Temp gauge full scale when head light’s are on…
I’m driving at low speed in town in the rain and I suddenly realise my engine temperature gauge has gone full scale. I pull in, fearfull of an engine sieze, thinking I have lost my coolant maybe or my oil pump, but everything seems ok. I go to kill the engine and just as I switch of the parking/city light’s (I alway’s ride with headlight on) I notice that the gauge returns to normal. I decided I had an electrical problem which was confirmed when I realised the high beam dash light was dimly lit when I had low beam selected and went off when I switched to high beam’s, while the head light itself followed the selector switch rather than the indicator (luckily enough). The indicator’s dash light seemed to work correctly as did the nuetral light. The engine appeared to run fine including kill switch and ignition switch. The day that was in it (raining pretty heavily) I blamed exposed connection’s in the loom and carry on.
I have a full wiring diagram (all be that it has already proven to not be an exact match on the colour codes) and the tool’s to test with, so I set too the next day in the shed. After following the wiring diagram I realise that the temp gauge, the full beam indicator lamp and the 2 clock backlight’s (which are on with the parking light’s) all share a common negative marked as B/W on my drawing. My first port of call is a connection below the petrol tank on the right hand side of the bike. It is a blue 9 pin plug which lead’s to the dash assembly. It is just visible beneath the yellow connection in the picture below. You don’t necessarily have to take off the tank to get at it as it is usually accessible from the rhs of the engine.
I found the negative at the socket (main loom side) was good and the connection itself seemed in good order on both the plug and socket, so I removed the dash from the bike as it seemed the problem was in the dash itself and you can’t access the connection’s to the dash while it’s on the bike. When I opened up the back of the dash I expected to find a looped negative between the four component’s involved but instead I find four seperate B/W marked wire’s going down the loom from the back of the dash but only one B/W wire comes out at the plug.
So it seemed likely to me that there was a joint hidden in the loom in between somewhere and sure enough after cutting away the outer sleeve and tape (apparently a previous repair to the outer protection) I found a crimped connection about 1/3rd of the distance down from dash to plug. Unfortunately the location of the joint mean’s it is about the middle of the section of the loom which is required to flex with the turning of the steering stock which is I’m guessing what lead to the breaking of these wires at the crimp. To fix it I shortened the four clock side wires back a little and I soldered them together with a new length of wire which I then joined to the existing wire coming from the plug furthur down so as to try to remove the joint’s from the flexing section of the loom. I Insulated the joint’s and retaped the loom. Back into the bike and everything is good again and the temperture guage is apparently (to my eye at least) reading just a shade lower than it used to.