19. Wiring

19.1. Neutral Sensing Harness

The neutral sensing harness is no longer used. Tie-wrap the harness and tuck it under the dash. By leaving the harness unplugged, the computer “thinks” the transmission is in gear, which is essential for proper function of the EGR valve.

19.2. Reverse Lamp Extension Harness

The plug that used to connect to the reverse lamp switch on the steering column mates to the extension harness used in 1978-1981 manual transmission cars (Figure 19-1). Since my Monte Carlo SS was originally equipped with a floor shifter, it already had a round hole in the floor for the shifter cable. This hole was a bit too large for the reverse lamp extension harness grommet, so I made a small sheet metal patch with the correct size hole and screwed it to the floor over the shifter cable hole.

Figure 19-1: Reverse Lamp Extension Harness

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My 1983 Malibu Wagon had a column shifter, so I routed the reverse lamp extension harness through a hole I made in the firewall in the factory location for 1978-1981 A body cars with a manual transmission (Figure 19-2). Note that the firewall insulation is precut by the factory. I recommend this technique rather than the one I used on my Monte Carlo SS.

Figure 19-2: Alternate Route for Reverse Lamp and Cruise Control Harness Recommended

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1981 A body cars used a WEATHERPAK® connector at the reverse lamp switch. 1978-1980 A body cars used the round-shaped connector shown in Figure 19-1. A similar harness should be obtainable from other GM manual transmission vehicles or can be made from an assortment of donor cars. Bob Morris assembled his reverse lamp harness using the wires and firewall grommet from an early 1980s Chevrolet full-size pickup truck (very long leads), a locking plug, for underneath the dashboard, from a Chevrolet S-10 pickup truck, and a GM plug and pigtail to mate to the reverse lamp switch on his T56.

19.3. Cruise Control Harness

Both of my cars have cruise control, and I wanted to retain it, therefore, the cruise control harness had to be rerouted. I recommend rerouting the harness as shown in Figure 19-2, though lengthening of the harness is required. Rerouting the harness as shown in Figure 19-3 does not require lengthening the harness, but the routing is not as clean as the recommended route.

Figure 19-3: Alternate Route for Cruise Control Harness – Not Recommended

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19.4. Torque Converter Clutch Harness

Pull the TCC harness up into the engine compartment and drape it across the air conditioner/heater box. Be sure to tuck the plug away somewhere will it will not be seen. Strategically placed, the harness will look like it belongs there. In my 1983 Malibu Wagon, the harness was long enough to drop the plug between the fender and the air conditioner/heater box. In my 1986 Monte Carlo SS, the harness was not as long, so I draped it across the top of the air conditioner/heater box and tucked the plug in between the air conditioner/heater box and the evaporator dryer.

19.5. Neutral Start Switch

The neutral start switch should be connected in series with the 12-gauge purple wire coming from the ignition switch. The 1978-1981 GM A body neutral start switch (Figure 19-4) had only one set of terminals, which produce a closed circuit when the pedal is fully depressed. Note that some replacement neutral start switches (Figure 19-5) have two sets of terminals. One set produces a closed circuit when the pedal is depressed and the other set produces a closed circuit when the pedal is at the top of its travel. Be sure to use the correct set of terminals when using a replacement neutral start switch.

Figure 19-4: Original 1978-1981 GM A Body Neutral Start Switch

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Figure 19-5: Replacement Neutral Start Switch

Photograph courtesy of Bob Morris


Originally Released 11 February 2002

updated 27 August 2007