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My motorcycle manual indicates that when the ignition switch is in the ON position, continuity should exist between the red and brown wires (which it does) and also between the black and black/white wire. Both pairs should show infinite resistance in the OFF position. The red and brown wires are working perfectly.

Strangely, however, the black and black/white wire only show continuity when the ignition switch is in the OFF position, and infinite resistance when the switch is ON, which is the reverse of what the manual indicates. Why is this happening?

YBR125 wiring diagram

Bike is a YBR125 custom.

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    \$\begingroup\$ Does thr bike work properly? We need a schematic. \$\endgroup\$ – StainlessSteelRat Apr 14 at 13:51
  • \$\begingroup\$ SJR - Are you doing those continuity measurements (I presume using a DMM) with the switch still connected to the bike's wiring? \$\endgroup\$ – SamGibson Apr 14 at 13:59
  • \$\begingroup\$ SamGibson - yes I'm using a DMM and with the switch connected. \$\endgroup\$ – SJR Apr 14 at 14:01
  • \$\begingroup\$ Are you doing these measurements with the battery connected? \$\endgroup\$ – brhans Apr 14 at 14:01
  • \$\begingroup\$ StainlessSteelRat - Can I upload a picture of the wiring diagram on here? \$\endgroup\$ – SJR Apr 14 at 14:07
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You cannot make correct continuity / resistance measurements with the DMM terminals / test leads connected to anything else that can provide voltage (and therefore current) - for example, the motorbike's battery. Doing so will interfere with the DMM readings, as the DMM uses an internal source (often a small constant current) to be able to measure resistance.

Therefore you must disconnect the switch before making continuity readings. Or, if you understand the motorbike's wiring well-enough, you might be able to make voltage readings with the switch "in situ" and determine continuity from those, using your knowledge of the wiring.

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  • \$\begingroup\$ The manual instructions say to test the switch with only the negative lead disconnected from the battery. I have just tried disconnecting the battery completely to do a test and the result was the same. I've just uploaded the schematic if that can help? \$\endgroup\$ – SJR Apr 14 at 14:30
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    \$\begingroup\$ @SJR - Hi, (a) Why are you doing this testing - do you suspect a fault in the switch? (b) Swap the two DMM leads and re-test. Same result? (c) Even with the battery disconnected (which is definitely needed, as I explained above) other connected components can also affect the result, since you are not testing the continuity only of the switch, but also components still connected to the switch. For example the black/white wire is shown going to the ECU. We don't know how that "black box" will affect your testing. So why not make things simpler - disconnect the switch completely & re-test. \$\endgroup\$ – SamGibson Apr 14 at 15:55

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