Miscellaneous Electrical Q's FAQ
compiled & edited by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.

If you're looking for information on Aftermarket lights see Aftermarket Lights FAQ
If you're looking for GS-Specific information see Electrical Misc Qs GS
If you're looking for Accessory Socket information see Accessory Socket FAQ
If you're looking for Instrument Lights that don't work, see the Dashlights FAQ
If you're looking for the Classic Sidestand Switch Bypass Procedure, see the FAQ
If you're looking for info on Spark Plugs see the FAQ
If you're looking for info on Horns see the FAQ
If you're looking for info on Heated Grips see the FAQ
If you're looking for info on an On-Board Voltmeter
If you've had a Bizarre Breakdown it might be the Ignition Switch
If you're looking for info on the Brake Light or the Brake Switch

What is the Capacity of the Charging System

Testing " Ground"
Hombre Sin Nombre, November '01

HOW do I test the Ground.? This explanation is for the Voltage Regulator but applies to all "Ground" Testing.

You can test your battery ground connections the same way - Take your (Digital Volt Meter) DVM, set it for the lowest Ohm setting, often 200ohms. Put one lead to each side of what you want to test - in this case clip one end to a good frame ground, or the battery negative terminal (especially if you want to test those connections also) and place/poke/connect the other test lead on the VR ground terminal. (You are measuring across the gap, across the joint between the VR ground terminal and the frame, right?) See what the DVM says - it should be less than 1 ohm. Actually it should be almost the same as the reading you get when you short the DVM test leads and get the resistance of the leads themselves, about .2-.4ohms or so. If you get 2-3-5 ohms, or more, it's not a good connection. I grease those connections also - the original VR frame ground spot was a nice polished surface where the connector clamped. With my VR questions, I tested across all my ground connections on the engine and frame this way.

Note that the first thing to check in ALL electrical problems is the ground to the battery. The fuse pops upon hitting the starter because the starter is drawing too much juice (i.e.., too many amps, too much current). So, check the battery ground FIRST (don't just check that it "looks" like it's connected, make sure it's tight), then check all connections to and from the starter (like the solenoid connected to the positive pole of the battery) and go back from there to the handlebar switch. I'll bet good green American money that it's a very simple problem. Shank, NYC.

What is the Black Box in the Tail Section.?
Flash #412

There SHOULD be a black box in the tail section. That is for ignition. If you look at the wires near the tail section, there SHOULD be two blue wires, one with red trace and one with black trace that are not connected to anything. These are the turn signal wires that the alarm plugs into if you have one. (But the REAL turn signal wires/connectors are in that vicinity, too.) Take a look at the wiring diagram in the FAQ. That SHOULD help figure out IF you still have an alarm or not.

Which sensor wire turns on the Fan and Which one the Temp Warning Light.?

Typical Problem:

Got on the bike this morning and as soon as I switch on the 20A fuse blows. A bit of high-tech wiggling of wires and several fuses later I have identified the problem to be with the wiring to the rear of the thermostat cover. Thank you for the wiring diagram Flash - not for the first time you have helped me in my hour of need. (I think you're missing something on the horn switch, though).

My questions are (Irish F650, 1997 - has clock not temp. guage).

There are two seperate sensors on the thermostat cover, is one for the temp. light and the other to activate the fan? Which is which? The one at the top has a single wire, the one at the rear has two wires. Why two wires if this is a thermal switch routing current to earth?


Do you have a LIST of the Bulbs used on the Classic F ?

Flash #412

All of these are for F650 Funduro and ST through Y2K, e.g.
"classic" F650's.

Light Bulbs 101 - Halogen Bulbs

by Flash #412

Tracing Problems Where the Fuse Blows all the Time - i.e. Testing for Shorts.

Shorts - General Test Sequence
by Bill #1031

Shorts - Blown Ignition Fuse Cure
by Lee#1106, CT.

Shorts - any other advice?

from Flash #412

Shorts - Blown Fuses - Feedback

DC Electrical Basics - The Charging System
by Gerry #951

In answer to the Question,
how do I measure the Power Draw of each item on the Bike, like my Lights, my Heated Vest, my Heated Grips.?

While everyone argues about nomenclature, I like to keep it simple. Consider this: Use Ohm's law and it says V (voltage) = R (resistance) x I (current)

1. Voltage is simple to measure as is resistance. Place your leads across the items being measured and have your meter on the appropriate settings for either resistance or volts.
2. In the case of a resistor or a resistive load like a lamp:


Touch the probes here (marked I) so that the meter is in parallel to the circuit being measured.


3. If your meter measures amps, it has to go in the circuit being measured. The left end is the battery and the rest is the positive lead:

+---------------------------------------------(pos. lead)

Putting your meter in series means going between the battery and the lead where (A) is your meter:

+-----------------(A)------------------------(pos. lead)

You have to break the circuit and put your meter in between. Also called being in series with the circuit, or being a part of the circuit. I haven't picked up a meter in a long time but I seem to remember that most will only handle around 5A, though that may be 10 A by now.

Measuring the amps for each item may not be necessary. Watts is simply volts x amps. In the case of a 60W headlight and a 12-volt system, you're pulling around 5 A, in theory. Our bikes run at more than 12 volts so use something a little higher and you'll probably measure 4.5 Amps. As the volts go up, the amps go down. Simple.

If you pull each major subsystem and make your measurement, you'll figure out where all that power goes. And if you're putting out more power than you're putting in, give me a call, we're going to make a fortune with that circuit.


Current “Simply Explained” 

Flash #412

When considering electrical (not electronic) parts, how do the power ratings correspond? For example, how does a switch that is rated for 5 amps and 125 VAC correspond to a 12 volt direct current system? Is actually peak power that matters? Can it even be correlated?

Current is current. But AC is "self-extinguishing" in a switch. What that means is that a switch designed to switch 125VAC (at 60Hz) only needs to be able to maintain an arc of rated current for 17 milliseconds, max, before the signal "turns itself off."

Inductive loads "fight" being turned off. L*di/dt is power, too, not just V*A. So if you happen to KNOW the inductance, in Henries, of your load, you can calculate how much current will arc through the switch in 17mS to determine if you're overreaching the capacity.

The short, real world answer is... use a switch that's AC-rated for the same DC current you plan on running. If it doesn't last as long as it could or should, so what? You'll be replacing it in a year or five. So what. It might last forever. Is it worth that much of your time wondering about a $2 part?

Next time you go to Home Debit, take a CLOSE look at "standard light-switches." There are really THREE kinds. One is "T" for standard lights (tungsten). One is (either "I" or "M", I forget) for motors aka inductive loads. And the other is "F" (I seem to recall) for fluorescent bubs. Each is constructed to manage it's specific purpose. But nobody ever pays attention to which one they get anyway.

Refer also to the Battery FAQ and the The Voltage Rectifier FAQ

What about using Circuit Breakers rather than fuses?

Q. Any reason why a circuit breaker board couldn't be used in place of a fuse panel on a 650 or other bike? Is it cost or other reason why fuses rather than circuit breakers are used? Seems circuit breakers would be a lot more convenient.

What's a Good Spray for Protecting Electrical Connections

I put in a new Flasher Bulb and it doesn't Flash?

Harl #380

The wattage of the lights you're installing is different than the stock lamps. Either match the (wattage of) stock bulbs OR as the flasher is a thermal device that works on total current flow and changes with the draw, install an electronic flasher rather than the thermal one.