There are two types of sensors for the temp light...
One if for digital dash...the other is for the individual bulb type lights...
Both are just thermal switches...both switch at approximately 238F...
They appear the same...the difference is that one version is normally open...the other is normally closed...
I could have it backwards but 99% sure that the bulb type is normally open...
In both cases the switch provides ground...
So if I am correct the ground is normally present for the digital dash...and when the lead is disconnected it is the same as the switch going open...the logic circuit in the dash senses no ground and applies 12v to the led...
With the bulb...ckt is normally open...switch provides ground when it reaches 238F...completes ckt for bulb...bulb lights up...so in order to test it...you have to ground the lead...
A good gauge is the way to go...most gauges will use a 1/8 npt sender...
The oem threaded hole in the head is 1/8 bst...
One is 27 tpi...the other is 28 tpi...and the bst has way more taper...
You can thread the 1/8 npt sender into the bst hole...it will seal...it can hold 125 psi...
However, DO NOT try to tap the oem hole to 1/8 NPT... it will destroy the threads...then it will be a problem to seal with either threaded sender...
The soft brass threads on the npt will conform to the bst theads...teflon tape or sealant will do the job...
DO NOT OVER TIGHTEN IT... it will only thread few threads... that's enough...it will be re-usable for the oem sender too...no problem...
The I like to use the lead for the oem sender for the gauge...cut the lead from the harness under the dash and run to gauge...
If you have a digi-dash you have to ground the left over lead in the harness going to digi-dash as said above to keep light in digi-dash from coming on...
Done...
IMO...the best temp gauge for the rhino is a Gaffrig marine gauge... 270 sweep... 100 to 240 scale... resolution is perfect...working range is needle more or less straight up...
http://www.gaffrigperformance.com/Products/gauges.cfm?theSubCategory=35
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