Engine bay retractable light

[87MJTIM]

Does anyone know the name of or part number for the gravity activation switch in the light box?  I have a light that is in decent shape and want to get it working.  I can get continuity before the switch and after the switch.  The switch is supposed to make contact when the box is tilted up.

[eaglescout526]

Isnt that a mercury switch? I know Fords of the same era have the same kind of lamp assembly. Maybe GM ones have the same part as well?

[87MJTIM]

Mercury switch. That’s the name. 
 

Are there aftermarket options rather than searching through JYs?

[87MJTIM]

Found this:

 

 

[eaglescout526]

I have no idea on the aftermarket of those. I’d imagine it’s tough since mercury is toxic. 

[ghetdjc320]

Why not use an alarm tilt sensor? Very simple normally open contact that closes when tilted past a preset point. They are used in car alarms to deter theft by tow truck 

[Pete M]

lots of more modern cars have lights that turn on when the hood is popped.  how do they do it?

[garyweb3]

My 1980 Spirit AMX has a underhood light. I'll have to look at it and see if I can figure out what activates it.

[87MJTIM]

Update:

 

I re-examined the light again. The mercury switch didn’t look like it leaked. I couldn’t think of how it could go bad. 
 

I took sandpaper to the contact points and used pliers to bend the tabs. With the box held vertical, I have continuity on + and - wires!!

 

I then tested the cord wheel to the light socket. Again, I used light sandpaper and contact cleaner spray to the contact disks. I have continuity on both wires. 
 

I put the two halves together and tested continuity from the + feed to the light socket. With the unit held horizontal it was open circuit. With the unit held vertical it has continuity. 
 

The - has continuity full time. 
 

Mercury delivers. 

[eaglescout526]

Glad you got it working! Nice to know that is also serviceable. 

[pizzaman09]

Mercury switches are usually very reliable.  They are little more than a glass tube with a blob of mercury sliding around in it.  There are a set of wires that poke through the one end of the tube that the mercury makes contact with.  Just about every home thermostat built before the age of modern electronics has a mercury switch in it.  Particularly the ubiquitous round Honeywell thermostats put in every house from the 60s through the 80s.

[87MJTIM]

I did some searching and research on mercury switches and thought it just wouldn't stop working.  I decided to re-examine the unit and clean all the contact points.  I finally got continuity from the + wire in to the light socket with the unit held vertical.  I have not tested it to a battery yet.  The light bulb needs replacing.

 

Age and corrosion took its toll on the light .