737-300 tq parking brake replacement

[kurt-olsson]

Hi.

I have tested the cables so they make contact. I noticed that the cables has been really worn and oxidated. But i cleaned and checked contace for the parking brake.

Shouldent the light turn on if i test with a 9v battery? I think the bulb might be broken...

Anyone know how to get the bulb out and which cables are - and +?
What does the middle cable do?

[727737Nut]

Bulbs are 28vdc,  Use a DVM to check for resistance on the bulb if you can't see the filament inside    There is no + or _ for light bulbs but the bulb housing could be the gnd which is sometimes the case in aircraft lighting.

[kurt-olsson]

Turned out that the bulb was busted. I broke the glass while trying to get the lamp out. I am starting to replace all the wires except the ones in the handle and toga buttons. I will replace it with a 12v lamp.
Question is where to find a lamp like that? Hm...

[FredK]

Search the web for "panel indicator lights".  I replaced the red lens and bulb with one that I sourced from Radio Shack here in the US.  Looks very much like the original.

Fred K

[mickc]

Kurt,

To answer your question, on that lamp in particular (as it is wired in the aircraft)

The middle terminal (1) is positive, terminal (2) is switched ground to activate the light, and terminal (3) is constant ground for the push to test function.
The terminal numbers are printed on the side of the lamp body.

Depending on what I/O cards you are using to control the light, you can switch the positive /negative side, as Rob said, the bulbs have no +/- side like an LED has.

If you only broke the actual bulb getting it out, these are easy to find, they are T3-1/4 Bulbs with a Ba9s base. 

These are bayonet bulbs, so you need to push them in slightly and turn 90 degree to remove them

[kurt-olsson]

Thank you for your answers, much appreciated.
With the new lamp it will be easier to test and hook up.

I have also removed the newly installed cables in the picture since i dont need them (as you said Fred).

Now i have removed the trim cutout panel snd will try to hook it up and replace cables.

[navymustang]

You may notice that the lens gets rather warm if left on for extended periods of time. I solved that by replacing the incandescent bulb with an LED bulb that uses the same base.  I can now leave parking brakes on for hours and no heat form the bulb at all on the lens.
Jim

[kurt-olsson]

Parking brake set!

Like you said, it does get hot.
Push to test works to.