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Hunting down a mystery draw on the 10 amp circuit of a 2018 urban g/s

2545 Views 52 Replies 15 Participants Last post by  BlitzSchnell
2018 urban g/s with 20k miles.

I ride daily and noticed a pattern where every 2 or 3 weeks the starter is sluggish and the battery voltage low. Bike may or may not start.

I get the following sequence on 2 batteries, the original and a replacement, both are AGM, lead-acid, load tested and solid.

I have added some electrical things like running lights, phone charger, and all are disconnected before I run the following sequence.

Morning, bike not started since previous day, fuel pump disconnected, tank up, multimeter gator clamps directly on battery terminals. Terminals clean, connections tight. Voltage reads 12.87. Insert key, turn ignition on, do not touch starter button. Voltage instantly drops to 12.4 as I hear the fuel pump cycle, I hear the exhaust flapper servo cycle, and then silence, in the headlamp the 5 watt running bulb is on, otherwise, nothing on, may be the rear brake LED running light, silence. Voltage continues to drop, 12.3. At this point the starter if fired will feel sluggish or may not turn over at all. On occasion I have seen voltage plummet to 11 and 10.3. Then I turn key to off and remove it. Voltage remains constant at say 12.4 or 12.3 and continues dropping until, at exactly 1 minute from when I turn the key to off, I hear and feel a relay in the flapper servo open, a split second later the main relay opens, and instantly, the voltage jumps a 10th of volt, to say 12.5, and keeps on rising steadily back too 12.7 or 12.8.

I pull the 4 amp fuse and the draw persists. I pull the 10 amp fuse and it stops. So seems to be on the 10amp circuit.

I remove the silencer and observe the servo move the flapper normally. Disconnect the flapper servo and turn the key to on, the draw persists. The main relay tested fine, but I replace it, and the draw persists.

I disconnect the fuel pump on the underside the of the tank, and the draw persists.

I disconnect ABS module. Draw persists.

I run the GS-911 and get no faults, all green. I have run the tests in the scanner including those on the flapper servo, fuel pump, and passed all tests.

Does anyone else find the same 1 minute shutdown sequence?

Does anyone know more about what is going on in this sequence and what might be able to cause a strong silent draw?

I have more experience with marine electric, and in those cases, when I saw similar voltage drop on the battery bank it was something like a bilge pump drawing near 10 amps or maybe a momentary drop by a refridgerator compressor firing.

I suspect this draw is maybe 6-8 amps.. it it was over 10 amps it would blow the 10 amp fuse, but that's never happened.

Thanks for reading.

Any ideas appreciated.


Today after posting I began to disconnect components one by one. Disconnect, turn on key, watch for voltage drop, turn off key, observe voltage, reconnect. After about 5 cycles of running this sequence, that is to say, disconnecting 5 components, the voltage drop goes down into the 10 volts.. then 1 minute after key off, you hear the clicks of the 2 relays, and within 1 minute the voltage is back up to 12.6 volts. But at this point, I connect the 2amp noco charger and let the battery top off before I continue testing. So far none of the components I disconnect results in any change in the voltage dip. I do not know every component I have disconnected, but I have taken a pic of each and marked the connector with a white grease pencil. I could work to identify each one, but my plan is to wait until I see the voltage drop stop, at which point I will identify.

Here are the components I am familiar with that when disconnected that have no affect on the voltage drop:

  • exhaust flapper servo
  • fuel pump
  • ABS module

Attached is the wiring diagram from my Haynes manual.


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Heat grips?

You ride Daily but how many kilometres? Engine get enough revs?. Probably battery is not able to charge properly in this situation and get weaker and weaker...
Good guess but the alternator starts charging at very low RPM’s … I don’t believe that is the issue … I’m inclined to think direct short to ground as in a worn or bare wire that’s shorting out …. 10A is a load ! ………………..Blitz
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Thx, I have not gotten into the switches yet. One by one, with the tank up, I disconnected 10 components, and cycled the key on/off watching voltage. The voltage always dropped regardless. Then I tried @IanHoots idea and got a thermal imager. Low and behold, the idle actuator lit up like a candle. I had already tested them individually, but I thought, perhaps they must both be disconnected at the same time. Nope. Same voltage drop. But very cool idea and good to see that I could not find any hot spots.

View attachment 160242

Just above my index finger you see the idle actuator, a bit blurry in the background, but that's what is showing warm in the lcd screen. For anyone who wonders, above that and going over the air intake is the black flexible conduit, the wire loom, which is carrying all must custom wiring for running lights, horn relay, and phone charger, all of which are individually slid into braided cable sleeve. All my previous electrical problems, with other bikes, have been due to wire coating being rubbed off and touching the frame, usually combined the the fact that a wire was not properly routed or secured, so this time around, I took no chances. Everything is then zip tied, or sometimes while working out the routing, I will temporarily use velcro cable ties, then once the design is set, secured with zip ties. All my work goes into the healtech tb-usb2, which is connected to the battery thru the positive bar just behind the tank, and a rock solid ground. This heal teach unit only turns on power to my peripherals once the bike is running and rpm's are above idling. Main goal being, nothing I wire up can pull power until the alternator is cranking. The other goal, is that in troubleshooting times like these, to disconnect all my work, I simply disconnect the healtech unit. And another benefit is that you dont get a stack of eye connectors piling up on your positive post.
Your logic and applied experience are real jewels for me thanx …. and the thermal gun idea was brilliant !
Great logic and creative thinking… thanks to all contributors. You’re why this forum is so … Cool ! ………. .I Learned a great deal……thanks for sharing your time…..Cheers Mates ………………….Blitz ✌🏻
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