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Old 05-01-2003, 01:41 PM
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Post Remote Shut Off Switch doesn't shut it off!

I feel stupid to even be writting this, but here goes! NHRA requires a master shut-off switch mounted on the rear of the vehicle when the battery is relocated to the rear of the vehicle. I have routed the very heavy battery cable from the battery to the new master switch and from the second pole of the switch to the starter lead. I have also attached the alternator output wire to the battery side of the switch. The pickup for the master power to the fused wiring block is from the second pole of the switch.
With the master switch in the "off" position, there is no power to anything, not to the coil, the msd box etc. But when the car is running in the master switch "on" position and the master switch is then turned "off", power continues in the system and the engine continues to run. I have checked the switch with and ohm meeter and I believe it is OK. I assume the power has to be coming from the alternator, but how (since it is isolated from the power circuit by the master switch when in the "off" position)?

I know this question is on the Mensa exam, but help me with some ideas if you can. Thanx.

Tom

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Old 05-01-2003, 03:23 PM
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[quote]I have also attached the alternator output wire to the battery side of the switch.<hr></blockquote>

There is your problem, reroute to the other side of the switch.
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Old 05-01-2003, 04:01 PM
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OK guys, I got a tip on another board. Here is what was happening: It turns out that the voltage gauge or idiot light wire (brown) from GM internal regulated alternator supplies a small amount of current, enough to supply power to the MSD unit. The MSD kit includes a diode which I soldered into this line and the problem is solved. The diode will not allow power to reverse in the line and therefore isolates the MSD from receiving power from the sensor circuit.
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