how to install a fan switch 1987 k100rt - K-Bikes.com - Excellence in Motion
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post #1 of 11 (permalink) Old Mar 29th, 2014, 9:57 am Thread Starter
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how to install a fan switch 1987 k100rt

Hi I just purchased a very well used 87 k100 rt mfg 3 87
Ihave installed a used fan jumping relay box turn the fan on temp light lite when jumped
how ever after running the bike aprox 15 mnts no light no fan just boiled fluid the temp
light came on prior to changing fan rather than further testing I would like to hard wire the fan
with an on off switch and install a temp gauge a local parts place suggested putting the temp probe into the fluid drain plug ?? would like to not splice into wiring harness just a wire from fan to battery with a switch in between please advise of merits on this
thank you in advance
ps
I know this sounds draconian but when it comes to electrics I am challenged and replacement sensors are not existent ordering over the net from U.S is expensive

Last edited by uszacki; Mar 29th, 2014 at 10:51 am.
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post #2 of 11 (permalink) Old Mar 29th, 2014, 3:17 pm
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The good news is someone out there has a page on how to do this. The bad news is I no longer have the address.

But it goes something like this FOR A 1985 K100. Remove the tank to access the fuse box. Locate the fan relay. Pull the harness block with the leads off of the relay.

What I call the top will look something as follows. I am not sure if this is looking at the relay or the connectors on the harness side. I think it is connectors on the harness side but you get the idea.




If you turn on the power and run a wire between 15 and A2 on the harness side, the fan will run continuously. So, you must run one wire from 15 and one from A2 with a switch connecting the two.

As I dimly recall, I did this by using what I call the bottom, the side of the connector block with the wires from the harness:



I made two Y connectors. First, I pulled out the 2 Green/brown, attached one end of my Y to it, and then put one end back into the connector block. Second, I did the same with the Purple/Yellow. Pull out the Purple/yellow from the connector block, connect this to one end of the Y, and put another end of the Y back into the connector block.

I am adding two wires to the harness by splicing but without cutting the original harness. Connect the harness block to the relay. The fan will now run as original, but I have two wires running out of the harness from the motorcycle. If I connect them when the key is on the fan will run. Run those two wires to any desired spot, add a connecting switch and you are done.

You can make the Y connectors by crimping if you can't solder. You will need male and female connectors. I managed to blunder my way thru; so, you should be able to also.

Last edited by 97tiger885; Mar 29th, 2014 at 3:55 pm.
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post #3 of 11 (permalink) Old Mar 29th, 2014, 4:11 pm
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Another metod: Connect E (sensor) to ground to start the fan (the warning lamp will show and engine must be running, when using this metod).
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post #4 of 11 (permalink) Old Mar 29th, 2014, 4:40 pm
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Quote:
Originally Posted by IngeK
Another metod: Connect E (sensor) to ground to start the fan (the warning lamp will show and engine must be running, when using this metod).
Very nice. A warning light when you use the switch. I wish I had done it that way. Maybe I will change it the next time I remove the tank. Thanks for the tip.
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post #5 of 11 (permalink) Old Mar 29th, 2014, 5:21 pm
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The difference in the two metods is:
When connecting 15 & A2 you bypass the relay contacts which sends power to the fan.
When connecting E to ground you fool the relay to think that the engine is f.... damn hot.
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post #6 of 11 (permalink) Old Mar 29th, 2014, 8:29 pm Thread Starter
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Thank you all for your advice the reason i thought of running a wire from battery to fan
and operated by a switch was to keep it simple and eliminate having to remove the tank and side fairings if future problems occur with the relay switch is direct wiring a good idea
what are your thoughts or suggestions on how or where to install an aftermarket temp gauge
again thank you I have found this forum helpful in rectifying other issues
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post #7 of 11 (permalink) Old Mar 29th, 2014, 10:38 pm
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Quote:
Originally Posted by IngeK
Another metod: Connect E (sensor) to ground to start the fan (the warning lamp will show and engine must be running, when using this metod).
Won't you then lose any visual indication of an overheat condition?

Nick
1993 K75S
1991 R100RT
1982 Yamaha XJ650RJ Seca
1978 R100S
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post #8 of 11 (permalink) Old Mar 30th, 2014, 9:36 am
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Quote:
Originally Posted by stokester
Won't you then lose any visual indication of an overheat condition?
Yes, you do...if you're afraid that the engine gonna overheat even with the fan running
(this can of course happen, if you got other problems with the cooling system)...
choose the 15 & A2 metod, or add a temp. gauge.
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post #9 of 11 (permalink) Old Mar 30th, 2014, 9:46 am
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Quote:
Originally Posted by uszacki
install a temp gauge a local parts place suggested putting the temp probe into the fluid drain plug ??
On the K100's a temp gauge was standard on the LT and late RS models, a option on the rest.
And the sensor was placed in the coolant drain plug hole.
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post #10 of 11 (permalink) Old Apr 1st, 2014, 8:13 am Thread Starter
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Once again thank you all finally got the replacement fan to kick in still will add a temp gauge
it appears that the fluid drain plug is the best place any suggestions on any aftermarket ones that are reasonable and easy to wire in
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