Help FZR250 Temp gauge rises when lights are turned on?

I'll have to test that tomorrow after work sorry am home with baby and mrs now. Will update you as soon as possible.
Oh what should the battery read? That was with the ignition on -> lights on and off.

 

Mmmm I'd have to check that again tomorrow. I'm thinking there could be a bad earth in the lighting wiring somewhere.

 

OK looking at the schematic, the green/red wire goes to a 4 pin connection which goes to both the temp sensor and there's a thermo switch also in that thermostat housing also - correct

 

Just the igniton on with no lights on and engine off. Battery will typically read between 12.4 and 13.2V depending on state of charge of your battery.

 

That's a good point, all the more confusing without being able to see everything laid out in front of me. The green and red wire only goes from the sensor to the back of the gauge, I found this out only after I had wired a new wire in. The gauge is grounded from negative to the signal connections on the back of the gauge without any power to it, again only found this out when I had the gauge out. So with ignition on the gauge breaks the circuit so to speak?

If I may ask - if there was a bad or insufficient earth for the lights, would it find a way to use the gauge earth as an 'extra' path and in doing so cause more current through the gauge and a higher reading?

 

Yup I've connected the sensor wire straight to the battery negative terminal and reads full hot on the gauge. Drops to cold once I disconnect it.

 

Yeah totally agree the green with red stripe is the sensor wire, black is earth and brown is positive. Yeah there's already a hard wire fan switch - would that affect it though, I thought it would be completely separate.

 

That's an interesting question, with both the green/red and black wires from the back of the gauge, is there continuity between those two connections on the back of the gauge - to my thinking there shouldn't be as that would affect the gauge reading correctly

So the straight wire you ran directly to the temp sensor was from the green/red connection on the gauge to the sensor - correct?

 

I do know which wires are positive, negative and sensor in case I've been unclear.
I'll test the voltage at the gauge with lights on and off and report back.

 

Yeah there's continuity between the black(negative) and green/red(sensor) at the back of the gauge. That was my thinking but when power is applied there is no longer continuity. Without over thinking it I could imagine that's how the gauge works.
Yup I removed the green/red(sensor) from the gauge and ran I new wire to the sensor. I since tested the green/red and it only goes from the sensor to the gauge.

 

Would there be any harm in running a test wire from the negative wires at the head light plugs to the battery negative terminal and see if that eliminates the gauge jump?

 

OK, I was suggesting doing that test of purely the gauge internals, so with the wires disconnected

 

long story short - the gauge is reading too high and jumps up when lights are turned on, thought we had it sorted, however the problem returned when Brandon plugged the headlights back it

The issue is a secondary current path from the gauge sensor wire to ground, it isn't a direct short to ground, but allows extra current flow, which increases further with the headlights on

Apparently the thermo switch has been bypassed with a hard wire switch on the dash or thereabouts to switch the cooling fan on

 

Remove the dodgy bro's fan switch and make everything standard.

 

Yeah I’ll try unplugging the extra tail indicators and fan switch tomorrow. Tonight I’m going to try running an extra ground from the headlights to battery negative just so I know. The fan switch is wired from the original sender unit - the PO has unplugged the sender and put a switch in its place so don’t think that’ll do it but I totally agree with returning everything to standard.

 

So with that extra ground from one of the two headlight plugs direct to the battery negative the gauge no longer jumps when lights are turned on.
Would it be safe to assume either there’s a poor earth somewhere in the loom from corrosion or the PO wiring?
And would it be safe to run a new permanent earth wire from that headlight loom to battery?

 

There is the slightest rise on the gauge when lights are turned on but I’m guessing with a decent earth wire that’ll help?