I need a wiring diagram for a...
Accurate wiring diagrams for the CT90 are fairly hard to find. When they're reprinted in service manuals, they tend to be unreadable and hard to decode.
However, they do exist. The CT90 Mailing List Page (see the Links at left) has at least one CT-110 diagram that someone uploaded to it. It is applicable to almost all CT-110s and most later CT-90s. For the very early bikes, the wiring color codes are quite different than the later ones.
A better approach
Realistically, there isn't much to the CT90 electrical system. Almost every wire in the system eventually ends up in the headlight bucket. Start there, but be careful not to pull stuff out and forget where it went. Get yourself a small multimeter (they have a little one at Radio Shack for about $15 that works fine) and get used to using it.
Minimalism
Basically, to run the bike, the only thing you absolutely must have is power to the coil and power to the points. Figure out a way to do that, and the bike should start and run. The purpose of the ignition switch, and its friend, the kill switch if your bike has one, is to get current to the coil and to the points.
Charging
The alternator has a single output wire that goes to the rectifier, which is behind the battery and accessed from the left side of the bike. The bike cannot run without the battery, though for short periods you can jumper from one battery lead to the other if you have no battery (do not short the battery if you
do
have one!). The rectifier then has a lead that feeds the battery and the rest of the bike's electrics.
Lighting
The headlight on early CTs can be switched off and thus can be turned on when the engine isn't running -- a fun way to run down the battery fast. On later bikes it cannot be switched off and is set to come on only when the bike is running. The taillight should be on anytime the ignition switch is on. Shorts in the taillight or the wires leading to it are not uncommon, look for shorts there first if things aren't lighting up.
Other things
The horn is really simple but on older bikes the switch (a pushbutton) gets dirty and the horn itself may "freeze," giving you only a little click or nothing at all. Sometimes you can revive the horn, most times you can't.
The neutral light switch is in the left side of the transmission case. The lead coming up out of the gearbox near your left ankle is the lead for the neutral light -- it's the ground for the light, not the power.
If your bike came with turn signals, it also came with a flasher relay that can sometimes stick or go bad. It's near the battery.
If you don't have a key for your bike, take the center frame cover off and jumper those leads directly to each other (the long ones, not the ones that go into the switch). The bike is then powered.
If your bike isn't charging, it's usually the rectifier. If you have a multimeter that registers AC, you can check to make sure it's putting out AC by measuring on the input lead to the rectifier. If you see current there but none at the output leads, the rectifier is bad and needs to be replaced.
The brake light switches sometimes go bad for no apparent reason. Unfortunately they're almost impossible to repair.
Last updated:
05/12/2002