6 Volt Rectifier & Voltage Regulator | Honda CT90 / Trail 90

Part

Modern 6-volt (6V) combination voltage regulator/rectifier for vintage Honda CT90 "Trail 90" motorcycles.

This Part Fits the Following Honda Models

• CT90 K0-K9 (Trail 90)

Why You Need This

The Honda CT90 "Trail 90" uses a 6-volt (6V) charging system, originally equipped with a failure-prone rectifier. Over decades of use, these electrical components degrade, making it difficult to keep the battery properly charged. Upgrading to a new combination voltage regulator/rectifier is one of the best and easiest improvements you can make to your bike's electrical system.

Common Motor offers this modern 6V regulator/rectifier to get your bike running—and charging—better than new.

Our 6V regulator/rectifier comes with a male four-pin plastic connector installed. A matching four-pin female connector with terminals is included, along with a Posi-Tap connector for easy splicing into the 6V+ side of your Trail 90's wiring harness.

NOTE: The CT90 used two types of rectifiers throughout its production—an early (orange-finned) version and a later (small cast-aluminum finned) version. Our 6V regulator/rectifier replaces either style, regardless of what was originally installed.

Installation Tips

1. This unit replaces the rectifier and mounts where the original rectifier was located in the frame box. The included M6 bolt is all that is needed for installation. We recommend using the forward-most mounting hole where the old rectifier bracket attached to the frame. Face the wires of the new regulator/rectifier toward the front of the bike, aligning the mounting holes vertically. Use the lower hole for the bolt and reuse the nut from the old rectifier.
2. Throughout the CT90 production run, Honda used both male and female connectors on regulators and rectifiers. Early models even used individual bullet connectors instead of plastic connectors. Depending on your bike, you may need to modify the regulator/rectifier connector by crimping on different terminals or using alternative connectors. If you change connectors, ensure that the wire colors on the regulator/rectifier match those on the bike’s harness—red to red, yellow to yellow, etc. Some early models did not have a green ground wire on the original rectifier.
3. The black wire on the regulator/rectifier is for voltage feedback and must be connected to any black 6V+ wire in the wiring harness. A convenient connection point is the black wire for the rear brake light switch. The included Posi-Tap connector makes installation easier:
• The pointed end of the Posi-Tap pierces the wire to be tapped, while the clamping end connects to the new wire.
• First, install the Posi-Tap on the wire you are tapping into. Place the wire in the groove of the larger threaded cap and screw the Posi-Tap body onto it until finger tight.
• Next, install the new wire into the Posi-Tap. Strip about 1/4" (6 mm) of insulation from the end, insert the threaded cap over it, and slightly fan out the wire strands. Do not twist the wire.
• Insert the cap and wire into the Posi-Tap body and tighten the cap. Apply slight pressure on the wire while tightening to ensure a secure connection.
• Once snug, give the wire a gentle tug—it should not move. If it does, strip a little more insulation and try again.