My two cents:
Lots of methods can result in the same conclusion. Light bulbs can be useful but can never substitute for a meter. But a meter being used by an someone who does not understand how they work is worse (sometimes). I have a couple of different light bulb rigs but rarely use them. Rarely as in almost never. You can see gross differences in voltage drops, but you still need to use a meter anyway so I never carry them in my kit despite the simplicity of them. I even have one of those automotive style probes but hate them on boats.
Dropping the meter is a constant worry though I admit. Mine has a ammeter loop clip that I clip on to handy places when possible. It is sometimes a real pain to be able to put the meter in a place you can see it while you turn things on and off. But alligator clips often simplify things as I can just hold the meter in one hand while I move the other test point around checking things (see below).
Regarding voltage drop (see the boatdieselusa website link previously given above), this is way beyond what I have seen as readily done for several parts
of the circuit troubleshooting noted in the article. Especially when it says to control the system current
to 500A or to 100A. LOL - do any of you have a current
limiter that works up to 500A? You don't need that type of equipment
to do the test though but your test won't be good to as many decimal places. To do these tests you have to be sitting by the engine with your meter connected to the appropriate points while someone cranks the motor
. So you need two people and have to be very careful around moving equipment
and high currents And the article does not really tell a novice
how to fix the problems.
And, I routinely successfully troubleshot circuits without ever measuring voltage drop. Does it work as a method, sometimes when no other method (like measuring resistances or small currents)? Yes it does. Voltage drop is the only way to check resistance in big cables
such as the battery cables
, solenoid contacts, and battery switches but is not that much better than using a simple Ohms reading across panel switches. Rarely does a big battery cable have a "hidden" voltage drop under the insulation
. Inspect the connections, take the connection off the starter, switch, or whatever. Look at it and wiggle it. If it is loose or corroded, remove the crimp, and recrimp on clean wire. If there is any corrosion cut the wire down until it is 100%. Replace it if unsure or too short. Get a professional crimp - never, ever use jury rigged or hammer-type crimper. Use quality wire. Otherwise, clean the terminal and the crimp and put it back on to a proper torque (approx). Make sure the big wire is the first one on, etc. etc.
Ohm meters cannot generate enough current to test big cables or switches but is fine for smaller switches and wires. And an ohms meter tests for open circuits immediately without setting up for a voltage drop test or making sure you have good battery voltage to the device. Not useful for some things like solenoids though (unless they are NC - normally closed). Starter solenoids are usually NO - normally open so you can't test resistance on the contacts. You can't do that for the big starter solenoid anyway. If it comes to that, a voltage drop test can work but can be difficult to set up because the solenoid goes open after the engine starts (normally) so it is transitory and you have to be there and observe fast and have alligator clips, etc. etc. Automotive techs don't routinely do this (to my knowledge) without special equipment. They'll just routinely replace the starter/solenoid as the cheaper alternative after isolating the problem to them.
I have two 14 ga 2' lengths of wire, with small/medium alligator clips soldered to them with alligator clip covers. As noted above, they are so useful I always have them in my meter kit and use them almost 100% of the time. I use one black and one red, although that really doesn't matter electrically, it can make it easier to think through what you are doing. You put the red one on the red meter lead and the black on the black lead.
It is much easier to test circuits in many cases by freeing up your hands while you turn things on and off. You have to make sure you have a good contact by the clips to the test leads and again with whatever you connect it to by wiggling and then testing the Ohms reading between the leads themselves. If no good connection between the clip and the test lead, or the clip at the other end to the circuit, you'll get a false reading.
I use them about 90% of the time, especially trying to find a good ground. You can never assume you have a good ground for a voltage test (e.g. do you have battery voltage at a particular spot or not). Often it is the ground that is bad, not the positive.
can learn a lot about troubleshooting circuits and devices but a starter circuit is one of the most complicated on a boat (excepting electronics) there is. Not the place really to start unless you have a way to narrow the scope
of the troubleshooting and take your time and understand each part as an isolated part and master the testing for that particular part of the circuit.
You CAN successfully measure Ohms across switches and small wires without disconnecting the switch from circuits but I do not do it on live circuits. This is usually easy to do by turning the battery switch off. It is really not necessary to do that in most cases. But don't try that with the meter on amps except on very low amp circuits. I almost never try to measure amps on low load circuits. I do on starter and alternator
tests though with my clip over ammeter, or, for identifying circuits going on/off, etc. And, I have successfully troubleshot bad connections (like engine wiring cable plugs) with just the ohmmeter. It often, not always but often, can show a bad corroded connection that way. If it doesn't, it doesn't mean the connection is 100% good, but it will tell you if it is very bad. I have found most problems result with the "very bad" rather than not so bad. So I can quickly try to go through a system checkout without elaborate more sensitive tests. You may have to go back and do a more sensitive test if nothing else works.
BTW - the very simplest test is visual and tactile sensing. I.e. look for bad or loose connections. Number one check you should always, always do. Positive and negative sides. Often key switches or glow plug switches or start switches will work when is it found that the helm panel has a bad negative ground. They are often in wet locations subject to rain and splashes of salt water
, with lots of vibration. But I would start with looking at the easier things to look at first - like connections to the starter, battery, battery switches, ground wire to the engine block if I really don't know what is going on in the first place. And look at the engine to helm harness plug. They go bad (as mentioned earlier in this thread) often. Sometimes one of the specific connectors in a block gets pushed back and doesn't connect with the other side. Make sure nothing is loose and nothing green. Tug on the wires going in to each plug (gently).
Someone said above that some people have a tough time understanding and mentally imaging electrical
circuits. I would say that most don't. Some can get enough experience to overcome this and "getting" it, but some never can. To others it just comes naturally. I am sort of in between. I like to draw out diagrams or use ones provided. It helps me to visualize the circuit and make sure I have not missed something.
Nothing to be ashamed about. I don't write poetry either. But it's not dangerous or expensive if I never "get" it. Mis-wiring a boat can be destructive and sometimes dangerous, even fatal. Sometimes you just have to bring out the checkbook and have it done by a professional. Sometimes it is worse by having your dock
buddy or house electrician "help" you. Boats are NOT the same as houses.
Anyway, sorry for being so windy, but there is a lot to troubleshooting and knowing how to use the tools and methods required. Lots of amateurs successfully do this though but you need to recognize if you are one of those and act accordingly. I don't rebuild
engines because I am not trained, don't have the special tools, and wouldn't know when to use them. I think I could learn but that is an investment I don't have money
and time to do. I'm hiring someone to adjust my rigging
next week too.