The two systems are more compatible than you might think. The switch had 4 terminals that looked like the basic switch, plus another plug that connected to the optional harness. Immediately after the gages there is a single lamp 2 wires for the heater controls and a single lamp 1 gray wire for the side gauge cluster. Different engine harnesses There were variations in the engine harness to allow for the many engines in the Firebird lineup. Most of our cars are 1977-81 vintage, and these cars tend to be highly optioned.
You may notice the wiring looks really fat; that's because there is a big rubber hose bound up with the wires. The 3 plugs on the right would have plugged into the stereo. The plug nearby with red and green is for the backup lights. Here are the fuse block and cross-body conduit actually on the car, showing how the optional wiring runs up to the cross body conduit. The compressor circuit circuit runs through a pressure and temperature switches before continuing to the compressor harness.
It looks like one piece, and it is held to the fuse block by a bolt right in the middle See B in the firewall photo below. This is the Pontiac version. It plugs into a wire coming off the back of the radio plug see the radios section below. Arrangement of Wiring Through the Firewall Shown below is a car with the maximum number 5 of wiring harnesses coming through the firewall. You can see how three of the components shake out in this nasty photo. These extensions adapt the harness for different engines and control heads. .
This extension is for Pontiac engines, which had their alternators on the driver's side. First is an extra idiot light next to the fuel gage two wires, I think it's an electric choke lamp. It has a built-in piggyback jumper so it doesn't bogart the whole terminal. Our 1979 junk cars don't have a hint of a hole at C. On the passenger's side, it is routed over the glove compartment in a special wiring tray on the back of the dash pad.
This plug is black and it's obscured in the photo. This was minor compared to what happened next. The installed solenoid is shown at right. They also used a toggle switch to dim the turbo boost lights on the hood. The cruise control harness gets its power from the spare ignition terminal on the fuse block.
In mid year 1977, the switch was changed. The old switch had three blades on the passenger side and one on the driver's side. The electronics to accomplish the delay were all housed in the wiper motor. The 1978 plugs looked the same, and they were wired to play the right front channel and the left rear. On this car, smaller harnesses for the optional interior lamp group and a power antenna are both stuffed in there under the main I.
It is powered from the courtesy lamp harness, as discussed above. Some omitted the fuse, some had built-in jumpers as shown below on the power supply to the pulse wipers , and there was a combined cruise control and tach wiring harness with only one power supply. The single wire parallel to the rear body harness is going to the driver's seat belt. Pontiac called this the front body harness, but I find that confusing, so on this page I'll call it the middle body harness. In the photo, courtesy lamps are shown on the left and right ends of the harness. Optional power antenna and interior lamp group harnesses are installed. The 1980 fuse block was totally different and used blade-type fuses.
After the pace cars were built, the audio booster was generally available on any Firebird. The photo shows the inside part of the harness to the left of the grommet, and the under-hood part to the right. The long orange wire is a power supply from the spare battery terminal on the fuse box. Tach and main gauge cluster wiring are pretty obvious. This illustration is really intended to show the plugs in the main I.