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

Part

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

This Part Fits the Following Honda Models

• CT90 K0-K9 aka Trail 90

Why You Need This

The Honda CT90 aka Trail 90 motorcycles use a 6 volt (6V) charging system; equipped with only a failure-prone rectifier, the bikes' lackluster charging system needs as much help as it can get to keep the battery topped off. After five or so decades of service, these old electrical parts are likely functioning at a fraction of their original efficiency. One of the best and easiest upgrades you can make to your bike's electrics is installing a new combination voltage regulator / rectifier. Common Motor offers these new 6 volt regulator / rectifiers for the Honda CT90 to get your bike running (and charging) better than new.

Our 6 volt regulator / rectifier comes with a male, four-pin, plastic connector installed. A four-pin female connector with terminals is included with the unit, as well as a posi-tap connector to easily splice the black voltage regulator feedback wire into the 6V+ side of your Trail 90's wiring harness.

NOTE: There were two types of rectifiers used on the CT90 throughout its production run—early (orange finned) and late (small cast aluminum finned) style. Our 6 volt regulator / rectifier works as a replacement for either style, regardless of what the bike came equipped with.

Installation Tips

1. This unit replaces the rectifier and can be mounted where the original rectifier was mounted in the frame box. The single M6 bolt included is all that is needed to install the unit to the frame box. We prefer to use the forward-most mounting hole where the old rectifier bracket mounted through the frame. Face the wires of the new reg / rec toward the front of the bike which will have the mounting holes running vertical; use the lower hole with the bolt to mount and reuse the nut from the old rectifier.
2. Throughout the CT90 production run, Honda used both male and female connectors on the regulators and rectifiers. Very early bikes even used simple individual bullet connectors as opposed to the plastic connectors. Depending on what bike you have, you may need to alter the regulator / rectifier connector by crimping on different terminals and using different connectors. If you change out the connectors, make sure the wire colors on the regulator / rectifier match the wire colors on the connectors coming from the bike's harness—red to red, yellow to yellow, etc. Very early models did not have a green ground wire on the original rectifier.
3. The black wire of the regulator / rectifier is for voltage feedback. It must be connected to any black 6V+ wire found in the wiring harness; the black wire for the rear brake light switch is a good spot to tap into. There are two different ends on the Posi-Tap, the pointed end which pierces the wire to be tapped and the clamping end that connects to the new wire. It is easiest to install the Posi-Tap on the wire to be tapped first. Cradle the wire in the groove of the threaded cap holder (the larger cap) and screw the body of the Posi-tap in place where it is finger tight. Now install the wire of the new item to the body of the tap. Strip about 1/4" (6 mm) of insulation off each end of the wire, insert the threaded caps over the ends of the wire and slightly fan out the loose strands of wire. Do not twist the ends of the wire prior to installing them in the threaded cap. Install the cap and wire into the body of the lock and begin to thread the cap in place, while keeping pressure on the wire while tightening the cap to the body. Once snug, give the wire a gentle tug to see if it has locked properly, it should not move or pull out. If it does try again, you may need to strip just a hair more of insulation off the wire.