Wiring diagram for Sigma-Tek 168BH-910-1LBW oil temp gauge

[PeterRus]

Sigma-Tek 169bh-910-1lbw.

Does not work until tapped. I am assuming some wiring issues in the dash. 

Does anyone have the wiring diagram for the gauge? There are four leads in the back, I am assuming two are 28V power +/-, and two are for the thermistor aka "oil temp probe". Is it possible to bench test the gauge?

TIA.

[PT20J]

From your description it sounds more like a mechanical issue with the meter movement than electrical. Schematic for connections to the cluster is in Mooney service manual for your airplane. Used gauges are available online. Sigma-Tek also overhauls these.

[PeterRus]

I suspect the receptacle in the back of the gauge may have a bad/dirty contact. Looking for pinout of the mating connector in the back of the gauge with acceptable values for each pin.

Found this: http://www.sigmatek.com/cluster_gauges.html, but it's for 6 pins on the back and different gauges. Mechanical issue with the needle is unlikely... 

[PT20J]

You could call Sigma-Tek. I found them responsive in the past. The cluster unit is easily removed from the panel and you can take it apart and trace the wires from the back panel connector to the individual gauge connectors. That's what I did when troubleshooting a fuel pressure gauge. The wiring from the back panel connector to power and ground and sensors is in the Mooney schematic. 

The cluster unit is well built and it seems unlikely that a wire broke. The individual gauges remove from the front by loosening the screw. That will give you access to the pins on the backplane and the gauge. Once out you can also take the cover off the gauge and see if the stop is sticky. D'Arsonval meter movements have an armature that rotates against the tension of a hair spring. When power is turned off, the spring snaps the needle against the stop. If age makes the stop sticky, it can cause the needle to stick. Sticking at the off position but coming to life when tapped is a classic symptom. 

[PeterRus]

Great, thank you for the picture and the details. The gauge is out and I removed it from the (aluminum) case -- all looks clean and manually moving the needle does not have any resistance/stickiness, the needle also comes to rest with grace when released. Other than the mechanics parts it has a few resistors and a zener. I am thinking if I knew the pinout I could supply power and with a variable resistor "test" the gauge.

I've filled out SigmaTek online form and will try to call them on Monday. 

[PeterRus]

Update: sent the gauge to SigmaTek and they confirmed issue "that the meter sticks. The unit needs a new meter and calibration".  $530.