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

Picture of Fit a Japanese Regulator Rectifier unit to a 12v AC/DC Royal Enfield Bullet
The standard, seperate regulator and rectifier units on the later model Royal Enfield Bullet are not noted for their reliability. Aftermarket replacements are available but can be expensive.

This instructable will show you how to fit one of the widely available, more reliable and less expensive integrated regulator rectifier units off a modern Japanese motorcycle in place of the standard unit.
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Step 1: Can I do this to my bike?

Picture of Can I do this to my bike?
This guide only covers Indian made 350cc and 500cc Royal Enfield Bullets fitted with the 12 volt AC/DC charging system. Given it's long production run, there are a large number of variants of these models. It is not suitable for all of them.

A few checks will tell you if this modification is suitable for your bike. You need to be able to answer YES to the following questions:

Do you have a 12 Volt battery? This modification is NOT suitable for 6 Volt systems.

Does the engine need to be running to turn the main headlight on? If you can turn the main headlight on when the engine is off, you have a different charging system and should proceed no further.

Are there four wires leading from the alternator? Follow the bundle of wires emerging from the top of the primary chaincase (see red arrow on picture). It should contain a total of four wires. Any more or less and you should stop here.
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.

emcelhannon3 years ago
Sweet ride! I love my bullet.
Thanks so much for this help, I need to do something similar with my outboard boat motor. I have an old Yamaha bike rectifier I want to put on a Mariner 4hp outboard.