Fit a Japanese Regulator Rectifier unit to a 12v AC/DC Royal Enfield Bullet


Step 6: Testing

Picture of Testing
You'll need a multimeter for this stage.

Set it to volts DC and connect the probes to the live (yellow on red) and earth (black) wires. You should get a reading of battery voltage (around 12.5 volts or so).

Start the engine. The voltage should stay around the battery voltage of around 12.5 volts at idle. Turning on the sidelights or the brake light should make it drop to around 11 volts. Increasing the revs should make the voltage increase to over 13 volts but not more than 15 volts.

The ammeter on the dash should be sitting in the green at idle and should go slightly more positive when the revs are increased.

If you see over 15 volts, Shut it down immediately. That means it's not regulating the voltage and could burn something out. Check your connections, especially the earth. If it's still doing it, chances are the regulator rectifier unit is faulty.

If you fail to see 13 to 14 volts when the engine is revved or the ammeter stays at zero or in the negative, it is not charging. Check the alternator output by disconnecting the two violet wires and measuring volts A.C. between them. It should go up to around 30 volts when the engine is revved. If it fails to do so, your problem is elsewhere. If it does, double check your connections then suspect a faulty regulator rectifier.

Here's a video of me testing my one:

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tlebsack2 years ago
Thanks for your help. I'm pulling and replacing regulator/rectifier #4 on my 1996 Suzuki LS650 Savage. They tell me that the summer heat burns them up. Do I need to position it on the bike to catch some cooling wind?
stinkwheel (author)  tlebsack2 years ago
Yes they do need cooling but that's still quite a few to be going through. Also worth making sure they are attached to a big metal part for added heat sinking.

"Back in the day" when people used a simple zennor diode to regulate their charging system, it was common to bolt it to the back of an aluminium numberplate for this exact reason. Having it out in the breeze and attached to something metal or a big metal bracket is certainly not a bad idea.

They did seem to be particularly bad for reg/rec failures in that late 90's era. The guts of them were pretty much all made by the same company despite differing outward appearances.

May be worth trying a mosfet type reg/rec off a different model? Others have gone into more detail for fitting these as applies to Japanese bikes elsewhere on the web.