve cover.
There are a lot of wires that come out of the harness at this point. There are two wires that go to individual connections. As covered in part one, the green wire comes out and around the front of the valve cover and to the secondary temp switch on the cylinder head. The yellow wire with black stripe comes out and goes to the carb solenoid. These solenoids are often times missing and the yellow wire is just dangling somewhere at the end.
Yellow wire with black stripe connects to carb solenoid.
One bulk of wires goes down in front of the block and down to the starter. These wires are run close to the fuel line from the carb to the fuel pump.
Fuel line is on the left of the marker, wires are the right. Wires run down in front of the block and along side the water pump housing.
The second bulk of wires goto the alternator. See above pics. Now, back to where the wires first split after the second firewall connection. There is a short section of corrogated tubing that goes to the third firewall connection. At the end of the corrogated tubing, there is a split, where the two wires come out from the harness and lead to the transmission. The rest of the harness goes to the passenger side, and the wiring gets run through that third firewall connection.
Two wires split and drop to Trans then the rest goes through the firewall connection. The grommet on the firewall shows two lines exiting the firewall. One is the AC vacuum line with inline filter that goes to the carb tee. The other is the AC wiring harness. This harness is separate from the engine wiring harness and also goes through this third firewall connection.
From the third firewall connection behind the distributor, the harness curves around the distributor and goes to the passenger side valve cover and makes connection there at the rear valve cover bolt connector.
Here’s a good look at the third firewall connection showing both engine wiring harness and AC wiring harness (separate) both run through this connection. Again, please dismiss that black wire, it is not supposed to be there. Here, you can also see the inline fuse that goes to the tac connection on the unitized distributor.
Alright, now onto the passenger side of the engine harness. Whether or not your car has AC, you will have this next connection at the rear of the valve cover. If you do, it will look like the one pictured below and have a brown wire that goes out to the front of the engine and makes the rest of the connections to the AC accessories. This location is where the AC harnes plugs into. Again, if you do not have AC, then you will have an open plug sitting on the valve cover connection.
Top side A/C connection. This pic is also in part 1.
You can see in the above pic, this is where that black wire comes from that should be disregarded in previous pics. This black wire is supposed to be run in the wiring harness that goes back to the third firewall connection, then comes out as one of the two wires that lead to the transmission. This is part of the TCS system. I won’t go into specifics of that system here, but I will show you how it gets hooked up. These systems are almost always disabled, or missing. Now, coming from the third firewall connection, there are three splits off the main harness. One, as I stated above, goes to the valve cover for the AC connection, the second is a blue wire that drops down to the oil sender connection that sits on the oil filter housing. The third split off goes to that TCS switch that sits on the intake. The connection has a resistor built in the plug.
This is what the resistor looks like and is covered with black tape.
The rest of the engine harness goes to the water temperature switch on the passenger side. The harness goes through the lower valve cover clip and connects to the water temp switch.
Engine harness ends here at the water temp switch.
The engine harness ends at the water temp switch. Now, if your car has AC, the AC engine harness section will be added at that connection on the topside of the passenger valve cover and extend out to the AC accessories.
Here you see the single brown wire coming from the back of the valve cover and connecting to the thermal switch.
The brown wire runs along the topside of the valve cover and connects to the thermal switch. The switch is mounted on the underside of the forward AC intake bracket. From that switch, the green wire comes out and goes into a wire clip on the bracket. These are often missing and it sits to the right of the switch as you look at it from the front of the car. This wire goes to the compressor. There is a ground that comes off this connection that goes to the top mounting bolt of the compressor:
Compressor connection from thermal switch.
The black wire from the thermal switch goes to the back side of the compressor.
This is a single push on plug on the back of the compressor.
The Thermal switch looks like this:
Thermal switch that sits under the forward AC intake bracket.
There you have it, installation and routing of an original 455-HO engine wiring harness! Next up, correct engine vacuum routing.