Chev alternator and master switch wiring

On Mon, 12 Apr 2004 00:29:33 -0300, "Bill" wrote:

||Hi, ||I have forgotten how to correctly wire up my son's Chevy V-8 HEI derby car ||so it still charges, as required by rules, but it also has to have a working ||master switch too. ||I have Push To Start, and a two terminal master kill. ||Could you please direct me to a wiring diagram to do this right? I searched ||the net but couldn't wade my way to anything helpful. ||Or a plainly written, step by step instruction set, would be ok too.

For an alternator car, you normally need a 6-terminal master kill switch.

2 big battery terminals, and 4 spade terminals for the alternator side.

The following was sent to me in answer to the same question. Author is unknown, but the last part is from Bob Clark of Pegasus Racing Equipment.

WIRING YOUR MASTER SWITCH (for cars with alternators) This master switch must kill all power except for an electrically operated fire system, if so equipped. This switch must also shut the motor off, which means that you will need a 6 pole switch, not a 2 pole. If a 2 pole is used, two things will happen:

1) The car will keep running because of residual magnetism in the alternator, which will keep the alternator supplying power, and 2) The field being disconnected on the alternator will cause the smoke to leak out of your diodes, (and since we all know that electronics runs on smoke, the depletion of this smoke will render the alternator inoperative). The mounting location for this switch is just in front of the windshield on either side of the car, below the center of the rear window, or mounted on a bracket attached to the roll cage (with the bracket welded or clamped to the bar, no bolts into the cage) in a position easily accessible from the open window. Don't forget your "OFF" decal. The easiest way to wire an OMP 6 Pole switch, (available at Driving Impressions), on most cars is as follows: 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 Closed contacts of the switch. The other "1" terminal will be connected to the supplied resistor. 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 Open 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. After installing, start the car and run it for at least 10 minutes (it takes some time for the alternator to build up enough of a magnetic field), then make sure the switch will shut it off. With the switch off, check to make sure that the car will not crank, the fuel pump, wipers, and all lights will not operate. Go from the battery to one side of the switch. Go from the other side of the switch to the fuse box. Take the alternator output to the battery side of the switch.

from Bob Calrk: This is pretty easy.Do not be intiminated by the directions. The big terminals are for the battery cable. on the four terminals it works like this.When the key is ON two of the terminals are closed and two terminals are open. When the switch is OFF the terminals flip flop and the one that was closed is now open and vice versa.Now to hook it up. Use an ohm meter and find out which two terminals are closed when the switch is on and take the wire from the + side of the coil and run it to one of the terminals you found above and run a wire from the the other terminal from above to the + side of the coil.On the other two terminals that are closed with the switch OFF run the resister that came with the switch to one of these terminals with the other end of the resister to ground.Next take a short wire from the other terminal to the big lug where the battery cable is on the switch. Go to the cable going to the car not to the battery.

Hoe this helps

Rex in Fort Worth

I guess I need a new switch then. I have no idea what the resister to ground-when switch is off is supposed to do, otherwise it make sense. Thanks.

Simplistically, the resistor forces the alternator to stop trying to charge nothing, which is what causes the big voltage spike and burns out the diodes.

Ok now it's all clear, though I've never seen that done in these parts. Thanks again.

||> >

||> > I guess I need a new switch then. I have no idea what the resister to ||> > ground-when switch is off is supposed to do, otherwise it make sense.

The resistor is a "bumper" to absorb the surge of power when you suddenly chop the circuit. Keeps the alternator diodes from popping. Rex in Fort Worth

So you run alt to ground through a resistor to discharge the alternator after the fields are cut? There is no more "new" voltage feeding the alternator so the controlled short through the resistors has nothing more to short out and it stops charging an d doesn't keep producing 'new' voltage that would otherwise keep feeding the ign system? If that sounds correct I guess I get it?