POWERBOATER’S GUIDE TO ELECTRICAL SYSTEMS So, if the amperage specifications aren’t available from the engine maker, how do we get them? Easy! Just do a current-draw test when you know your starter is working normally and record the amperage the starter motor uses in your manual. Then when a problem does crop up, you’ll have a known value to work with as a benchmark. To do the current-draw test, first make sure your starting battery is in good, serviceable condition. If you have an inductive-clamp multimeter capable of measuring up to about 500 amps, clamp the inductive pickup over the main battery cable going to the starter motor and take a reading while a helper cranks the engine. Now you have the normal amperage you can expect your starter motor to draw. If you don’t have an inductive-pickup multimeter, one of the inexpensive Snap-On inductive meters shown in my tool collection in chapter 1 will do the job. When you have a starting problem that you think might be caused by the starter motor, first doublecheck your battery to make sure it’s charged and in good condition, then repeat the current-draw test. If your new reading is lower than the previously established benchmark reading, the starting problem is probably due to loose or corroded terminals in the battery cable connected to the starter motor. If the cable has been replaced since you established your benchmark and the terminals are clean and tight, the new cable is probably undersized and needs to be upgraded. If the reading you get is higher than the benchmark reading, make sure that the problem is not caused by a mechanical fault such as a partially seized engine or a frozen drive unit. You may need to call in a pro to help out at this point. Once you’re certain that the engine is not causing the problem, you can be sure that any excess current drawn by the starter motor is due to a fault within the motor. Remove it and send it out for overhaul.
Voltage-Drop Test Another useful test for your starter motor and starter circuit is to trace the circuit while checking for voltage drop at various points. This test will be outlined in the following section on outboardengine starter circuits and will work just as well for inboard engines. 128
Outboard-Engine Starter Circuits A system overview of a typical starter-motor circuit on an outboard engine with remote control is shown in figure 8-6a on page 129. On many engines the remote-control harness plug is located under the engine cowl, so this plug is not as shown in the diagram. If your outboard engine doesn’t have a remote ignition switch, it will have a starter button located on the engine, and may have a neutral-safety switch integrated into the mechanical shift linkage under the cowl. A simplified wiring diagram of this circuit is shown in figure 8-6b on page 129. Your engine may have some of these connections in a wiring junction box. Also, starter-motor battery terminals are often used by manufacturers as handy places to attach additional circuits, so refer to your wiring diagram and narrow the number of wires down to what you see in this drawing; ignore the rest. All outboard engines use inertia-type starter motors that engage the flywheel ring-gear when centrifugal force throws the drive gear upward. Medium-to-large outboard engines also use a remotely mounted solenoid just like those used on inboard engines. Problems with inertia systems can be as simple as a low battery, or corroded terminals causing a cranking speed that’s too slow to generate enough inertia to engage the drive gear. So, as with any system, the first thing to check if trouble develops is the battery and all its connections. The open-circuit voltage test described in chapter 5 will show you if the battery is fully charged. If it isn’t, charge the battery to bring it up to snuff before proceeding with any of the following tests. Of all the electrical circuits on your boat, the starter circuit is probably the one that draws the most amperage; until the engine starts, the starter motor needs all the juice the battery can give it. After you make sure your battery is fully charged, it’s time to trace circuits. To test the integrated system found on small engines without remote control, first check for voltage at points throughout the circuit. Figure 8-6c on page 129 shows the points to check and the sequence in which you should check them. Make sure your engine ground and the ground bolt or cable (it should be the black one) are free of corrosion and tight.
