Landing Light Switch

[Sven]

On a night flight this evening my landing light switch kept flipping off on its own. It's a brand new replacement switch from Spruce. It happened four times tonight. Is my Mooney haunted?

[MooneyMitch]

Hey Sven.

It appears not to be your switch.  Circuit overload, it sounds like to me.  Very possible it's old wiring, maybe frayed a bit and touching something else, or just not able to handle the load any longer.  My 2 cents only.

[Sven]

I didn't know a switch could turn off by itself. It moves from the up to the down position. It does that (without being haunted)? When I first turned it on tonight I did hear a crackle in the radio. I didn't like that.

[Lood]

Many of the toggle switches doubles as a circuit breaker as well. So, if it "switches itself off" is basically tripped, which indicates some or other problem. I'd have it checked.

[piperpainter]

I've had this happen as well. Thats why you'll see the little numbers on the switch. Thats the AMPS for the switch/breaker that it is!

[carusoam]

Make sure the "new" breaker/switch matches the proper load.  20 amp breaker is typical for this application.  Check to make sure you have the right one.  The headlight circuit is pretty short, the old wire is rigid and contacts the vibrating cowl in many places. The old insulation is easy to fray.  Also check the "blade" style connectors to make sure that they are insulated.

-a-

 

[Sven]

I did get a 20 amp switch. I'll have to hunt down the short. Hopefully this will be an easy job (I'm laughing on the inside).

[carusoam]

If the wires are in their original condition.  The wire runs along the copilot side of the cowl.  I believe it is a single wire 12V+  the bulb has two wires out of it.  One grounds near the bulb to a screw at or near the cowl.  Near the bulb is an old style blade connector.  the connector is an old version of quick disconnect.

Bring your ohm meter or simple continuity tester with you.

If it is shorted, it should be fairly easy to identify.  It is probably soaked in 40+years of oil and dirt too.

Your A&P can help you "modernize" the wire in a very short period of time.

-a-

[danb35]

I'd even think that modernizing the wire (and any related work) could be legal owner maintenance--you're specifically given the ability to repair landing light wiring circuits (wonder why only those).

[Immelman]

[Hank]

Quote: Sven

I didn't know a switch could turn off by itself. It moves from the up to the down position. It does that (without being haunted)?

[Sven]

We found the culprit tonight. The positive lead coming off the lamp is long to allow for an easy on-field change. That extra length happened to be touching the exhaust pipe and the insulation was burned through. Funny this was never caught before. Our hangar neighbor is an A&P and he immediately hooked us up with the right wire and connectors. We ran out of light tonight so we'll put her back tomorrow.

[danb35]

...and a week or so after my initial post in this thread, I had a problem of my own--turned the switch on, heard a faint crackling in the headset, and it turned itself off.  Spent some time on Friday running a new wire from the switch to the landing light--just finishing up the logbook entry now.  Glad it wasn't the breaker/switch--best price I could find on those was around $150!

[danb35]

Well, I may have spoken too soon about my issue.  A couple of weeks ago, as I mentioned above, I had the switch turn itself off in flight.  Resetting it, it turned off again after a couple of seconds.  I couldn't inspect the entire length of the wire, so I just ran a new wire from the switch to the light, and it worked fine on the ground.

Yesterday, I went to go fly, and the light again worked fine on the ground.  But as soon as I applied takeoff power, the switch popped off again.  After landing, again, it works fine on the ground, but not when takeoff (or even cruise) power is applied.

My current working hypothesis is that the increased vibration is causing the (presumably work--it's got over 40 years and 6000 hours on it) switch to turn off, which would require replacing it.  Is there something else I should check first?

[carusoam]

Don't hesitate on changing out the landing light switch/CB.  They don't age well....compared to the rest of the plane, anyway.  It is not too difficult to swap out.

LL Circuit: buss, Switch/CB, wire, blade style disconnect, bulb filament, ground...  It doesn't get much simpler than that.  If the wire and disconnect are insulated properly, the only thing left is the CB.  They are heat triggered based on current running through it.

I think it is possible that the vibrating instrument panel is easier to trip the CB, when it is at it's limit, than sitting still.

Best regards,

-a-