Installation of the Kill Switch and heater backdate for the 911

This weekend I finished the install of the kill switch and the heater backdate for my 911.  When it was all said and done, the kill switch was made out to be a lot harder than it was since none of the instructions online seem to have been made for a car that wasn’t a purpose-built track car.  What I had to do was use the set of connections that was marked ignition switch and power to coil or ecu, I used for the fuel pump.  The picture below is how I wired up the kill switch.

The wire for the power to the fuel pump is located at the fuse panel in the trunk and is red with a green stripe (at least in the ’84 911). I removed it from the fuse and extended to the kill switch, then fed a wire back to the fuse from the kill switch.  The power wires that were connected to the battery all had to be modified.  I purchased a new batter cable 3/8″ ring terminal and used that to connect the wires to the kill switch power stud.  The smaller wires that were attached the battery, I did the same thing to except used a ring terminal that was meant for the higher gauge wires.

And since no one really explains how the kill switch works, I’ll give a quick run down.  When the switch is in the ‘on’ position there is power flowing from the battery to the electrical connection on the other side of the switch.  The set of spade terminals 2 make a circuit and the other set of terminals are an open circuit.  When the switch is turned to the ‘off’ position, power is cut from the battery, the terminals marked 2 become an open circuit and 1 makes a circuit.  The set of spade terminals 1 is called an Alternator protection circuit, so when the engine stops running the voltage won’t surge back into the alternator and fry it, instead it will go through the resistor to ground.  The circuit made with ‘2’ must be something that when power is cut, the engine will stop running.  I chose the fuel pump as stated earlier since all the wires were right there.  However, now that I think about it, I probably could have done the same thing with the ECU’s power cable.

The second project I took on this weekend was the backdating of the heater in the engine bay.  Earlier 911s lacked the large blower motor in the engine bay to push air over the heat exchangers to the cabin.  However, my heat has always been pretty crappy and I live in Texas.  Heat isn’t super important, but it is nice to have.  So the pluses outweighed the minuses in my mind and I decided to do it.  Removing the heater blower motor was a pretty simple job, but if you have large hands it could be kind of hard since the screws and nuts are in some awkward places.  Once the blower motor and the associated tubing are removed, the backdate heater duct can go on.  You’ll probably want a hammer or mallet to persuade the piece to fit around the distributor.

I installed the piece, saw where it was going to be interfering with the distributor and took a hammer to it to make it fit.  Once I did that a few times, I put it back into the engine bay, screwed and it in.  I think cut some high-temp silicon hose that was 2.5″ diameter and forced it over the output of the piece then rammed the other side of the tube into the input for the heat exchanger and clamped it down with the clamps on the heat exchanger input side.

A close-up of the finished product.

The full, somewhat cleaner looking engine bay

Now that all of this is complete, I’m beginning my week-long project of Liquid Wrenching the exhaust nuts in order to install the headers onto my vehicle in the coming week or two.

Leave a Reply

Your email address will not be published. Required fields are marked *