Landing Light

M

meritflyer

Well-Known Member
In a Mooney M20K -

When I flip my landing light on, I get a massive discharge on my ammeter, a low volts annunciator, and the rocker switch kicks from the ON position to the OFF position. It only happens when the engine is running.

Any thoughts?
 
Intermittent short in the landing light circuit is the best I can come up with.
 
Sounds like the switch is the CB (haven't seen that on any of the pistons I flew, but that isn't a lot). If it is tripping only when the alternator is running something is exceeded the amp rating for the switch/cb.

Remember, the CB is there to protect the wire, not the device. Something needs to be replaced. I wouldn't fudge with it anymore until you get a mechanic to check it out and find the problem.
 
Definitely don't mess with it. I remember making an emergency landing, at night, at an unfamiliar uncontrolled field in the middle of nowhere, alone, sans landing light because of something very similar.
 
Thanks for all the responses.

The previous owner said he had something similar about a year ago so they replaced all the wiring and switch which did the trick - until now.
 
Could be a switch or a ground issue.

Landing lights are wattage intensive, is it possible the alternator 6 way diode bridge has some failures and you aren't putting out enough charge from the alternator? Leave the landing light off and turn on everything else and transmit both radios if you can, maybe you can recreate that current load. That might explain why it only happens with the engine running.
 
UPDATE for those wondering...

The terminals in the landing light had chaffed through some scat tubing which was shorting out the wire wrap. Pretty easy repair.

She's back in business!
 
meritflyer said:
In a Mooney M20K -

When I flip my landing light on, I get a massive discharge on my ammeter, a low volts annunciator, and the rocker switch kicks from the ON position to the OFF position. It only happens when the engine is running.

Any thoughts?
Click to expand...

I had a similar problem, weird. Found out it was short and grounding some where else.
 
400A said:
Sounds like the switch is the CB (haven't seen that on any of the pistons I flew, but that isn't a lot). If it is tripping only when the alternator is running something is exceeded the amp rating for the switch/cb.

Remember, the CB is there to protect the wire, not the device. Something needs to be replaced. I wouldn't fudge with it anymore until you get a mechanic to check it out and find the problem.
Click to expand...

@ 400A, Best avatar picture ever.
 
You must log in or register to reply here.
Back
Top