Electrical Troubleshooting 101 ... How to get started

GETTING STARTED LEARNING THE WIRING ON YOUR BIKE

Here's a real life example of a problem I had on my XJ and how I used the information in the manuals to figure out what was wrong. Electrical troubleshooting is often considered a "black art" but is really a skill everyone here should acquire just like tuning or other maintenance. With a bit of practice and some basic tools you'll be able to figure out most problems yourself.

This won't solve every problem, but if you follow this method it will give you some pointers on where the problem might be hiding and will help you post meaningful questions that will lead to a quick solution. The knowledge and insight you gain will give you that great feeling of satisfaction you get from being able to figure out and repair your bike yourself.

The Problem

After getting my newly acquired parts bike home I wanted to do a compression check to see how the engine was (I know I should have done that before buying it, but I didn't buy it for the engine, just the frame). When I hooked up a fully charged battery, turned on the key (I got lights up) and hit the starter, nothing happened ... no click no whirr, nothing.

So Where To Start ???

With any type of electrical issue you need to have an accurate circuit diagram. Let's face it, you wouldn't tear into the engine without reading the manual ... well maybe some of us would but seriously, it's not the best way to go about it. Studying those weird confusing diagrams in the back of the manual might just be worth the effort. The best ones to use are the ones in the factory manuals. Make sure you have the correct supplements as well, if necessary.

A quick look at the circuit diagram revealed the START button, that's a good place to start, wonder what's connected to it? Right next to the start button is the start relay. That should at least click in and out if the circuit energising it is working. So the first conclusion is that either the relay is duffed or it's not getting power. Assume for a bit that the relay is ok, let's check the power to it, ok? If it still doesn't work perhaps we can start suspecting the relay.

A Practical Approach

Those diagrams are pretty tough to follow, all in black and white, with all the systems on the bike thrown in together ... so how can we make them easier to understand?

The first thing I did was print out the CIRCUIT diagram, and take to it with highlighter pens. I used two colours, one for the negative ground circuits (yellow) and one for the positive 12 volt power circuits (pink). I then traced the circuits following the shortest paths possible to get the starter relay to engage. If you look at the pics below you can see the colour coding for each part of the circuits on the two diagrams.

This helped enormously in figuring out how the circuit worked. For example I could see straight off that the START button wasn't switching power but actually earthing out the relay. This has major implications for how you go about checking that part of the circuit.

Once I could see how the circuit worked I then took to the WIRING diagram the same way to find how it was actually wired up on the bike.

Gee it's a Complicated Jigger this bike ...

Looking at the marked up WIRING diagram shows the circuit includes ...

One battery
Two fuses
Five switches
Three separate earth paths via the frame
Six multi terminal connectors, and
The ignition cutout relay, plus
About twenty five individual wires, plus
About fifty crimped connector joints, any one of which could be stopping it from working.

The two colour diagram shows up something interesting, only about half the circuit is switching power, the other half is "switching" earths, like the starter button, so there's little point checking the terminals on the starter button for 12 volts if all it is doing is connecting to earth.

Remember that a circuit will drop from 12 volts to zero across anything that puts a big load on it, and in any circuit there will usually only be one of these. It will be a bulb, or a relay coil, or some other device that is connected to the battery via wires and a switch (or several as was the case in my starter circuit).

If something isn't working, then the circuit is broken somewhere, and the best way to find that break is to start at the POSITIVE terminal of the battery and work your way around the ENTIRE circuit, one leg at a time, with a meter connected to the NEGATIVE terminal of the battery, until you find a terminal that has no power, or 0 volts where there should be 12 volts.

It might be a fuse, a broken wire, a corroded terminal, etc. but the first thing to do is find WHERE it is, then work out WHAT it is. Jiggling and cleaning connectors and fuses often helps, as does looking for damaged wiring, melted plugs, rusted glass fuses, etc. Just keep probing with the meter in a step by step manner until you find something that doesn't give you the power your circuit needs. A test light will come in handy for these kinds of tests.

What about the ground circuits?

The ground circuits (yellow in my diagrams below) require a different approach. Here you are trying to see if there is a continuous path between the negative terminal on the battery (the original ground or earthing point) and the negative side of the load. In my case this was the negative side of the start relay. The easiest way to find this kind of fault is to use a continuity tester or ohm meter.

By disconnecting the starter relay I was able to check for continuity between the frame and the negative side of the coil, and when this circuit showed up as being open I measured the resistance and saw it was very high (> 1M ohm) when it should have been just a couple of ohms for a healthy circuit. A careful inspection of the crimping on the terminals at the relay showed one was corroded and had overheated, partially melting the connector. Replacing the connector would have been the answer but this was a parts bike so I just jumpered it with another piece of wire to get it going.

