ST80 solenoid

[IowaV8]

I had to replace one of these on my 01 bike, but my 04 was still using the original...until today! I've always had a spare so had one to use. Went to go for a ride today and when I turned on the key my voltage went from just under 8 to 0 and heard a buzzing under the seat, so suspected this was the culprit. I have a Truk Lite 7 headlight and noticed for a while then I turned on the key before starting the light would flicker, but quit that when running. After installing the new one it doesn't do that anymore so it must have been failing for a while, but showed 14 volts when running. Now I'll have to get another spare, but it's fixed! Glad I was home when it happened. I had an overly helpful neighbor come into the garage and told me I should have just taken it over to the Harley shop.....Yeah right!

[V8Bikers]

Frustrating for sure when these issues pop up all of a sudden! I have had a few things happen over the years that were in the driveway or garage. Still pissed but glad I did not need a tow.

[IowaV8]

That's what is so great about this forum and the older one that I used for so many years. With all the knowledge and advice you get from fellow riders you can usually figure out problems and remedy them due to the fact others have run into the same thing and posted about it. Our "local dealers" are often several states away, so it's a lot of do it yourself.

[hogv8]

I've heard from a reliable source that if you run a jumper wire from one large terminal to the other on the ST80 it wil work in an emergency. Never tried it but I aways carry a made up jumper wire just in case . I also carry a spare ST 80 but the jumper wire wold get you back running quicker if on the road .

[mmaupin]

I've heard from a reliable source that if you run a jumper wire from one large terminal to the other on the ST80 it wil work in an emergency. Never tried it but I aways carry a made up jumper wire just in case . I also carry a spare ST 80 but the jumper wire wold get you back running quicker if on the road .

I would make sure it is a heavy duty jumper wire / same size as the battery cable that feeds the ST80. A lot of current passes through that solenoid.

[hogv8]

I've heard from a reliable source that if you run a jumper wire from one large terminal to the other on the ST80 it wil work in an emergency. Never tried it but I aways carry a made up jumper wire just in case . I also carry a spare ST 80 but the jumper wire wold get you back running quicker if on the road .

I would make sure it is a heavy duty jumper wire / same size as the battery cable that feeds the ST80. A lot of current passes through that solenoid.

My jumper wire is made with #8 wire . I actually have the jumper wire attached to one large terminal and the other end of the wire I have a heavy duty rubber boot over the coonector and zip tied up out of the way all ready to connect to the other large terminal if needed .

[Zepman]

I'm poor on electrics, Please can you guys advise how the solenoid works and how to jump the solenoid? and do you have to disconnect the battery -ve before connecting the jumper?

My limited knowledge and wiring diagram makes me think that turning the ignition key provides power to the solenoid via the hot switch wire 21, this powers the solenoid's electro-magnet and it has a plunger that 'closes' the circuit between the big posts, wires 39 to 36, in turn providing power to the fuse box.

My wiring diagram shows wire 39 to solenoid from battery is on a 3/8" ring post (big one). And wire 36 is the hot to the fuse box, also on a big 3/8" ring post, both these are I believe #13 guage wire.

So bridging (39 to 36) as Jack advises, with guage 8 would bypass the solenoid and provide power directly to the fuse box and I guess you'd need to disconnect it after shutting down.

I assume a faulty solenoid doesn't respond to the power coming from the ignition switch wire 21, either through a break or faulty internal wiring not activating the electro-magnet.

[knockdolian]

A solenoid is an electrically operated switch. It allows you to operate something with a high current like the starter motor with a small switch. It works by a winding which produces a magnetic field when you hit the start button. This field moves a plunger in the solenoid with a big plate on it. That will connect the two big posts together inside the solenoid. There will be two large posts one to the starter motor the other to the battery. You bypass the solenoid by connecting them to each other by either a pair of players or as stated a jump lead which must be at least the same gauge as the battery lead. Check that when you press the start button you get 12v at the solenoid on the small wire. You should disconnect it first and can check it with a test light or volt meter. You will only need to jump the solenoid until the engine starts then disconnect it as the starter motor will still spin with the engine running. The two big posts won’t be fused and you will need the battery connected. You will be able to spin the engine with the ignition off by bridging the big poste. It won’t however start as with ignition off there will be no power to the distributor. Hope this helps

[Imzz4]

I had put the relay in with the silver contacts . But just a few days ago , at night, I lost all power 3 times in about 5 seconds while rolling into 3rd gear. After that strange episode, it was fine and we came home with no problems other than my brain wondering what the heck was up now.
As it turned out, in its short life, the "film" on the one contact was high enough in resistance to prevent any current flow into the copper disk. The contact on the load side was still new looking as was the disk. I barely scraped the surface with the meter lead, and I had a good reading.
I put the other relay back in ( w copper contacts), and its back to working fine.
All the connections were clean and tight too. It's just one of those things .
Jack , I like your idea of making and keeping a nice jumper in the trunk. ( and , if i do, it will never happen again !)