Switch Will Not Stay On

[AH-1 Cobra Pilot]

Lately, my landing light switch will not stay in the ON position.  It seems to stay ON for my initial taxi, but once the engine RPM comes up, it turns off.  (Vibration?  Electrical load?)  I can hold it ON, but it will not stay ON.  Is there a way to fix it, or must I replace it?

[tmo]

Is your light LED or traditional?  It will draw different amounts of current, which might influence the trip (assuming the switch is a circuit breaker as well and it just trips).

[takair]

1 hour ago, Ah-1 Cobra Pilot said:

Lately, my landing light switch will not stay in the ON position.  It seems to stay ON for my initial taxi, but once the engine RPM comes up, it turns off.  (Vibration?  Electrical load?)  I can hold it ON, but it will not stay ON.  Is there a way to fix it, or must I replace it?

You likely have a circuit breaker switch that degraded over time. If you reach behind the panel, it is likely quite warm before it trips. They are unfortunately quite expensive. Sometimes you get lucky with a salvage one. I have also had some luck soaking it in electrical contact cleaner and exercising it (power off!!).  Oh, be sure you don’t have a real short circuit downstream first. 

[Hank]

Mine did this once. Insulation on the wire rubbed through on the inside of the lower cowl. Fixed that and it stayed on  

Now I've gone LED, and current draw is way down. 

[carusoam]

+1 on the CB switch wear... who would know a CB would suffer from mechanical wear..?

My M20C landing light kept turning off on me...

It also got bumped by the floppy instrument panel that was lacking the proper support hardware...

New CB/switch and rubber hardware from AS fixed the problem...

Best regards,

-a-

[chriscalandro]

Likely just the switch. It takes 10 minutes to swap. Don’t get a salvage switch, get a new one. 

[larryb]

Either the circuit breaker switch is faulty or the switch is properly doing its job protecting you from a short due to a chafed wire.

[RobertGary1]

Unfortunately these are not cheap CB switches. Will set you back some bucks.

 

-Robert

[GeeBee]

A C/B protects your airplane from an electrical fire. You should not reset a C/B more than once and even then only if it is an urgent need. After one reset and trip leave it alone until the circuit is repaired. Never reset a fuel system C/B trip. Most airlines do not allow their crews to reset C/Bs unless a greater emergency exists. In fact many newer designs, the C/B are not available for crew access. You should not be constantly resetting this circuit, until the cause is investigated and repaired.

 

[Yetti]

Take your phone and take pictures back there.   Might be a panel sag or some other random screw.

[cferr59]

14 hours ago, RobertGary1 said:

Unfortunately these are not cheap CB switches. Will set you back some bucks.

 

-Robert

Yup, I just had to replace my pitot heat breaker/switch.  $200 dollar switch! 

[Yetti]

In the earlier models the light ran off the switch.   in my 75  F I believe there is a relay that the switch runs, but the heavy load goes through the relay.  with a J I believe there is a relay for the landing light.

[Steve W]

All J's whose wiring diagrams I can read also use the switch. The only difference is early models it's a switch-breaker at 20 or 25A. Later models with wing lights use 2 breakers in the main breaker panel one for landing and one for taxi and a pair of split(not-breaker)switches so you can use left or right sides alone.

 

[FloridaMan]

It’s probably cheaper to replace the light with an LED than the degraded switch. If it’s got PAR36 lights, go with the Teledyne Alphabeam

[AH-1 Cobra Pilot]

Even with all electrical power off, the switch would not stay ON.  I removed the switch cover to find the spring misapplied and the hinge pin on the other side missing, putting more tension on the spring.  I replaced the pin and reset the spring, and all is now fine.

I suspect the pin worked its way out gradually, causing the rest of the malfunction.

[bradp]

My general buckets for a CB tripping repeatedly have been - 1) motor failure / motor strain 2) short circuit, 3) spring on CB worn. 

[carusoam]

Interesting follow-up Ah-1!

think it will stay together?

Best regards,

-a-