Diagnose, don’t assume, when problems arise

Sometimes when working on your engine, it can be very tempting to jump to conclusions without properly and completely diagnosing the problem.

I was recently reminded of this while working on a customer’s engine. The boat was brought into the shop because the starter was not working. I located and bypassed the starter solenoid by jumping across the two large terminals. The starter immediately cranked the engine.

I then jumped the small terminal lead on the solenoid in order to energize the solenoid, and the starter again cranked the engine. The obvious conclusion was either the key switch or the neutral safety switch in the control box was defective. I started to reach for my tools to remove and disassemble the control box when a little voice inside warned me to slow down and thoroughly diagnose this problem.

I took out my 12-volt test light, jumper wire and volt/ohm meter. Starting at the key switch, I probed the wires and verified there was voltage going into the key switch and when the key was turned it had 12 volts going out. The key switch was good.

This boat had a huge mass of wires under the dashboard that resembled an explosion in a spaghetti factory. It took several minutes to cut loose approximately a dozen tie wraps and uncoil all of this wiring. There were several connectors in these wires, and any one of them could cause a loss of power from the key switch to the starter.

I probed the wires on each side of the connectors to verify that power was traveling through the connector, and one by one eliminated each connector as a problem. When I finally reached the control box, and all of my tests had been positive, I was once again tempted to rip open that control and replace the neutral safety switch, but I made one last test. I checked the wire that comes out of the neutral safety switch and sends the signal to the solenoid. This wire also tested OK.

It was time to stop and think. The starter was working. The solenoid was OK, and both the key switch and neutral safety switches were also good. There was only one thing left, the main wire harness from the dashboard to the engine. I figured the most likely spot for this problem was the plug in where the boat harness is plugged into the engine harness.

It took some time to strip back the several layers of electrical tape from the harnesses, and here was the moment of truth. I probed the main boat harness, and found that I indeed had 12 volts traveling from the neutral safety switch through the main harness to the plug-in connector. I then probed the engine side of the connector, and to my surprise, I had a perfect 12 volt reading there also.

There was less than 6 inches of wire from the harness plug to the starter solenoid, and everything was in good working order. I’m not sure if it was curiosity or frustration that drove me on.

I began stripping back the layers of tape from the remaining section of engine-wire harness. I just knew I was going to find a broken wire somewhere in that last few inches of harness. There was no break in the wire. The wire branched off and doubled back toward the front of the engine.

Down under the bottom carburetor near the shift shaft lever I discovered something I have never encountered before. This engine was equipped with a second neutral safety switch attached to the shift shaft lever. This second neutral safety switch was bad, and it would not allow the starter solenoid to engage when the key switch was activated.

I researched the engine model and serial numbers, and discovered that this engine was originally produced with a tiller handle. It was not intended to have steering and controls. The neutral safety switch was installed on the engine in order to prevent the operator from accidently starting the engine while it was in gear. The person who converted this engine from tiller steering to a console steering and remote controls neglected to eliminate the extra neutral safety switch on the engine.

That second switch worked for many years with no apparent side effects, until that last trip when the engine would not start. It was only through a systematic step-by-step test procedure that I was able to find this mystery switch. Once discovered, it was a simple task to disconnect and remove the switch from the engine.

Thorough diagnosis may take a little longer, but it may also save you from making the costly mistake of replacing parts that are not defective. Generally, once you install parts on your engine, you cannot return them for credit. Not only are you out the cost of the part that was not defective, but you are also out the time it took to replace it, and you still do not have your engine repaired.

A little secret that can help you properly diagnose engine problems is to invest in a good engine service manual. Check with your local dealer, but the cost is usually under $50, and the information inside is invaluable.

If you have any questions about your boat, motor or trailer, e-mail me at theboatdr@yahoo.com.

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