Landing light switch CB popped

[anthonydesmet]

Gents,

just went out for a short spin, the first in a couple weeks. Twice around the pattern at pattern power my landing light switch cb popped and also I could smell a slight electrical smell.  Light and switch work fine during pre-flight on ground without popping.  M20K. 263, 1980.  I believe I have klixon switches also.  I went behind panel to look for anything obvious but all looks ok. I traced the wires out best I could to look for any dark burnt spots or any possible crossed wires.  Could it just be the switch.  I would think the switch is working the way it is supposed to. Thoughts?

[ArtVandelay]

Wire could be frayed and shorting out on metal, do you have wing mounted lights?

Occasional faults are frustrating to track down, good luck!

[N201MKTurbo]

That is a common problem. The 250 W landing light runs pretty close to the current limit of the circuit breaker. The breaker gets old and tired and trips. An LED landing light is probably the best option.

[carusoam]

How was the temperature in the cabin today?

I used to use my landing light in my C as a recog light.  The CB got old and began failing.  They are temperature sensitive.

If it is original, it would be good to swap out.  They wear with time and use.

The other thing that does it...  The old vibration adsorbing mounts of the instrument panel above the CBs wear and get loose.  The panel droops into the CBs.  Thence turning off the weakest ones which are about to trip.

These are probably just old C issues.  Easily fixable sort of...

Best regards,

-a-

[anthonydesmet]

Gents,

Sorry, here is some more info.  On the K model there are 2 x 100-watt landing lights right next to each other on the nose under the propeller.  I was brain storming with my mechanic before I went home and we got to thinking....we have taken the cowl on and off quite a few times in the last month with oil change, troubleshooting a couple issues and maybe think we have scraped a wire somewhere....maybe as it goes into the firewall.  If it were in the engine compartment I don't think I would have smelt the electric fume when the CB popped, although I did have cabin heat on in the descent so I guess it might have came through then.  The smell was pretty instantaneous and then gone.

[N601RX]

A short will trip the breaker almost immediately.  If it's taking a couple of minutes to trip then it's likely either a weak breaker or lose screw/corrosion between the breaker and buss bar.  The smell was probably the breaker getting hot.

[WilliamR]

I've had something similar happen a few times on a 252, which, if memory serves, has a similar setup to the 262 firewall forward.  There is a large (3" diameter maybe) scat tube that runs across the front of the engine just below the exhaust and expansion joint heat shied.  I can;t remember what that scat tube is for; possibly heat from the pilto side shroud to the passenger side shroud.  Check that scat tube for wear and exposed wire.  I have found that scat tube will rub against the light contact posts over time to the point the wire from the tube is exposed and will cause a short.  A little RTV behind the light posts goes a long way to prevent this in the future.

Hope that helps.

William