Green gear indicator will not light, but press-to-test works

[cferr59]

I have a 1965 M20C with a johnson bar.   I had an issue today where my green gear indicator would not light.  However, the press to test feature works so I know the bulb is good.

To troubleshoot,  I retracted the gear, climbed to a safe altitude, put the gear back down and pressed the gear switch with my finger.  The red light extinguishes, but green light does not light.  I also confirmed the gear horn engaged when I reduced power to idle with the gear up.    I returned to the airport and was landed safely with the light out after giving the johnson many sharp tugs to confirm it was locked.

I looked at the wiring to the light and around the switch.  It all appears to be in good shape. 

Looking at the wiring diagram, it looks like the green light is wired to the NO side of the gear switch.  Unfortunately, I did not have a multimeter at the airport so further troubleshooting was not possible.  My plan is return tomorrow and check the switch.  I was wondering if anyone has ever had a similar issue and what the cause was.

Thanks

[Ruff Air]

The contact switch is a brass tab that extends into the down lock block. Mine had been bent slightly upwards so I jacked up the plane, swung the gear, gently bent it down a little... problem solved.


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[Prior owner]

Jumper from the red light terminal on the switch to the green light terminal on the switch to check the wiring from switch to green light. If it checks out, then it’s the switch. Clean the switch terminals While you’re there...

As mentioned above, the tang the Johnson bar pushes on could also be bent, or the switch mounting screws are loose.

Edited August 27, 2020 by PilotCoyote

[Ruff Air]

“To troubleshoot,  I retracted the gear, climbed to a safe altitude, put the gear back down and pressed the gear switch with my finger.  The red light extinguishes, but green light does not light. “


Oops. Different situation. Sorry.


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[cferr59]

Thanks, everyone.   I went to the airport this morning and confirmed that the switch is working using a multimeter.  I looked more closely at the light and determined the bulb/cover were slightly loose.  I pushed on it harder and also turned it a bit harder to the right.  That seemed to tighten it up and it works fine now.  

Curious, though, does anyone know how to remove the housing and bulb?  Does it just unscrew?  I was going to take it out to make sure the contacts were clean, but I ended up leaving it alone because I didn't want to break it.

[Ruff Air]

Mine will brighten or dim when rotated left or right. Don’t know how it comes off.


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[cferr59]

1 minute ago, Ruff Air said:

Mine will brighten or dim when rotated left or right. Don’t know how it comes off.


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Mine has that feature too.  In fact, I think dimming it in flight is what precipitated the issue.  I'm leaving it alone at this point since it is working, but was curious about how to remove it should there be an issue in the future.

[ArtVandelay]

Mine will brighten or dim when rotated left or right. Don’t know how it comes off.


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It unscrews, sometimes they can be harder to brighten so they unscrew instead. You can adjust brightness when you remove it, it just uses a shutter to dim the bulb.


Tom

[M20F]

5 hours ago, cferr59 said: I looked more closely at the light and determined the bulb/cover were slightly loose.  I pushed on it harder and also turned it a bit harder to the right.  That seemed to tighten it up and it works fine now.  

Late to the party but that would have been my suggestion.  Always start with simple and easy first.  

[carusoam]

The shutter is called an iris....it opens as it twists...

Cleaning and lubing always works...

It does push to test....

When unscrewed, the bulb falls out... 

If needed, these are standard aviation products and are easy to replace....

The switch it is connected to... in the down-lock block is supposed to be calibrated...

This way when the gear is down, but not locked... you don’t accidentally get a green light... followed by a surprise....GU style landing...

 

The reason for the calibration.... the block wears with flight hours... into an oval shape... if you don’t lock the gear all the way it will feel like it is up and locked, but not quite get there...

There is a test for that as well... it is called the thumb nail test...

 

PP thoughts only, not a mechanic...

Best regards.,

-a-