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1985 GL1200 LTD
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Discussion Starter · #1 ·
At some point this weekend when I get off my lazy butt, I'm going to tear the front down again (just did timing belts last weekend) so I can troubleshoot my coolant temp gauge. I'm looking at the circuit (attached). I've never really looked much at these. Since my fuel level works, I can supposedly skip from the S198 point to ground. (page 114 of the electrical manual). Where I get lost is between there and all the way to the dash. I understand there's a green and black wire, but from where to where? What is C75 (6-Red). From there I can tell I'm following a green/blue wire from the sensor to the dash. Am I checking for resistance? Continuity?

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1985 GL1200 LTD
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Discussion Starter · #2 ·
Follow up. That coolant temperature sensor: is that this? Or is there something else along the circuit that I should be looking for? How do I test this?

326984
 

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Discussion Starter · #4 ·
put it in boiling water,

found this on the 'net


The ECM side of the sensor:

Connection: Yellow/blue — Green/red
Standard: 2.2 – 2.7 k ohms (at 20°C/68°F)

The gauge side of the sensor:

Temperature 80°C(176°F) 120°C(248°F)
Resistance 47 – 57 ohms 14 – 18 ohms
perfect. Thank you. That look like the right thing? I’ve now seen that there’s a thermosensor and a thermoswitch. I’m gathering that the switch is for the fan and the sensor is for the coolant temp gauge. Correct me if I’m wrong please.

with those assumptions in mind, is the sensor the one behind the thermostat?
 

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Piaggio MP3, was 02 GL1800
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oops,
I just realized I posted the gl1800 sensor readings.

this is what you should use, sorry about the mixup.
 

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Piaggio MP3, was 02 GL1800
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perfect. Thank you. That look like the right thing? I’ve now seen that there’s a thermosensor and a thermoswitch. I’m gathering that the switch is for the fan and the sensor is for the coolant temp gauge. Correct me if I’m wrong please.

with those assumptions in mind, is the sensor the one behind the thermostat?
look at that PDF,
it is hand drawn, but what you have looks to be right.
 

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Discussion Starter · #7 ·
look at that PDF,
it is hand drawn, but what you have looks to be right.
Ok yeah it's starting to make sense. The last piece (I think haha) is that wire coming from the sensor hot to "space..." Where is that going? Just to the gauge on the dash? The spot that says "G/Br." Is that wire color?
 

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Follow up. That coolant temperature sensor: is that this? Or is there something else along the circuit that I should be looking for? How do I test this?

View attachment 326984
That is the fan switch, the gauge sensor is just behind the heat shield. It looks like you have the ETM, just scroll down a few pages and there are pictures showing where things are.
 

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Discussion Starter · #9 ·
That is the fan switch, the gauge sensor is just behind the heat shield. It looks like you have the ETM, just scroll down a few pages and there are pictures showing where things are.
The ETM I have definitely doesn't have the pictures. I've seen it on another post though so I think I have the idea.

So, I'm reading this schematic and trying to follow the wiring around the bike so I have an idea of places I'm looking. There's a connector C57 that is referenced 36 times in the ETM. Not a single picture of it. It says "on left side of fairing." Interesting note. The guy I bought it from said the previous owner had a hell of a time connecting an aftermarket stereo and sure as ****, I found a crap ton of cut wires under the left pocket. Wouldn't be surprised if that connector is around there somewhere, and this is the culprit.
 

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1987 GL1200 Interstate
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Just a note. The aftermarket switches are not a good idea. There are thread size problems on some and temp rage issues on most.
Just sayin'...make sure your old one isn't working before you buy something.
 

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Discussion Starter · #11 ·
Just a note. The aftermarket switches are not a good idea. There are thread size problems on some and temp rage issues on most.
Just sayin'...make sure your old one isn't working before you buy something.
thanks for the warning. This is one of the reasons I’m trying to learn this schematic. If I can put it on a broken connection somewhere else along the circuit then I don’t even have to break the whole thing down again. Just trying to make sense of what I’m looking at in the ETM.
 

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The ETM I have definitely doesn't have the pictures. I've seen it on another post though so I think I have the idea.

