got a quick question I want to put an override switch for the cooling fan I've done a search and found a couple of diagrams on how to wire it in question is my bike is a 16 valve 91RS does it wire in different than on the 4 valve and if so does can anybody tell me how to wire it in thanks

Currently, there's fairly complex thread going on the forum about a (I think) similar bike with fan circuit questions.
The short answer is YES the two are different. You can view that thread Here:
https://www.k100-forum.com/t6076-overheating#69239

As I recommended strongly to this fellow......Please do not add a fan switch.
(Other users here have a different opinion on this subject)
You should locate whatever failure is causing your failure with the fan & fix it correctly......then if you have it all working and you still want a switch, it's still your option.
Personally, I would like to know the following from you:
If you dis connect the coolant temperature sensor at the top left front of the engine (behind the radiator and injection throttle body) .....and turn on the ignition switch, does your fan start.
I don't want you to tear the bike all apart to answer my question, but if you have access, I'd like to know.
Regards, ibj....

The bike works fine it's just that it's getting hot here in the south west and I have a switch on a 85 that I have I like it when I get into stop and go traffic I can turn it on and the bike never gets hot it's just an option that I like

I live in Phoenix, AZ It was 102 deg when I got home from a ride last week. The bike was preforming normally and the fan did not start. I have seen it run when it gets to the correct parameter.
My 85 rs is stock. The fan comes on occasionally as designed when needed to keep the temps within the designed levels.
You can certainly do whatever you think is right.
My logic seems that you could be trying to prevent the bike from running normal by attempting to overcool the radiator when it isn.t required.
I do understand your concerns.
For all my years as a professional fleet mechanic.....I have often had a very difficult time changing peoples pre-conceived notion of what "Hot" really is.
I think this often occurs from some paranoia about viewing a temperature gauge, although our 85's don't have a gauge When it's cool/cold outside....the temp will run at exactly whatever the thermostat allows, throttling coolant flow as needed to keep the engine warm enough. In warmer weather, once the thermostat is fully open the temp will often run higher than what people are used to seeing as "normal" (but still well within designed range). Since it's now running hotter than "normal" it's often viewed as "overheating" when it in fact is not.
People will jump through all kinds of crazy hoops attempting to keep that temp at the "bottom" edge of the normal range. A colder thermostat is often tested/installed. The end result is that in cool weather, "normal" is now cooler than it was.....but in hotter weather, once the thermostat is again fully open, the temp again climes to a hotter end of the range before stabilizing.
I am not saying that the example is your situation........just proposing some points of view.
Regards, ibj...

I believe that you could use a switch to interrupt one of the 2 wires to/from the temp sensor to start the fan but that would cause issues with the Fuel injection drivability.
Someone else here will be able to tell you how to switch-trigger the fan control relay to get what you want.
If you re read the thread I linked to you earlier.....I think the needed info is in there somewhere where they talk about that user's fan relay wiring.
Good Luck. I'll see you in Salem on July 17!
Regards, ibj..

your exactly right about fixating on the gauge on one of my airheads when I bought it the guy had put one of those oil temp dipstick gauges in I couldn't keep my eyes off of it so I got rid of it and never regretted it thanks

If you do put a fan override wsitch you need to make so that it operates the relay directly. Some here have made it so it puts an earth on the wire to the ECU and it does make the fan come on but the ECU thinks the engine is massively over hot and if you stop the bike it will not start unless you turn the switch of but when you make the relay operate directly then the ECU doesn't even know what is going on and it wont have any effect on what it does.
The 16v engines are to be done the same way by switching the relay on directly.

I am 100% with ibjman if there is a problem fix it if there isn't and the fan still comes on when it gets to the switching temperature then don't worry about it just ride it
Regards,
K-BIKE

I tested my fan on road yesterday....made a 50 mile round trip from West Phoenix to Mesa & back to pick up some woodworking supplies. 102 Deg F. outside. I am amazed at how seldom the fan seems to be needed even when getting off the freeway and idling at a stop light.
 It did come on a couple of times on the way home when waiting at a light to turn left back on to the freeway.

 I found it strange that as I listened to it humming away, I could hear it's speed change up & down in unison with the flash of the turn signal.......not sure if I have a problem or it's just that the fan is a big draw.
Regards, Ibj...

Thats normal the Alternator isn't charging when at the lights idling

RicK G wrote:Thats normal the Alternator isn't charging when at the lights idling

Starts at how many RPM RicK G ?

Usually it has enough output to keep the light from coming on but charging in any real sense wont start till about 1500rpm and for checking charge voltage about 2500rpm will give a true reading.

Thanks, again...

ibjman wrote:As I recommended strongly to this fellow......Please do not add a fan switch.
(Other users here have a different opinion on this subject)
..
Regards, ibj....

ibj, A counter argument is that at least for the K75's the fan comes on so rarely it's really nice to be able to confirm that it is working properly by hitting a momentary switch and hearing it. Several club members have had their fans fail at some point and never noticed the absence of the fan until there was a serious problem, i.e. radiator overflow in one instance. So far not been a problem for me but on several trips I've gotten up in there and flipped the fan blades around just to make sure they hadn't seized as I hadn't heard the fan in so long. Having a little momentary switch so that I could confirm operation sounds like a nice feature.

Agreed,
 If you feel the need to have a "test" switch for the fan....then a momentary switch would be my vote as opposed to an on/off.
However......you could put all kinds of extra switches on machine to test all kinds of items I suppose.
 For me......I've already added too much "auxiliary" wiring to my bike with an extra fuse panel, extra road lights with their associated switch, relay & harness, A set of headlamp relays & wiring, extra heated clothing power outlets (for GPS also) + a trick little flashing strobe in the front parking/running light, and a high altitude override plug switch assy. I scarcely have any more room or patience for yet another (un-needed) switch & wire.
Just sayin'.........Jman