Cessna cylinder head and oil temp gauge wiring

[Cardiff Kook]

Can anyone confirm if the top male spade connector (circled red) is power?

I had some work done under panel and I think the spade connector for power came off. I want confirm that is the spot for a power wire before I plug it back in.

Couldn’t find it in maintenance manual

 

[BC12D-4-85]

How many spade connectors or plugs go to your circuit board? Are the rest still connected? I assume the "SL" and "SR" spades are for the left and right gauges. The third is likely the power that runs through each gauge, then on to each grounded sensor (a variable resistor sensitive to temp) via individual wires.

Gary

 

[Cardiff Kook]

Not sure how many- there are ALOT of wires behind that panel. I was surprised

 

[BC12D-4-85]

There's lots of happy wires back there for good reason. To the gauge assembly I suspect three...one for power, and one each to either the cylinder head temp probe near the lower spark plug on one cylinder (marked SL on the circuit board above), and another to the oil temp probe (marked SR). That's assuming your gauge cluster is the same as the screen grab.

Just guessing here of course.

Gary

 

[hotrod180]

Can anyone confirm if the top male spade connector (circled red) is power?
I had some work done under panel and I think the spade connector for power came off. I want confirm that is the spot for a power wire before I plug it back in.
Couldn’t find it in maintenance manual....

The maintenance manual (for the early 180's anyways) has a LOT of wiring diagrams, including sub-diagrams for things like this.
You sure it's not in there?

 

[BC12D-4-85]

I briefly scanned through 2 C-185(*) SM's and didn't find a specific print. There is a basic wiring digram for an interior lights CB that feeds one of the gauges. Might not have found it tho. If that's the same board there's not many choices for wiring (the C669538-0101 model above). Others on e-Bay show posts for connections.

Gary

 

[hotrod180]

I think I would try hooking up the wires from the temp sensors to the SL & SR terminals, and see if the gauges worked.
Like someone posted on your FB thread, I think maybe those senders (probes) & gauges don't need power to work.
I'm thinking maybe the top connector is for connecting to the panel light circuit..

 

[BC12D-4-85]

The thermocouple non-electric fed sensors I've had use two wires per gauge. They complete a DC circuit that makes the gauge react. Typical for add-on CHT gauges that replace the spark plug gasket. If there's a single wire to the sensor, generally it's a variable resistance unit fed by buss DC through the gauge. But, not an A&P.

And not sure what the issue was here to begin with. Guess the gauges both stopped indicating? Any female spade ends for the gauges should still be nearby if tied down in the bundle.

Gary

 

[Cardiff Kook]

I plugged in the power. Dont think it resolved issue.

Would be interested to know if they dont require power.

Right now neither is registering anything

 

[BC12D-4-85]

Does the wire you believe to be the source of power show electrical buss voltage with the master switch on? As in does a voltage meter's probes placed between the wire end and ground show voltage? There's a resettable circuit breaker (via push - 5 amp?) that protects that wire and I believe interior lights. Make sure the wire's hot and the breaker not-tripped and also has battery voltage on both its terminals master on. Or, wires to the breaker can be removed and resistance across the terminals checked.

You could also heat the cylinder temp probe (hot air or?) to see if it activates the CHT gauge without battery power.

Edit: When powered with voltage that circuit board can supply both lighting and power to the gauges. Conductive electrical circuit traces and resistors determine who gets what voltage.

Gary

 

[Cardiff Kook]

The power line has power. They must have just broke something when they pulled the power line out.

 

[BC12D-4-85]

Gauge unit has to be grounded. Wires to sensors connected at both ends - to board and sensors. Have you run the engine to heat the sensors?

Gary