New to forum so thank you in advance for any help. Reviving a 74 st90 and trying to figure out what prev owner had going on with the battery connections. No battery was in bike when I acquired My questions are...does the green wire from harness connect to green from battery? Does it anchor to the battery holder frame that would ground to bike? I have A loose yellow wire from rectifier. Assume this connects back up to rectifier in a empty spot? I have 2 red male plug in from harness..assume they go to 2 red from battery. I have A light blue and orange from harness...I have No rear turn signals, are these for turn signals ? I hope picture loads. Thank you
We REALLY gotta' talk about jettisoning that toxic, heavy metal, inefficient loser of a selenium rectifier. There are far better choices in a modern, solid state, silicon rectifier that will run cooler and be worth nearly an extra volt DC at the battery - from Digikey and Mouser Electronics -- part number GBPC2504-E4/51GI-ND from Digikey --- less than five bucks. But I digress.
The green wire is ground and its eye connector bolts to the frame at a clean connection with no rust. The red/white stripe wire heads to the rectifier and has no fuse inline. The red wire heads toward the fuse (15 amp) and the remainder of the bike wiring harness. The other two wires coming out of the stator head to the rectifier and their position there does not matter for polarity.
You are likely new to the 90 CC bike world and you now must learn that a good battery that can accept recharge current is the voltage regulator for these bikes. Without a healthy battery, as soon as you rev up the engine, that extra juice coming out of the stator has nowhere to go. Every operating filament in every lamp on the bike will then burn very brightly but only for maybe two seconds. And headlights get expensive on these bikes.
Thank you lukelaw1 and b52bomadier1. Yes I am new to a ST90. Since I recently retired I am getting to some of my projects...anyway, thank you Rick for advice on the rectifier as I will order one ASAP. Assume I can refit the wires with the correct female connector and plug the 4 wires in randomly. I will keep the toxic, heavy metal, inefficient loser of a selenium rectifier in case the next owner wants to go original equipment. I do have a green wire coming out of harness that needs a home, would this go to the frame as well? There is a eyelet bracket that comes off the rear of the battery bracket that looks like it should have something attached to it. Lastly, the light blue and orange empty female wires towards the taillight, are those for the turn signals? The bike has no turn signals on the rear. I know lukelaw1 attached a wiring diagram but I like confirmation before I burn up stuff from a wrong connection. Thank you!
When your new rectifier gets here, you will notice that one tab on it that is turned differently than the other three. The red/white wire goes there. Directly diagonal across from the red/white wire will be the ground wire. The two remaining tabs are for the two wires coming out of the stator that carry the alternating current as inputs to the rectifier. For these two alternating current wires, polarity into the silicon rectifier does not matter.
Use a bolt through this rectifier to attach it to the bike frame or the battery box because it does generate some heat. You can test your rectifier wiring and its performance with a multimeter set to its lowest AC volts setting. With the bike running at about half throttle, probe the battery and hope to see maybe .1 to .2 volts AC there - a tiny amount. Much more indicates a leaky diode in the rectifier an AC juice into a DC battery is never good.
ST90 bikes typically shred their rear turn signal mounts the first time the bike is laid down in even a small crash. The rear turn signal mounts are part of the tool box and good undamaged tool boxes are hard to find. Another hard to find part is a good speedometer cable.
And yes, those blue and orange wires are for the rear turn signals.
Your statement "plug the 4 wires in randomly" concerns me . . . .
Your response on where to plug in the wires on the new rectifier eliminates the random part...thanks! I will inspect the turn signal housing on the tool box to see if this will be a bigger challenge to repair. I noticed in some other threads the luggage rack is a tuff find...mine is in great shape! The speedometer shows 1700 miles...once running I can see if operative(seems highly unlikely). I noticed after some research, there is a mount coming off batter bracket that looks like the rectifier was attached to it? You mentioned to mount new rectifier to batter bracket and I assume that's where to attach. Could you tell me where the green wire from the harness goes? The previous owner soldered a male connector to the original eyelet connection(have no idea what he plugged this into, you can see in pic I posted).
Green wires should be grounds (negative battery / frame) but without knowing what previous owners have done, its impossible to be certain from here.
There was an ST90 tool box turn signal mount repair discussion around here that I can't find anymore. There was a guy in that thread that fabbed up new turn signal mounts onto a shredded tool box and did excellent metal work and even better welding.
That guy could make metallic boobs and weld them onto a female snowman. He was that good.
What are you seeing for AC and DC volts at the battery with the engine running about half throttle? Your wire connections are properly made but I would put some heat shrink tubing over the exposed connectors to prevent shorts.
This rectifier, if you bought the recommended part number, is a rock crusher compared to your old selenium rectifier. As long as you don't flip the headlight switch on and off at high RPM a lot, it'll be virtually impossible to destroy this rectifier.
Thanks for your help through this. I have a fuel issue....the bowl is not filling up. I totally tore it apart and cleaned but I may need to soak it. It hasn't been running for some time. Everything was all gummed up....I went through tank, new lines etc but I don't think my float is working properly. It did run a couple of seconds on starting fluid so that's a good sign. Good call on the shrink tubing. I will test battery once I get this sucker running. I have never been around a ST90 and I must say I am starting to like this bike. I am recommissioning my 72 CT70H that I bought new at the same time. Stay tuned....thanks again, Terry
Do you have normal fuel flow through the tank valve down the fuel line and into the carb? With the bowl removed, see if fuel flows through the major passages and if you can control the flow by hand by raising and lowering the float.
And use some rubber gloves and a fire extinguisher. Fuel is nasty stuff.