At last, a simple way to end to that nagging question, "am I pulling too much power through that circuit on my bike?"
If you've ever added an accessory you've wondered that right? Especially if it was a high draw item like a pair of spotlights, a super loud horn etc. Here's a product that will let you know instantly without the inconvenience of pushing probes into fuse holders and while protecting your circuit at the same time which is not the case if you're using a standard digital multimeter.
Fuse Buddy is made by Electronic Specialties. There are two models, the 302m and 304b. The 302M is shown at the top of the photo (right) and is designed for mini blade fuses as used on most newer cars. The 304B is designed for use with the more common blade type fuses used on most newer motorcycles.
I have the 302M because it can actually be used for either type fuse box while the larger 304b can only be used with the larger fuse holder.
The device is super simple to use. Just remove the fuse to the circuit you want to test and plug that fuse into the Fuse Buddy probe (now your circuit is protected). A simpler way is to put a spare 10 amp fuse in the probe and not worry about using the bike fuse. If you choose the 302M you might have to go shopping for that mini blade fuse to leave in the probe.
Once plugged into your bike's fuse box press the button to turn the Fuse Buddy on and watch the digital readout. If your key is off and all accessories are off you should see nothing but 0.00. BUT if there is a parasitic drain on your system and something is pulling power without your knowledge (other than the dead battery you keep discovering) it will show up. Of course to check your entire bike for parasitic drain you'll have to remove each fuse and plug the Fuse Buddy into that circuit.
When you want to check power use in a circuit just turn on the key and start watching the meter. Vulcan owners take special note, if you have connected something to the headlight circuit you'll have to punch the starter button to turn your headlight on. Standard rule of thumb with electrical circuits of this sort is to allow a 20% headroom number for the fuse. So, if your circuit is fused at 10 amps, you shouldn't try using more than 8 amps for a long and healthy fuse life.
Electronic Specialties offers another model for those who already have a digital multimeter. The 301M and 303B are similar to the units shown above except you just connect the probe directly to your DMM. The test range will be as good (or as bad) as your DMM but most will test up to 20 amps which is far more than you'll be pulling through a motorcycle circuit.
Here are the power drain numbers for my '01 Nomad. You should be able to get some idea what kind of power your accessories and bikes systems are using based on these numbers:
Finally for those who always wanted to know. A relay (runs spotlights) pulls a whole .1 amp which is why you can connect them to virtually any circuit on the bike without worry.