The Honda CT90 "Trail 90" has a 6V single-phase permanent magnet charging system, like many Hondas of its era. These systems are often unreliable, with rectifiers prone to failure, making battery charging inconsistent. Upgrading to a modern combination voltage regulator and rectifier is a simple but effective way to improve charging system reliability and performance.

Compatibility

Our modern regulator / rectifier will work with all of the 6v single phase permanent magnetic charging systems of this era such as: S90, C90, CL90, CB100, CL100, CB125, CL125, etc. 

Preparing for the Installation

While its not strictly necessary to remove all of these components, we recommend removing this short list of parts from your CT90 for easier access to the rectifier location.

1. Brush guard/skid plate
2. Muffler
3. Air filter
4. Remove the gas tank bolts and tie up gas tank out of the way
5. Side cover
6. Disconnect and remove battery
7. Battery tray front bracket

A note on the OEM Rectifier

The OEM rectifier's job is to take the 6v AC current coming from the stator and turn it into 6v DC. Honda does not include a regulator or regulating function in their original design of the charging system. This leaves the motorcycle in a state of constantly charging regardless of what the battery is doing while the motorcycle is running, risking overcharging and damaging the battery.

Our modern regulator/rectifier updates the rectifier to a modern solid state rectifier while also adding a regulator function to monitor and prevent over charging to modern battery technology like GEL, SLA, and AGM batteries. 

*This regulator and rectifier should not be used with a lithium-ion battery

Installing the CMC Regulator / Rectifier

1. If you have not already, purchase our CT90 / Trail 90 6v regulator / rectifier right here.
2. Remove the stock rectifier inside the frame of the trail 90.
   • Honda used several versions of the rectifier throughout the different models of the CT90 from an earlier red fin rectifier to the later aluminum body style you see in our video. 
3. Using the included 6mm bolt, bolt the regulator / rectifier down inside the frame cavity. We prefer to bolt the reg/rec through the front most hole in the cavity with the wires running forward towards the carburetor.
4. Connect the white plastic harness connectors.
   • There were several different plug ends Honda used on the rectifiers over the years and it is not a given that your version of the white plastic harness connector will plug right in and match our regulator / rectifier. If you need to install a new white harness connector on the regulator / rectifier or main harness, we include a matching connector in the box. Be sure to locate the wires in the white harness connector so that the same colors connect on each side of the plug. 
5. The black wire needs to be connected to the key-on power circuit of the Trail 90. For the CT90 / Trail 90, this is the black wire circuit. Use the included posi-tap to tap the regulator / rectifier's black wire into a black 6v positive wire on the CT90 as we do in the video. 

With that now connected, the regulator/rectifier is now completely installed on the motorcycle. If you need to replace a coil, condenser, the gas tank fuel lines, or clean out the gas tank now is an opportune time as all are readily accessible. Refer to our repair articles below on how to do these jobs.

How To Clean Out Your Vintage Motorcycle Gas Tank

Replace the Ignition Coil and Condenser on the CT90 / Trail 90 - coming soon

Replace the Gas Tank Fuel Lines on the CT90 / Trail 90 - coming soon

Reassemble the motorcycle and you are ready for a ride!