M.Unit / Fan wiring

[jakeh912]

Hey guys,

I have seen where a few others have wired in an M.unit and I wasn't able to find much on how the Fan and thermo switch are wired in.
I recently finished up, or so I thought, the wiring of the M.unit on my 87' GL1200i. The bike fired right up with no issues. The only major concern I had was the fan kicking on once it reached temperature. I let it idle and ran it until I thought it was at/above temperature for it to kick on, and nothing. Since then I pulled the plug on the fan and straight-lined to it and the fan does turn on. Before I pull the Carb to check the sensor I figured I'd see how people wired theirs.

Right now my wiring currently is: Per the Haynes manual, I have the (Green) from Thermo Switch to ground. I have the Fan motor (Blue/Black) to the Aux 2 output. I have the (Blue/Red) to the M.unit Breakout box B which is wired to my Moto-Gadget Pro. The (Green/Blue) is wired to the Breakout box B as well.

All advice is welcome, All your post on my build have helped tremendously!

[gltriker]

Scroll down this page to 'Similar
Topics.'
I see one listed there titled:
M- unit wiring

[jakeh912]

Hey GLtriker,

Yes, I actually have read that thread and many others. It doesn't address the issue I have with the Fan. Which is why I made a post.
With most of the posts being a year + I thought this would be better than resurrecting(commenting) on a post.

[gltriker]

Understood

[Rednaxs60]

From the OEM Electrical Troubleshooting manual, schematic of the original wiring:

Rad fan schematic .JPG

You need 12 VDC in and the rad fan temp switch grounded. My thought is the M-unit provides a 12 VDC power supply and keep the original rad fan temp switch grounded as per original. The manual does not show any BLU/RED or GRN/BLU wires.

You can do a cursory check of the fan operating temps with a small heat temp gun at the radiator. The rad fan should come on at approximately 80/85 degrees C and off at approximately 76 degrees C.

Good luck.

[jakeh912]

Thank you Red!

What I have is from the Haynes manual.

GL1200 87' main page 2.png

Which is nice for the color coordination and so far they have been accurate.

I did some trials today and took a lead and stuck it in the connection and grounded the wire and the fan instantly kicked on. So I do believe its a (Me not wiring something correctly).

Ill have to get the Heat gun trick a shot!

[Rednaxs60]

Same circuit, 12 VDC in and grounded through the thermo switch, no other wiring required. Just need to have the 12 VDC to rad fan fused, 10 amp fuse.

[Rednaxs60]

FYI, a schematic I used to install a manual rad fan switch, works well:

Rad switch schematic.jpeg

[jakeh912]

First off, Thank you, Rednaxs, for the help. I'm really trying not to throw in the towel and just wire it to a switch. Because of that, I have to really pay attention to my temps.

That being said I still very much have the issue of this darn fan not turning on. I have done a few things since the last post.

I removed the OEM Thermoswitch and cleaned it as to the guide found on forums and was simple enough. I bench-tested it in boiling water and nada. So I purchased a new Thermoswitch and same thing (it was a Chinese Thermo).
My shiny new from Japan Tour Max Thermo came in today and tested it in the water and nothing, I was doing some looking and people suggested taking a small propane torch to hit it up to test. Low and behold it worked and I Heard it click over and it showed continuity on the multimeter. To humor myself I tested the other two as well, the OEM(OG thermo) worked as well and the Chinese never worked.

I put the New Tour Max Thermoswitch in the plug and left the radiator off to then just test the wiring I put the torch again to the thermo and "BAM" the fan came on. All is good..... NO, I got everything installed and fired the bike up it comes up to temp and beyond and its still is not cutting on.

I have a few videos but was unsure how to get them on here.

Any suggestions are welcome.

[Rednaxs60]

I would disconnect the rad fan from the M-unit. Is the M-unit controlling the rad fan ON/OFF, or just providing a 12 VDC power source? The original rad fan circuit is a switched 12 VDC supply through a fuse through the rad fan to the thermo switch. The thermo switch closes and grounds the circuit at the appropriate temperature, ergo, the rad fan starts. When the engine coolant temperature cools to approximately 92 degrees C, thermo switch opens, no more ground, rad fan stops. Not sure of the open/close for the thermo switch, but

Have reviewed some videos regarding the M-unit. Have you wired the rad fan to an output and not an input - just want a 12 VDC power supply? Would make a difference.

Good luck. Cheers

[jakeh912]

I do have it wired to the M-unit Aux 2 Output which gives constant 12. I've checked the Black and Blue/Black and have a steady 13V's.

The weird thing is is that it worked when I didn't have the Thermo switch installed in the Bike. ( I had the everything on the bike and wired exactly how it would be on the bike and had the plug on the thermoswitch and bumped it with a torch and it kicked on.) I then installed the switch and let everything come up to what I believe is well above temp and it never kicked on....

I'm heading out to the shop now and I'll try just having it off the M-unit and just on a Steady 12vdc on the hot terminal.

I have two videos I'd like to link but unsure how.

[jakeh912]

Quick update:

Tested it wired straight hot and no luck.

I did test the (OG) Oem thermoswitch I pulled out that I have since cleaned. It tested find with the torch but wanted to see the temp it flips on at. I filled a Jar with some motoroil and heated with a heat gun. The switch flipped over at roughly 300F which is WAY high.

[dontwantapickle]

Please excuse the ignorance, but... what is an M-unit?

[jakeh912]

Hey no worries, So the M-unit (easiest way for me to explain) is like a Hub for everything. It eliminates the need for fuses (they're all built in). Also allows for an easy way to troubleshoot and track data(maintenance) etc. In my case it also allowed me to simplify the wiring since Im "cafe'ing" this bike and don't need 75% of the wiring that was on it.

[wingrider]

Please excuse the ignorance, but... what is an M-unit?

This may help you.