# Diodes in V-twin Magneto Kill Wire Circuits



## Bob Driver (Nov 1, 2017)

Briggs puts diodes in the magneto kill wire circuits of their v-twins. The purpose is to protect the magnetos from shorting out each other, if one goes bad, and the possibility of a bad key switch (12v power applied to the M terminal of the key switch). On the Vanguard V-twins, you can buy the "diode wire" as a stand alone part -- Part#:844547, runs about $12 retail. On Intek V-twins, you usually have to buy the complete engine wiring harness to replace the bad diode(s). They run about $25 retail. I use 1n4007 diodes (1A, 1,000 peak volts). A pack of 100 is around $5 on E-bay, or Amazon. Using two of these, a soldering iron, and heat shrink.... drops the parts cost on the repair to about a dime. Part#:844547 for the Vanguard can be modified to work on the Intek V-twins, but the time involved is about the same as the "solder job".


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## wjjones (May 28, 2010)

Thankyou for the info Bob it will be useful.


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## FredM (Nov 18, 2015)

That is would be the way I would go too Bob, I would be repairing my own wiring loom also.


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## Bob Driver (Nov 1, 2017)

These diodes are tiny and you have know which way the bias runs. You may have to use a magnifying glass if you're an old fart like me, but diodes usually have a wide colored "Band" on one end of the body. That band tells which way the bias runs. The design of this wire is to protect the coils from each other or 12v being applied to the M terminal by a faulty key switch. In this case, the band goes towards the magneto end. If you're testing it with a VOM, ground lead on the magneto side, positive toward the key side -- continuity. A good reading appears to be about 5 Ohms. Usually, if only one of the diodes is bad, it's caused by a bad magneto. If both diodes are fried, 12V somehow came up from the M terminal of the switch. Two most common reasons - 1) Bad switch, 2) Battery hooked up backwards.....

I seem to do a lot of wiring repairs on my customers machines and I hate to butcher up the factory wiring, especially at the connectors. Here's the tool you need to take the pins/spades out of most any factory connector to maintain the integrity of the wiring harness. They run $5-6 on Amazon


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