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The Ultimate Relay, Switch, Sensor, and Diodes Guide
SENSORS, SWITCHES, DIODES, AND RELAYS:
One of the most frustrating problems you can run into is a bike that refuses to crank over, or will crank over but won't ever fire. Assuming it's not an engine (fuel or mechanical condition) issue, then it may be caused by your electrical system; more specifically, by the rather unique system of inter-related devices that Yamaha collectively refers to as their "safety switch system". Consisting of assorted switches, relays and their wiring, you may have to do some heavy-duty electrical sleuthing in order to determine where the problem resides.
Curiously, Yamaha used the same general style of "cube" relays in a variety of different positions for the safety system, and although they all look virtually identical to each other, they in fact all perform differently. But since they are all interchangeable......a headlight relay, for instance, will happily plug into the sidestand relay wiring harness connector shell....so the first troubleshooting step is to make sure that each relay is correct and in its correct position.
For instance, the sidestand relay is a normally closed relay while the others relays are normally open. The head light relay and the ignition cut off relay (also called the neutral safety relay) both contain diodes, which means that they are controlling voltage coming from two different sources. Although they are both normally open and both contain diodes, they are still vastly different in their coil resistance ratings and are thus not interchangeable.
Since an incorrectly positioned relay will typically not work, or will work "incorrectly" when placed at the wrong position in the harness, determining whether relays are properly positioned, and of the proper "type", can save you some more painful types of troubleshooting!
If that doesn't do it, you have to start checking all of the other components......the actual switches or sensors, the diode block, etc.
The actual electrical testing of each relay differs by relay, and sometimes by model bike, and for that type of information, we will refer you to your factory or aftermarket service manual for further guidance. Make sure you have a volt-ohmmeter and a 12V power source at your disposal to check these relays.
NOTE: many of the factory and aftermarket service manuals and the factory parts diagram sometimes mis-label a relay's function----for instance, calling a sidestand relay the headlight relay----or, mis-placing the relay in their diagrams----for example, showing the starter cut-off relay mounted in position "A" and the sidestand relay in positions "B", when in reality their real positions are exactly opposite!
Also, please note that the factory and aftermarket manuals are not always very clear as to where a particular device is physically located on a specific model---in some cases, text such as "this relay is located "somewhere" on the bike"---would actually be more helpful than their generic shadow-bike drawings and "pointing-to-somewhere" arrows that passes for a location guide.
And finally, to throw a little extra salt into those pesky electrical wounds, the factory and aftermarket manuals are sometimes not quite clear or correct in illustrating the relay testing procedures needed.......in particular, the Haynes manual is somewhat of a mess, as diagrams are mis-placed or hard-to-follow while they try to cram multiple testing procedures for a similar relay onto a single page or pages.
Luckily, relays are hardy little devices, and rarely fail completely; more than likely, they are either mis-placed, or dirty (rusty) inside, and a gentle and graceful removal of the outer can will reveal their little electrical guts, which can them be cleaned with electrical contact cleaner, etc., and thus lovingly restored to their functional beauty.
TESTING SENSORS, SWITCHES, AND RELAYS:
NOTE: never assume that you have a good power supply (12V positive) at the sensor, switch, or relay that you are troubleshooting; always check to make sure that you have power to the component that you are checking:
http://www.jetav8r.com/Vision/IgnitionFAQ.html#aa3p25
Likewise, don't assume that you have a good ground, always check (or jumper to ground) to make sure. Many component "problems" are actually due to a lack of power supply or the lack of a proper ground path!
You should be familiar with the use of a multimeter; if not, here are some great primers:
https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/all
and
Brake fluid level sensor:
* held upright (as installed in the master cylinder): 0 ohms
* held upside down: infinity
Brake or clutch hand lever position switch:
* continuity test: circuit should be complete when switch "plunger" is relaxed (plunger extended out, hand lever pulled to handlebars) and circuit should be incomplete when the plunger is pushed in (hand lever away from handlebars).
Brake foot pedal (rear brake) position switch:
* continuity test: circuit should be complete when switch "plunger" is extended (out, brake foot pedal activated) and circuit should be incomplete when the plunger is relaxed (retracted in, brake foot pedal not in use).
Oil level sender (in bottom of oil pan):
* held upright (as installed in the engine): infinite ohms
* held upside down: 0 ohms
Neutral switch (in bottom of engine case):
* continuity test: circuit should be complete when switch "plunger" is "closed" (transmission in neutral) and circuit should be incomplete when the plunger is open (plunger extended). Note that the switch completes the ground circuit from the neutral indicator light to the internal shifter drum, and not to the neutral switch "housing" (on 650 thru 1100 models).
Sidestand (kickstand) switch:
* continuity test: circuit should be complete (0 ohms) when switch "plunger" is extended and circuit should be incomplete (infinite ohms) when the plunger is pushed in.
Sidestand (kickstand) relay:
- due to many variations in design and the need for visual reference, you should check your service manual for the proper testing procedures. There are at least two checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check.
Diodes:
- due to many variations in design and the need for visual reference, you should check your service manual for the proper testing procedures. Basically, a diode allows current to flow through a circuit in one direction only; therefore, when tested with a continuity meter, should show continuity when checked with the probes placed in one orientation, and then when the orientation of the probe leads are reversed, no continuity (no circuit).