Conclusions

None of this would have been possible without ...

a) The factory CIRCUIT diagram,
b) The factory WIRING diagram,
c) A methodical approach, testing first the power circuit, then the ground circuit, and of course
d) A test meter

But it all starts with understanding the circuit, then the wiring. If there's a specific problem you are having try this method and see how your understanding of your bike's wiring becomes magically clearer.

 

nice writeup but 2 things, some diagrams have mistakes and your really better off with a test light, a digital meter can show a good connection even though the connection can't carry enough current to do it's job, especially relay contacts and grounds

 

I'd semi-disagree on the test light idea. The key point is that tests with the meter where bad connections are suspected need to be done "under load", with the headlight on, starter engaged, or whatever it is that's not working turned on. A test light is a much higher load than a 12 MegOhm multimeter, but it's still a much lighter load than most of the equipment on the bike.

 

great write-up!

and good follow-up too.

 

Thanks for the input guys, good points both.

Regarding diagram errors, I have found two interesting discrepancies on my bike, only small but enough to throw you, I guess there's no easy answer to that one other than to deal with it on the fly. One of mine was a different wire colour on the tacho and the other was a connector that had nothing connected to it. When I pull the loom apart I'll be interested to see where it goes, but I'm thinking it's some sort of instrument accessory offered in other markets.

You'd have to be a bit unlucky to have the only error on your bike's diagram right in the circuit that's gone bad but that's what's going to happen for sure, right? We could suggest a sticky thread where anyone who finds errors in the manuals (like torque settings or wiring diagrams) can post details to there as a warning for newcomers.

Regarding the test light vs meter, I'd agree with you both, I find they have different uses for different kinds of tests. If I want to just get something to "work" a test light is a quick and easy visual check to find a break in a power circuit. Once working and under normal load that's when I do voltage drop checks to find points of high resistance (eg if a lamp is dim or a device is intermittent). Also a digital meter is really the only way to check for higher than normal resistance in an earth path or a dodgy switch (like the start button that grounds the relay coil).

 

Completely revised original post

 

This is a good description of how to go about electrical issue. I had to do this exact thing with my horn, worked fine, then 5 mins later didn't work without touching the bike.

Turned out it was a rusty connector under the gas tank. My trusty ohm meter found that one by tracing back the wires from the horn in the above fashion.

Good advise for those of us who are afraid of electrics on bikes!

 

I know this is a really old post, but I'm wrestling with a wiring problem (I strongly suspect) that's leading to a serious intermittent starting problem on my 82 xj650. My battery is good, I've bench tested both the starter solenoid and starter motor and both work 10 times out of 10, I've cleaned the starter button and switch, but nothing is making a difference. The neutral and oil lights come on every time but when I hit the button 20 straight times I get nothing (except the oil light which glows dim 2 seconds and then brightens and stays bright) and a faint click sound, no effort from the starter. Then I'll walk away for a few days, come back (without charging the battery in the interim), hold the start button and after a second's delay the starter will crank away. Can't find any pattern. Spent a few days now chasing wires with an ohm meter, not finding any smoking guns, but the wires are awfully old.

Where I'm going with this is that I love the work you did with those diagrams iandmac, but I can't read them. Is there any way you can post them as larger files? I know its been a few years, dunno if they're still handy or if you're even still monitoring this forum, but I'd love something new to work with to break this discouragement. Thanks a lot!

 

Might be the ground strap-just an idea to throw out here. good luck

 

when your starter button is down but not doing anything, keep it down and cross the two big terminals on the solenoid with a screwdriver.
the solenoid going click is only half the test

 

Nice write up pollack......

 

Faced with an Intermittent Starter and "Good" components that "Test" OK repeatedly,....

I Pull the Starter.
Eyeball the Brushes.
Douche the Electrical end.

Squirt the Electrical-end CLEAN.
Rid the Commutator, Brushes and Cap ... free from Brush Dust.

:::Open a Bottle of Isopropyl Alcohol. Leave the Seal. Prick the seal with a Paper Clip and shoot it right out of the Bottle. :::

That's the Quick-Fix;

Installing New Brushes
Overhauling the Starter
Cleaning and Grease the Planet-end.
A valuable weekend project.

But, ... when you Press the Start Button and the thing has an intermittent mind of his own, ...
The Commutator is Dusted
Or, ... you need new Brushes.