Repair a Fan Switch

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Mark King
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Repair a Fan Switch


Post by Mark King »

You might be able to repair your current fan switch by simply cleaning it with vinegar. Especially in older bikes that sit, or have sat sometimes for years, the switch can become gummed up and stuck.

The switch is actually three pieces and the end cap is removable.

Because this part sits in the coolant it attracts the same gunk that plugs your rad.

Easy step by step process - and I'll add pics below when I remember how to do it.

1. After the switch is removed from the bike it is best to soak it for a few hours in a straight vinegar bath. This helps break up any corrosion that has accumulated on the threads that hold the end cap.

2. Firmly grip the main body of the switch - I used a hand held pair of vice grips where the wrench would normally go.


4. Underneath this end probe, there is a small and very short shaft and then a slightly larger piece. In profile there are eight distinct sections of the switch. You are looking for the third distinct piece counting the end probe as number one. (Shown better in the photos)

5. Grip this third section with a needle nose vice grip and turn it gently to unscrew it. It will take some effort but not much. If you are stripping metal off it like I did at first, it probably needs to soak longer.

6. Once the end piece is removed you will see a pin that is supposed to slide freely inside.

7. Soak the end piece with the pin in vinegar overnight and it should loosen enough to pull the pin out. If not, let it soak some more.

8. When the pin is removed, use your fingernail to scrape off any more residue that may be stuck on it and clean out the hole where it sits. I used a toothpick and vinegar bath.

9. Once clean, the pin should slide very easily in and out of the hole.

10. Re-assemble.

11. Test, or not, to suit but should probably test as this will only work if the switch is broken because the pin is stuck.




Hope the pics attached ok. If not I will add them again later.
Last edited by Mark King on Tue Aug 23, 2011 3:40 pm, edited 1 time in total.
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Re: Repair a Fan Switch


Post by sunnbobb »

I'll be dad-gummed! That is a fine little tutorial, thanks bunches!
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Re: Repair a Fan Switch


Post by Roady »

I had no idea ...

Worth trying on the old one (which never got thrown out, of course).
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Re: Repair a Fan Switch


Post by JBz »

my experience is the bottom contacts stay good. The top piece with the powdery stuff in it goes bad or collects moisture past its special seal and messes things up like the sliding pin. i cut one top piece apart in the lathe to take a look . If just the top part that screws out was available I imagine most could be saved. JB
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Re: Repair a Fan Switch


Post by The Subliminator »

Having some trouble on this very thing and I'm a long way from home. Does any one have part numbers for the automotive ones that fit?
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Re: Repair a Fan Switch


Post by ericheath »

roady did the research for this, i didnt see it here in this list so here is the link to his post. octane posted the interchange list and it will fit a bunch of gl's. ... 3965#63965
here is the link to rock auto
click on part number search
here is the part number
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Re: Repair a Fan Switch


Post by lt1 »

Doing the vinegar soak in combination with an ultrasonic cleaner may speed up the process.
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Re: Repair a Fan Switch


Post by Wingerinsandiego »

Great tutorial Whiskerfish! I am getting ready to check the temp sensor which is down line from the fan switch. Would be great to see a step by step on how to get to (right now I may have to remove the carbs) if it is repairable, etc. My temp guage is not working and this sensor is where hopefully my adventure ends. Thanks
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Re: Repair a Fan Switch


Post by fish »

mark thank you.
I just did this on a friends bike & it was a FIX!
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Re: Repair a Fan Switch


Post by djoyner »

I know this is an old thread, but I wanted to thank Mark for this tutorial. I picked up a '79 about a month ago and noticed that the PO hand installed a switch to active the radiator fan. I followed the excellent directions and the switch works great now.

Thanks onto rebuilding the carbs.
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Re: Repair a Fan Switch


Post by tlbranth »

Waaaaaaaah. No pics.
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Re: Repair a Fan Switch


Post by FrontRunner »

Great write up. I had a little trouble finding the right set of pliers to grip the part tight enough to break it loose. No needle nose vise grips to use so let's improvise. I scarred the thing up slightly with a few pairs of needle nose pliers and she would not budge. Looked around for something better and found a set of cheapo wire crimp/strippers that were actually the hot ticket for this. The screw driver is pointing at the part I used and is partially covering the marking saying "ignition terminals"
20180628_154651.jpg (108.05 KiB) Viewed 2146 times
As of now it's all soaking in vinegar.
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Re: Repair a Fan Switch


Post by salukispeed »

That portion on Those crimpers are for crimping on the old style spark plug wire terminals like we used to push down in the coil and distributor caps back in the day before electronic ignition, Old school stuff
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Re: Repair a Fan Switch


Post by FrontRunner »

If I'd have tried them 1st I might not have scarred the part up as much. I didn't hurt it with the other pliers. If you are doing this job and have those handy they work really well for this application.
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Re: Repair a Fan Switch


Post by Anthony Evans »

Thank you for the info. Mark King, great piece (also nice pics.) I have a painfully slow '77 project that I'm just about finished with myself in need of a thermo switch...gonna give this a try (seems like vinegar is the magic solution to everything) thanks again.
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