Charles22

Strange Relay/Diode Issue

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Good evening, 

Has anyone ever seen this, on an F model Mooney. I have been having an issue with my battery master switch not turning off after flight or turning itself on when the plane is in the hangar. 
 

After a new switch, two new master solenoids. A not so great mechanic, I finally came across this culprit with an A&P friend. A relay that is nowhere on my electrical diagram and is connected to the battery and the switch and seems to be acting like a relay in line with the battery master relay. On the diagram there is one wire running from the switch to battery master relay but in my mooney it appears this wire runs to this relay first. And then to the switch. 
 

Everyone is saying a bad ground or a loose wire but this relay may very well be the issue. any help is greatly appreciated as I don’t think this is standard. 
 

for reference we found this relay by the circuit breakers on the pilot side. The plane has some avionics upgrades, EDM830, Aspens, etc... 

91562D95-3AC8-4D3E-BB34-2FEFAF6DEA14.png

20DDEE45-DF6C-4BFF-8B57-A1392EA1D8BE.png

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I have seen something like that under the hood of my Chevy Tahoe...


First thing to do...

Grab a copy of your POH to see if the electrical diagram has a relay in it wired the way you have it in your hand...

The picture on the device looks like a relay that opens and closes four separate switches...

To learn more about that device, a web search of the part number and manufacturer will supply the answers...

If it is the right part, it is failing to stay shut off when it is supposed to...

Cleaning it might work, replacing it would be easy...

Subtle hint... if it doesn’t cost hundreds of dollars to replace, it is probably the wrong one...

 

Realistically, work with your good mechanic, get the wiring diagram he needs, and pull out the things that don’t match the wiring diagram...

With all the proper parts you have replaced, this thing is probably just going to be pulled out... and the wires routed properly...

If you can’t get enough detail from your POH wiring diagram... the MM is the right place to go...

Mooneys typically have a bunch of relays for various jobs... Master relays and instrument panel relays are silver can shaped devices usually close to the battery..(?)

PP thoughts only, not a mechanic...

Best regards,

-a-

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I had an 84 in the past and a 97 now. So never a 75. That said, your relay does not look like a factory install to me. The factory would not need to write those notes on the side and it would be mounted better. So somebody in the past made a mod. It certainly could be your problem. It will take a person very comfortable with electronics to either fix it or return it to factory spec. I may be wrong, just my guess from the pics and my own experience.

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To figure this out, I would recommend tracing the wiring and draw a schematic so that you can analyze it and use it to show us so we can help figure it out.

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The can be two relays up there.  One is the landing light.   The other is Comm buss master.  Potter Brumsfield is the standard mooney install so that is the key.    The comm master is a normally closed relay.   So when you turn the master on, through the com switch power is applied opening the com relay you are holding.   When you turn the com switch off power is removed the relay closes again.  and the radios turn on.   There is also a wire from the starter relay that will supply power to the relay so your radios go off when the starter is cranking.  The wire has a diode to keep current from flowing back to the starter relay.

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the com relay controls the 2 bottom rows of breakers in your 75 F.

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Good evening, 
Has anyone ever seen this, on an F model Mooney. I have been having an issue with my battery master switch not turning off after flight or turning itself on when the plane is in the hangar. 
 
After a new switch, two new master solenoids. A not so great mechanic, I finally came across this culprit with an A&P friend. A relay that is nowhere on my electrical diagram and is connected to the battery and the switch and seems to be acting like a relay in line with the battery master relay. On the diagram there is one wire running from the switch to battery master relay but in my mooney it appears this wire runs to this relay first. And then to the switch. 
 
Everyone is saying a bad ground or a loose wire but this relay may very well be the issue. any help is greatly appreciated as I don’t think this is standard. 
 
for reference we found this relay by the circuit breakers on the pilot side. The plane has some avionics upgrades, EDM830, Aspens, etc... 
91562D95-3AC8-4D3E-BB34-2FEFAF6DEA14.thumb.png.c5bbc45553cc74314e8c6c37a3d6a739.png
20DDEE45-DF6C-4BFF-8B57-A1392EA1D8BE.thumb.png.a7276977187e67c5b9df4949dce4cd36.png


My 1975 F does not have a relay like this. Nor did my F have an avionics master. Looking at the way it was installed and the location, my guess is that it is a relay for an avionics master. Do you have an avionics master?

I would track the wires and see where they go.


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Tracking wires is easier said than done, since they are all the same color, and once they come to one of the connectors...forget it. If you’re lucky you can read the id code off the wire if factory installed, you’ll need a magnifying glass.

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Mine did not have a relay installed either.   See pic below.    Some had removed it.   The problem is that with the old KX170s and the current draw,  I believe the relay was undersized

How someone fixed mine.   And yes the electrical tape was falling off and exposing a really big wire to direct short.

IMG_20180217_082130.thumb.jpg.481f1929e1a4b1b9eac80a7141936fa6.jpg

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You mentioned it goes to the battery and the switch....do you mean the master switch?  Some thoughts.  Do you have a mystery switch in the panel?  Some aircraft...mainly jets...have a ground clearance switch that turns on just a radio to allow getting. A clearance on ground without turning on all the usual loads.  Another thought, do you have a clock or radio that requires memory when master is off?  Kind of a cumbersome way to do it, but some folks like complexity.  Could also be some clunky Hobbs meter circuit or a theft prevention thing.

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Do you have an avionics master switch or just the battery master? 

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You mentioned it goes to the battery and the switch....do you mean the master switch?  Some thoughts.  Do you have a mystery switch in the panel?  Some aircraft...mainly jets...have a ground clearance switch that turns on just a radio to allow getting. A clearance on ground without turning on all the usual loads.  Another thought, do you have a clock or radio that requires memory when master is off?  Kind of a cumbersome way to do it, but some folks like complexity.  Could also be some clunky Hobbs meter circuit or a theft prevention thing.


My 75F had just a master switch and no avionics master. If Yetti is correct, there was a radio master circuit breaker (this may have been a physical switch)

bdde6084c8e5f01bc7ac623bed6ccf7e.png

And the relay is depicted in the schematic.

b8a2a6b4015bf5451a4f8f29cd764a31.png

What I found on my plane was that every radio had been wired to the master switch and I had to turn them all on and off before I started the plane. My first order of business was to have an avionics master installed with the appropriate relay.

d6d1bab47bbfb1435bbb7065643ad360.jpg


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