If you recall a couple of posts back I was troubleshooting an intermittent 12 volt DC problem on Whacker’s boat.

1961 Drifter, Steel Hull, Single 4 cyl Chevy.

Well establishing a common ground between the engine and house battery systems did not eliminate the intermittent electrical problem. The engine continued to die. It would sound like I turned off the ignition switch. The engine did not bobble at all. It would just died. Sometimes the starter would engage but it would not fire. Sometimes the starter would not even engage. You know it’s kinda embarrassing when you tell someone you have the boat fixed only to have the problem return. So I was back troubleshooting the 12 volt DC ignition circuit.

In my last session I had skipped over testing the ignition switch … for no good reason really. Standard practice is to remove the wires from the switch and test for continuity and resistance across the terminals. Disconnecting the wires eliminates the current pathway through the wiring and the potential for reading the resistance of that pathway instead of through the switch. But the wires on this switch were soldered in so I would have to cut the wires to test it.

But I was at my wit end so I tried measuring the resistance between the terminals with the wires still connected.

Testing Ignition Switch Resistance

Wow. The resistance is 194.5 ohms.   It should be less than 0.03 ohms. If I wiggled the key a bit the resistance would jump up and down ranging from 1 ohm to infinity.  Hum.  This old switch is bad. Makes me wonder why the resistance through the wiring side of the circuit is so high. I am gonna have to ponder on that one. Seems there might be a secondary ignition solenoid on the engine. But that’s for another day.

Off to the parts house for a new switch.  In the mean time if you are interested in a detailed explanation of how 12 Volt DC circuitry works you might want to turn to The 12 Volt Bible for Boats.  It is one of the best sources for information I have found. While this book did not make me an expert it did significantly expand my understanding of 12 volt systems and how to troubleshoot them. I bet somewhere in there it says … Don’t neglect to test the ignition switch.

Oh well. Another Boating Lessons Learned.

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