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3 pin Temperature Sender

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ST2W nephews engine, no gauges work, he has a Thornycroft panel but nothing is connected. On the outlet manifold on engine he has what looks like a 3 pin temperature sender, I suspected a live, a resistored feed to go back to the panel & a NO switch which closes on hot to put a light on the panel. However putting a meter across all 3 pins in any combination I get no readings at all.

So does anyone know if my assumptions are correct, have a wiring diagram for it & finally where are we likely to get a replacement?

it might be that one pin is 5vdc power supply
one of the other pins sends back a variable voltage based on temp
the remaining? ground maybe?

got any pictures of the sender?

bob g

For the cost of a new temp gauge I would replace what you have and use a standard car style one. My preference is always a mechanical gauge as they tend to be more reliable and no electrics other than a light in the gauge. Obviously electric ones can be installed as a complete unit and then the connecting of the wires.
Either way remove the fitting from the manifold and go to the spare parts shop and match the thread size and pitch. This will be the simplest and quickest way to have a gauge working.
Is there any wiring in the dash board? If not best to start from scratch from my experience with electrickery. I could have spent hours tracing old wires on the Vintage David brown 30C tractor but instead bought the colours required and made my own harness in far less time. Plus I now know all the wires are in good condition with no fractures or corrosion.

I have only a very poor image of the sender, I was leaned over a running engine I should have checked it & realised how poor it was.

This is the panel that is in the boat, but we're not sure if it has ever worked with this engine as the anecdotal history says the engine was replaced with a recondition one around 5 years ago, but we don't know if it was of the same type or not.

But nothing works on the panel apart from the stater button & the ignition warning light which is just floating in the back of the panel.

I think as suggested the obvious answer is to remove the existing sender & gauge, by a matched set & get a convertor to go from the large current thread to a more usual one, somebody has suggested it might be 5/8th UNF is that likely?

Yes it is likely but I don't think BSF will be the thread for a plumbing fitting. I am not familiar  with your type of sender so it would be best to remove it and the oil pressure sender and match a pair of gauges up and install the new ones.
Does the tacho work and is it electric or cable driven?

Is best' to measure it to be certain. The pic unfortunately is not a lot of help.


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