Free printableElectrical and wiringTSP-EL-07
Testing a scooter stator and regulator without a spec sheet
Open, shorted, or plausible. Three states that need no reference figure and catch most real failures.
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TSP-EL-07 · version v1.0 · September 2026. Opens in your browser's PDF viewer, where you can print directly.
The problem it solves
When a machine will not charge, the stator and the regulator are the two components blamed, and both get replaced in turn because there is no reliable way to test them — or so it appears. Published resistance figures for these parts disagree between sources and between suppliers of nominally identical components, so testing against a number frequently condemns a good part.
There is a way to test these that needs no reference figure at all, and it catches most real failures. A stator winding is either continuous, shorted to the engine case, or somewhere plausible in between. Those three states are distinguishable with any meter and no specification, because open and shorted are absolutes.
The regulator is tested by behaviour rather than by measurement: does the voltage at the battery rise when the engine is revved, and does it stop rising? Two observations, no target number, and between them they separate not charging from charging from overcharging.
What this will not do is catch a winding that has partially failed but still reads plausible, or a regulator that is marginal. Those exist. But they are a small minority of failures, and the alternative — condemning parts against figures that disagree with each other — is worse than an honest partial answer.
The mistakes this sheet exists to prevent
- Testing a winding against a resistance figure found online, which frequently condemns a good stator.
- Testing with the connector still plugged in, so you are measuring the whole circuit rather than the component.
- Buying a regulator because the machine will not charge, without checking the earths first.
- Ignoring the stator's wiring where it leaves the engine case, which chafes and is far more common than a failed winding.
- Testing with a battery too flat to crank properly, which makes every reading unreliable.
Who it is for
- Anyone whose battery will not charge
- Owners who have been told the stator or regulator is at fault
- Anyone who has already replaced one of them with no improvement
What is on it
- The open / shorted / plausible method, and what it does and does not catch
- Regulator testing by behaviour rather than by number
- The chafe point that is more common than either component failing
- A record block for the readings
How to use it
- 01Check the earths and the battery first. Both make every reading below unreliable.
- 02Unplug the component before testing it, so you measure the part and not the circuit.
- 03Test each winding to every other, and every winding to the engine case.
- 04Inspect the wiring where it leaves the engine before condemning anything.
Use it with the registry
Other sheets you may want
- Battery and charging system test sheetThree voltage readings diagnose most electrical faults on these machines. Two thresholds are sourced; the rest is direction of change.
- Scooter earth and ground connection checklistA corroded earth produces the same symptoms as a dead ignition component, and costs nothing to fix. Check these before buying anything.
- GY6 wiring colour and continuity notes sheetThere is no universal wiring colour standard on these machines. This sheet records the one your machine actually uses.
Free to print, copy, and share — including in forums, clubs and workshops. If you find a mistake on this sheet, tell us and it gets corrected. Quote TSP-EL-07 and the version so we know exactly which sheet you mean. All printables.