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Temp sending unit to Warning light

Rob Presley

New Member
Hi all. Im new to the site and very happy too have found you. I am in the process of making some cnc conversions in the shop and looking forward to the help I know Ill need.
On to today's problem.
I have built a custom Triumph 900 Motorcycle and as normal some aftermarket parts do not play well together. The Sending unit is a NEW Stock Triumph part, located in the head. The light we are using is mini led, simple 2 wire. When installed the light comes on and stays on through all functions. I believe this issue lies in the sensitivity of the led and the 20ga wire to the sender.
If I run a standard filament test light from the power source to the sending unit the circuit does not close and the tester stays dark. If I swap out the tester for the same led lamp if lights up and stays on. Since the sending units are potentiometer of sorts in that as the temp rises the circuit begins to close. At the designated temp the light comes on. I think the sender is always grounding at some minor value and the resistance of the small wire and led light is so low that the circuit is closing prematurely.
I may be all wet about this and need some guidance. We are committed the lights so I need a solution. All thoughts are welcome and appreciated.
Thanks Rob
Last edited:


Well-Known Member
Most Helpful Member
What "sender" is it - what function?

The simplest solution is probably a resistor across the LED lamp, to bypass any leakage current.

Can you connect a meter in series with it to measure the current when it's supposed to be off and when the lamp is directly connected to power? That would give a good idea of what value may be appropriate.


Well-Known Member
Most Helpful Member
Could the sensor just be a thermistor? A link would be helpfull.

Edit, what is it measuring the temperature of? Water, oil, metal.

Rob Presley

New Member
Thanks for your input. I looked at the packaging from the new sender and it offered no data about the product. I will get a meter on it today and report back. Ir the current leakage a constant or does it increase as the temp increases or is it on or off? Is it possible to increase the Resistance thorough wire size?
Thanks again. Rob

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