Hey kids, got another one for ya. Probably applies to all liquid cooled bikes. This one's a '93 Vulcan 750, if you must know.

My problem here is that the fan stays on ALL the time. Even when the key is off. If you just leave it sit, it kills the battery. The temperature sensor reports proper coolant temperature, so I don't believe that is the problem. I'm thinking the only other thing it could be is the fan relay is stuck closed, right? Looking at the service manual, it says its in the junction box. Do I generally have to replace the entire box, or is the relay usually a separate part? The bike isn't at my location, so I'm trying to cut down on the running back and forth to stick my nose in it.

Here's the service manual, for those of you who want to play along at home:

http://www.tocmanufacturing.com/File...nd%20Parts.pdf

 

Sounds like you got it nailed down. As long as it hasn't been modified somehow. You never what people do to their bikes.

The relay should be able to be unplugged from the junction box.
I would unplug the relay and test the pins with a multi-meter. Make sure there isnt voltage making it to the relay before you buy another one. You should have a full battery power supply, and a signal supply. For your test, there should be battery voltage on the main power in, but not be any signal voltage, if there is, there is another problem somewhere else.

 

Woah. . .that made surprisingly little sense to me. Are you talking about signal relays up there? I'm talking about the fan relay. Anyway, do I have this straight:

Pull the relay and do a continuity test on the pins. I should have continuity on one pair (the electromagnet side), and no continuity on the other (the switch side). If I have continuity on both, then the relay is stuck closed, and should be replaced. If it tests good, then I am most likely getting power from the fan switch (the temp sensor in the coolant) even when the coolant is cold, which means the temp sensor is bad (this is unlikely, as the temp gauge is working properly). Correct? What if the relay is good? What do I test, then?

Wait a minute. . .are the fan and signal relay in the same assembly? I only see a turn signal relay in the parts list:
http://fiche.ronayers.com/Index.cfm/...ical_Equipment

 

sorry, I should have clarified what I meant by signal supply. On the relay, you have a constant voltage from the battery. The signal supply, is what triggers the relay to close and open. The signal will come from the sending unit. If you have the signal voltage, that means there is a supply voltage responsible for triggering the relay, and not the fault of the relay.

Personally, I would just use a the volt setting on your multi-meter to check the pins. You should have one reading around 12 volts, and no voltage on the supply wire. If there is a signal voltage, (usually very low voltage, around 1 or so), then you have an issue before the relay, probably the temp sensor.

Just out of curiosity, did you unplug the temp sensor to see if the fan shut off?

 

Nope. I assumed it was good, as the temp guage was giving a proper reading. The only method I knew of testing it was dropping it in a hot pot of coolant, and I was trying to avoid all that trouble if I was fairly certain it was good, anyway. That's a good point with unplugging it, as it sends the signal to the relay. I'll give it a shot.

Any idea why I can't find the relay part#?

 

wow, after looking at the schematic a little closer, I think your right about the junction box and the relay being one. It appears the juntion box has a relay built in. So, it doesnt look like a simple relay to unplug and replace. the junction box is the only thing between the fan and the sensor.

having said that, if it is the junction box that has to be replaced, and I have no idea how much one would cost, but if its expensive, you can re-wire a relay in its place. A universal realy can be bought for about 5 bucks at most autoparts stores. I think I would consider bypassing the junction box altogether and put in a relay. Unless of course the junction box is cheap, then obviously I would just replace that.

And that might explain why a part number doesnt exist for it.

so, disregard most of what I said in my earlier post.

 

SO, I connected the battery so I could get the juice flowing and start testing where the "leak" is. Fan switch (temp sensor) in the radiator tests good electrically. I pop the side panel off to get access to the junction box, and I rap it a few times with my knuckle while explaining to someone that the relay is inside there, and that's when the fan shut off on its own. I fiddle for a bit, and assume that the relay was stuck and hitting it unstuck it. I tested the relay electrically, and it's good. No odd power output. I started the bike and drove it a few miles; making sure the fan turned on and off at the appropriate temps. I gave the box a good whack with a screwdriver handle to be sure, and declared it fixed (with the warning that it might stick again, at which point we'd replace the $120 part).

So I get a call the next day. The owner was cleaning some dried battery acid out of the area near the junction box (he had neglected to reinstall the battery drainage hose when he pulled it for recharging, and I told him to get some compressed air and blow it out), when the fan started running for no reason again (the bike had been off overnight at this point), and THE BIKE ATTEMPTED TO START UP ON ITS OWN. The owner confirmed the ignition key was OFF, pulled the battery terminals off, and called me.

I went down there, and the junction box starts buzzing and vibrating as soon as you connect the battery. If I disconnect the 10p connector that powers the fan and other accessories, the buzzing stops. I noticed the output on the fan relay was 6v (should be 12), and 12v is definitely getting IN to the box, but not out. Diagram says it's pretty much battery - fuse - fan relay (no R/R) so I'm replacing the box.

I tested the R/R anyway, and all the resistances are correct, but I get 0v out of the Monitor pin. Is this normal when the bike is off?

 

Update: I cracked open that junction box and it was loaded with corrosion and half the traces were lifting. Ordered a new one.