Starting/Ignition Cut-Off/Neutral Safety relay:
- due to variations in design and the need for visual reference, you should check your service manual for the proper testing procedures. There are at least three checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check, and a diode function test.
Starter motor solenoid/relay:
- due to the need for visual reference, you should check your service manual for the proper testing procedures. If the use of a screwdriver blade across the two large threaded stud terminals results in the starter motor operating, then the "solenoid" portion of the unit is operating properly, and it is the "relay" portion of the device that may be defective.
Emergency stop switch:
* continuity test: circuit should be complete (0 ohms) when switch is positioned at a 60-degree rotation from vertical (in either direction) and circuit should be incomplete (infinite ohms) when the switch is positioned vertically.
Emergency stop switch relay:
- due to the need for visual reference, you should check your service manual for the proper testing procedures. There are at least two checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check.
Fuel pump relay:
- due to the need for visual reference, you should check your service manual for the proper testing procedures. There are at least two checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check.
Manifold pressure sensor:
- due to the need for visual reference, you should check your service manual for the proper testing procedures.
Headlight relay:
- due to many variations in design and the need for visual reference, you should check your service manual for the proper testing procedures. There are at least three checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check, and a diode function test.
For an on-bike test, you can:
- disconnect the White with blue tracer stripe wire at the headlight relay.
- turn on the ignition - the headlight should be off.
- momentarily jumper 12V to the pin on the relay where the white/blue wire was connected, and the headlight should come on and stay on.
Turn signal flasher/relay:
- due to the need for multiple tests, you should check your service manual for the proper testing procedures.
Flasher self-canceller:
- due to the need for multiple tests, you should check your service manual for the proper testing procedures.
BY-PASSING SWITCHES AND RELAYS:
How to bypass various relays: first of all, our advice is DON'T. The relays and switches are there for a reason....your safety, to prevent "mistakes" from turning into "disasters".......so our recommendation is to just leave the system as it is, and replace any components that fail. However, for failure testing purposes, it may be necessary to temporarily "by-pass" certain components, thus eliminating their functionality from the circuit, to see if they are the source of whatever problem is occurring.
Sidestand (kickstand) switch:
- twist the two (or three, depending on the model) wires together and ground them. Grounding the wires is the only way to complete the circuit that activates the sidestand switch relay.
Sidestand (kickstand) relay:
- unplug the safety relay which disables the whole bloody mess but DO NOT leave it that way, fix it right!
Starting/Ignition Cut-Off/Neutral Safety relay:
- unplug the safety relay which disables the whole bloody mess but DO NOT leave it that way, fix it right!
Clutch hand lever position switch:
- jumper the wires (on the main harness) to each other, the circuit will think the hand lever is pulled in.
Neutral switch (in bottom of engine case):
- jumper the lead wire to a known good ground; if the neutral light comes on (assuming the bulb is good!), then the wire circuit is good. If the neutral light will still not light up when the transmission is in neutral, you can try jiggling the switch slightly (tap on it with a screwdriver blade, etc.....it's hard to reach) or tightening the switch slightly. Otherwise, the switch is either bad internally, or the brass plunger has worn down to the point where it cannot make contact with the shifter drum plunger (550 models) or the drum itself (650 thru 1100 models) and should be replaced.
Headlight relay:
- bypass the relay by connecting the Blue wire with the black tracer stripe directly to the Red wire with the yellow tracer stripe.
http://www.xjbikes.com/forums/threads/electrical-gremlins-headlight-relay.63436/#post-460696
Starter motor solenoid/relay:
- use a screwdriver blade to cross the two large threaded stud terminals. If this procedure results in the starter motor operating, then the "solenoid" portion of the unit is operating properly, and it is the "relay" portion of the device that may be defective.
Fuel pump relay:
- unknown
Emergency stop switch relay:
- unknown
XJ700 water-cooled models thermo unit and thermoswitch:
- the water-cooled XJ700 and XJ750-X engines use a an electrical thermo unit and thermoswitch to sense and relay information to the temp gauge (how hot is my coolant?) and to the fan motor (turn me on or off). Both of these devices screw into the thermostat housing.
The procedures for the testing of the temp gauge sending unit (the "thermo unit" with the single electrical terminal) and the fan control switch (the "thermoswitch", which has 2 electrical terminals):
Thermo unit:
1) do not drop this sensor! If dropped/shocked, it should be replaced, regardless of testing to specifications or not!!
2) Testing: immerse in cool water. Attached ohmmeter leads (+ lead to terminal, - lead to body of unit) and slowly heat the water. Measure the resistance at various temps. Specified values are:
156 ohms resistance at water temp = 122F
28.4 ohms resistance at water temp = 212F
17 ohms resistance at water temp = 248F
Make sure your thermometer is accurate!
Thermoswitch:
1) do not drop this sensor! If dropped/shocked, it should be replaced, regardless of testing to specifications or not!!
2) Testing: immerse in cool oil. Attached ohmmeter leads (+ lead to one terminal, - lead to other terminal) and slowly heat the oil. Measure the resistance at various temps. Specified values are:
Heat-up tests:
infinite resistance at oil temp between 32F - 208.4F
0 ohms resistance at oil temp between 215.6 - 226.4F
Cool-down tests:
0 ohms resistance at oil temp between 226.4 - 208.4F
infinite resistance at oil temp between 208.4 - 32F
Make sure your thermometer is accurate.