So, I'm reading this schematic and trying to follow the wiring around the bike so I have an idea of places I'm looking. There's a connector C57 that is referenced 36 times in the ETM. Not a single picture of it. It says "on left side of fairing." Interesting note. The guy I bought it from said the previous owner had a hell of a time connecting an aftermarket stereo and sure as ****, I found a crap ton of cut wires under the left pocket. Wouldn't be surprised if that connector is around there somewhere, and this is the culprit.
This is the one with C75;
326988

I have not been able to find C57 either.
To check if the wiring is good to the sensor use a long thin probe of some kind and push it in under the intake on the right side and ground the grn/blu wire connected to the sensor, with the key on the gauge should go to hot, do not keep it grounded for any longer than necessary.
 

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Discussion Starter · #13 ·
I have not been able to find C57 either.
To check if the wiring is good to the sensor use a long thin probe of some kind and push it in under the intake on the right side and ground the grn/blu wire connected to the sensor, with the key on the gauge should go to hot, do not keep it grounded for any longer than necessary.
Brilliant. Just want to clarify what you mean by "push it under the intake on the right side."
 

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Brilliant. Just want to clarify what you mean by "push it under the intake on the right side."
The only way to get close to the temp sensor without taking things apart is under or just in front of the #1 intake runner. If that works try grounding the green wire, the problem could be on the ground side.
 

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Discussion Starter · #15 ·
The only way to get close to the temp sensor without taking things apart is under or just in front of the #1 intake runner. If that works try grounding the green wire, the problem could be on the ground side.
I'll have to look that part up regarding intake runner. Thankfully, I think I can rule out ground side. ETM says if fuel gauge works, I'm good at ground. Unless I read that wrong too.
 

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I'll have to look that part up regarding intake runner. Thankfully, I think I can rule out ground side. ETM says if fuel gauge works, I'm good at ground. Unless I read that wrong too.
You didn't read it wrong but there is still another connection (C75) between the sensor and the ground that wouldn't affect the fuel gauge.
 

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Discussion Starter · #17 ·
Got it. So I’m still kinda lost on the probe to the #1 intake thing. But, assuming I tore it down anyway, could I replicate that same test simply by shorting both plug pins together? Of course just briefly. Would that make it cap the gauge?
 

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Got it. So I’m still kinda lost on the probe to the #1 intake thing. But, assuming I tore it down anyway, could I replicate that same test simply by shorting both plug pins together? Of course just briefly. Would that make it cap the gauge?
Yes it would, I'm just trying to help keep you from tearing things apart to do a simple test, maybe. I don't know if you can see that sensor without removing anything but I assume you can. The #1 intake has nothing to do with it other than the sensor is in behind it.
 

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Discussion Starter · #19 ·
The #1 intake has nothing to do with it other than the sensor is in behind it.
I appreciate it. This here now makes sense lol. I was thinking what the hell am I supposed to do with the intake. I was over-thinking it. I'm digging into this tomorrow so just trying to be as theoretically prepared as I can. Pressure washing and yard work today.
 

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Good morning. Been following this thread. Post #1 is querying C75, post #12 clarifies where C75 is. The green wire is from the coolant temp sensor. This sensor is just for the engine temp reading on the dash. C57 is the 13 pin connector that plugs into the left side side of the front fairing. There are only two 13 pin/wire connectors on my '85 Limited Edition. The white 13 pin/wire connector just in behind the dash. The other is the black connector that plugs into the left side of the front fairing from the wiring harness. Think the ETM is wrong - C57 is not white, it is a black connector. These are the only two 13 pin connectors on my '85.

You mention "G/BR". Looked at page 114 and cannot see this indicated. Wire colour codes are the ones with a forward slash.

This is a picture of the thermostat housing and sensors.
Vehicle Motor vehicle Automotive tire Automotive fuel system Automotive exhaust
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.

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.

To get at Tw, I would remove the right side CFI and IAC valve covers. You can remove the hose that is between the IAC valve and the air chamber with long nose pliers. You may want to disconnect the IAC valve from the bracket as well. Do not remove the two small diameter size hoses from the IAC valve or you will be emptying the coolant system. You should be able to see the Tw sensor from this vantage point. Recommend buying a 12" set of needle nose pliers, very convenient for a lot of the work on these. Should be able to disconnect the Tw sensor wiring from here. The better way to test Tw is to disconnect the blue connector that is located under the shelter on the right side with the other connectors, page 118 photo 10 shows the collection of connectors I mention.

Hope this helps.
 
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