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Discussion Starter · #21 ·
This is a picture of the thermostat housing and sensors.
View attachment 327004
The front is the rad fan sensor, the middle is the coolant temp sensor for the dash readout, the rear sensor is Tw - the one in question.
Hey glad you came by the thread. So, to be clear on what I'm looking to do here: I have no indication of temp on my dash. That's what I'm troubleshooting. With that in mind, I'm still looking at the rear one for Tw?
 

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Discussion Starter · #22 ·
To check the rad fan sensor you can disconnect at the sensor and test in situ without following any wires to connector C75. To check the coolant temp sensor use C75.
As of right now, I have both lower fairings removed, radiator removed, and the 2 metal covers removed that hold the lower fairings on either side. I can see sensors in there, but it looks like it's behind a heat shield that engine mount bolts go through. Not sure if that's where I should be.

Honestly, it looks like at some point there were 2 wires coming off the sensor. I see the GRN/BLU one as indicated on the schematic, but there's clearly another one that was cut. I do not see that on the schematic. If I check C75, what am I checking and to where?
 

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Hey glad you came by the thread. So, to be clear on what I'm looking to do here: I have no indication of temp on my dash. That's what I'm troubleshooting. With that in mind, I'm still looking at the rear one for Tw?
Looking at the middle sensor. Check for correct resistance and continuity of wires at connector C75. If you want/need to get at the sensor, I'd recommend removing the heat shield located over top of the timing belt covers. Front upper motor mount bolts can be removed and put back in.

The wire at C75 is the green wire with the blue band.
Automotive tire Motor vehicle Bicycle part Bicycle handlebar Electrical wiring
Corresponding wire at connector:
Cable Gas Electrical supply Ac adapter Wire

To check the wiring to the dash, would recommend removing the wind screen to get at the 13 pin/wire white connector, and do a continuity check of the wiring from this connector back through to the corresponding wire at connector C75 - the green wire with the blue band.

Good luck
 

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As of right now, I have both lower fairings removed, radiator removed, and the 2 metal covers removed that hold the lower fairings on either side. I can see sensors in there, but it looks like it's behind a heat shield that engine mount bolts go through. Not sure if that's where I should be. Remove the heat shield for easy access to the sensor. You are in the right area.

Honestly, it looks like at some point there were 2 wires coming off the sensor. I see the GRN/BLU one as indicated on the schematic, but there's clearly another one that was cut. I do not see that on the schematic. If I check C75, what am I checking and to where? You are going to do a sensor wiring continuity and resistance check. There has to be two wires from the sensor connector into the system. See my photo above. If there is not remove the sensor connector, cut back the sheathing and see where the second wire is cut. If there are two wires at the sensor connector, do a continuity check of the wiring up to C75 as per my previous post. The green wire without the blue band can be checked at C75 green wire no band.
Hope this helps.
 

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Discussion Starter · #25 ·
Looking at the middle sensor. Check for correct resistance and continuity of wires at connector C75. If you want/need to get at the sensor, I'd recommend removing the heat shield located over top of the timing belt covers. Front upper motor mount bolts can be removed and put back in.

The wire at C75 is the green wire with the blue band.
View attachment 327007
Corresponding wire at connector:
View attachment 327008

To check the wiring to the dash, would recommend removing the wind screen to get at the 13 pin/wire white connector, and do a continuity check of the wiring from this connector back through to the corresponding wire at connector C75 - the green wire with the blue band.

Good luck
Thanks again for the detailed instructions. I don't know a whole lot, but I can follow instructions lol. What would you say is the correct resistance on that distance of wire? an ohm or 2?

I think and hope I found the culprit. Hoping I can rebuild this while maintaining some integrity of the boot. Picture is sideways. This is behind the heat shield. The other wire is just hanging out back there loose.

327009
 

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Definitely the culprit, no ground. Will look at my connector to determine if it can be modified, or you can pull the one side out.

The resistance check is for the sensor not the wire. Wire continuity is to make sure it is not broken anywhere.
 

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Discussion Starter · #27 ·
Definitely the culprit, no ground. Will look at my connector to determine if it can be modified, or you can pull the one side out.

The resistance check is for the sensor not the wire. Wire continuity is to make sure it is not broken anywhere.
I've got a half-assed rebuild on it. Going to put a larger heat shrink around the end I had to cut and silicone it. I tried to clamshell the end I cut but no dice.


327010
 

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The front is the rad fan sensor, the middle is the coolant temp sensor for the dash readout, the rear sensor is Tw - the one in question.
The TW sensor is NOT the one in question, his gauge is not working, that is the middle sensor.
 

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Discussion Starter · #29 ·
Ok, I'm almost ready to put things back together. Since I had to remove the thermostat housing to get the heat shield off, I'm wondering about replacing the thermostat oring. I didn't see that listed anywhere in parts lists that are floating around here and other forums. Looks like I can order OEM but it may not be here for a few days. Are there alternatives that are typically available locally?

Also, I don't have a good mental image of the clearance between the thermostat housing and radiator. Can you typically change the thermostat with the radiator still installed? If I can put this all back together now and put that gasket on later, that would be ideal for me.
 

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You might, maybe be able to find an oring locally but I would bet probably not, Honda uses typically smaller thicknesses than can be found on the shelf anywhere. Might be able to change it with the radiator in place but it would be tight.
 
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Discussion Starter · #31 ·
You might, maybe be able to find an oring locally but I would bet probably not, Honda uses typically smaller thicknesses than can be found on the shelf anywhere. Might be able to change it with the radiator in place but it would be tight.
then I’m going to play it safe and just wait. I’m not trying to do this tear down any more than I have to.

so I’m about to wrap up for the day then on that note. I ended up getting a new thermostat from NAPA while I was in there. And their radiator hose that I cut to fit both upper and lower. I appreciate y’all walking me through this stuff as I go.

Oh, for electrical sealant I ended up going with a liquid electrical tape. It’s non conductive and makes a nice thick seal around that cap where I cut it.
 

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Thermostat cover o-ring: 91307-MB0-003 size: 54X2 mm. Contact a hydraulic shop. As long as the o-ring is "proud" of the groove in the thermostat cover, an o-ring with a slightly smaller thickness will work. Less expensive at a hydraulic shop.
 
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Discussion Starter · #38 ·
Thermostat cover o-ring: 91307-MB0-003 size: 54X2 mm. Contact a hydraulic shop. As long as the o-ring is "proud" of the grove in the thermostat cover, an o-ring with a slightly smaller thickness will work. Less expensive at a hydraulic shop.
Thanks for that. I did end up ordering this one and one for the water pump cover from partzilla. Shipping was more than the o-rings.
 

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This is the web site I use for parts lookup: 1985 Honda GL1200L A OEM Parts, PartsPitstop.com

Most o-ring sizes are listed with the P/N. I contact my local hydraulic shop first before ordering from Honda, less expensive. Same with bearings.
 
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Discussion Starter · #40 ·
Coming back to this real quick. I'm waiting on my o-rings from partzilla still. Probably could've had them already from another source but I'm alright. Anyway, I took the thermosensor out today and measured resistances per the manual. Works just fine. Question is: there was no o-ring or anything on this thing when I took it out. Should I put something on it?
 
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