SC cut-off switch

JB · 03-03-2004, 12:34 PM

Can anyone give me some guidence on wiring in a PCA Club race approved cut-off switch in a stock '82 911SC? I have a Sparco switch with 2 main terminals, 2 normally open terminals, and two normally closed terminals. They provide a 3 ohm resistor to drain off voltage to ground to prevent run-on current from the alternator. There are three smaller red wires going to the battery now as well as a larger cable running back to the starter. I must be missing something simple but am having trouble getting it to work.

Thanks!

JB

Cosi1 · 03-03-2004, 04:14 PM

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78targa · 78targa's Garage

JB,

I put one in a couple of months ago. I think you have the same type you do. Give me a call if you want and I'll try to walk you through how it is supposed to be wired. It is 9 PM here, but you can call up to 11. I'll be gone this weekend at a club race, so tonight is the night I can help.

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304065 · 05:43 AM

All right, good question!

You are SMART to get the six-pole switch so's you don't trash your alternator. Be careful, however, if you have any sensitive electronics like video cameras connected to the main bus-- when you throw the switch the voltage WILL spike off the scale for a second until the resistor takes up the load and shorts it to ground.

This original procedure from the NNJR PCA web site, with edits by me.

Remove the battery ground, then disconnect the positive battery cable from the starter. This will be connected to one of the large terminals on the switch. Find the smaller auxiliary lead on the positive battery cable near the battery terminal and cut it off close to the cable. This lead will be connected to the second large terminal of the switch. Attach another battery cable to this second terminal and run this cable to the starter. Most auto parts stores will make this cable up for you, just let them know how long you need it and what size studs each end attaches to. Also, from the same terminal, run a 12 gauge wire to one of the terminals marked "1" on the bottom of the switch. The two terminals marked "1" are the Normally Open contacts of the switch. The other "1" terminal will be connected to the supplied resistor. [The "1" terminal is the normally open pair- JC] The other side of this resistor is connected to a good ground. This resistor is what protects your alternator diodes. The resistor should be tie wrapped to the other wires and the leads insulated. You have now succeeded in disconnecting your battery and protecting your alternator, now for shutting off your motor. There are two terminals left on the switch, these are marked "2". These terminals are for the Normally Closed contacts of the switch. Disconnect the wire going to the "+" terminal of your ignition coil and attach this to one of the terminals marked "2". Run a 12 gauge wire from the remaining "2" terminal to the ignition coil "+" terminal. Now all that is left to do is to mount the switch and reconnect your battery ground cable.

You might want to verify with an ohmmeter or test light that the "1" terminals are NO, and the "2" terminals are NC. The procedure as written on NNJR web site had them backward.

Good luck!