The Stovebolt Site Forums The Shop Area The Electrical Bay Mercury switch/Hobbs hood lamp

I just got a hold of a John W Hobbs underhood lamp.
When I tested it , it worked but at a very high angle (held it with my hand) once I mounted it, it will not turn on. (Lower angle? )
Do the Mercury switches go "bad" ?
Can I get a replacement one? (When I searched, I did not find anything close to the one I need)
Any information would be great.
It looks great but if I can have it working correctly I'll try .
Thank you.
Todd

Another option would be wire it, "on and off" I'd always think in the back of my over thinking head that the mercury switch would fail in the on direction and battery/starter issues would result. A toggle switch might do you a favor in the long run. But I do understand the purpose and function of the product. JMO

Assuming you are saying the light works. Assuming the mercury switch works. Assume the switch is in the bulb socket area and not on the firewall.. Therefore place lamp on the inside of the hood, as you did, and tilt it until it goes on. That there would be the angle it wants. So bend, beg, borrow or steal a way to mount it at that angle. Pretty simple.
What is that cylindrical black object wired into the pigtail wire that is seen on the firewall? I do hope that is not the mercury switch.
Yes new mercury switches are available. Not exact. This is a glass encased one, there are also potted types.
Assuming "high angle" means if the hood opened farther, it would light.

Baramos,
Yes the light works.
The Mercury switch only works when it's almost straight up and down. ( no way to bend it to that angle , hood would have to be straight up.)
I tried bending it once mounted on hood but you only have maybe one inch to work with.
The cylindrical object is the in line fuse (I think original to the Hobbs light).
The Mercury switch sits below the light bulb at the socket.
Seems like it's the mercury switch.

My experience with mercury switches, which were high current units, is they always fail in the off condition. This is due to oxidation of the contact posts inside the bulb.
Orientation of the switch is everything.

I have a similar problem with my under hood lamp. The mercury switch is like the one pictured in your post. However when the hood is up the light is off, down and the light is on. I thought maybe the mercury switch was inserted upside down. So I changed it and put the tit on the switch down and the rounded end up. Now the light works all the time regardless of the position.
I didn't plan on making it operational but after seeing how neat it looks I want to. I do not want a toggle switch however.
I am not concerned about draining the battery as I have a master cut-off switch and anytime the truck is parked/stored the switch is off.

A cut off switch is a good idea.
Switches are available as evidenced by my hypertext link above. None of this is rocket science. Light is on while working in daylight or garage for hours.

I tried reversing the mercury switch. It did come on briefly but would not stay on.
I like the In-Line switch idea maybe at fuse?.
For now I replaced the mercury switch with a same size piece of steel. Works perfect. So it's the mercury switch.
Thank you all for input.
Todd

Took the unit to the local auto electric shop. They could not find the problem and auto electric is all they do. Tried reversing the mercury ball and putting the pip facing up and the light worked in reverse as I mentioned above. Put the ball face down with the rounded end up and the light was on constantly regardless of position.

How do you remove the mercury switch on the Hobbs light? I can see how and I don't want to destroy the light.

Forty9,
Remove bulb.
Just below bulb is the mercury switch.
Use a magnet if it's mounted on hood. Or turn it upside down, it should just fall into your hand. See my first post picture of my hand. That is the mercury switch.
Todd

Exactly. Don't think my unit is a Hobbs as it doesn't have an in line fuse. My mercury switch is rounded on one end, with a pip or nipple on the other. If anybody can find a source for these let us know.

Unfortunately there is a non-metallic/fiber washer at the base of my light socket with a hole for the bulb positive contact to go through. I hesitate to pry this washer out as it's very tight and I don't want to break it. It is a Hobbs light but someone may have modified it. I can get it to work if I tap on the bulb or housing. Maybe just one of those things. Thanks for the help.

Got mine working last Sunday. Pointing up - works. Horizontal its off.

Went for dinner, came back and its not working. Must be those gremlins I see occasionally around my shop.

I wonder if anyone has a lamp that consistently works the way we expect it to without tapping it or doing something else to get it to work. Maybe we're just chasing our tails.

Get modern will ya.

I do have a 1940's " Homart Fisheye" flashlight that Works too !

There ya go! Now you can see your motor at night.

So it would seem that there are not any Hobbs mercury switch under hood lamps that work consistently.

Took mine to a long time electronics repair shop. Does radios, TVs with tubes and all sorts of home electronics. He checked the mercury switch and it works perfectly. As it was Christmas week he closed but told me he could fix it. We'll see next week. If anybody can he can.
For those of you with a switch, remove the bulb and look into the socket and tell me if you see one of those brown plastic-type discs sitting on top of the mercury switch. I am sure mine had one but somehow it got out and lost and am wondering if it was meant to insulate the mercury switch body from the bulb.

Keep us posted on your results. Thanks. Ed

I will re check mine. I do not believe there is a disk between the contact and mercury switch.
Todd
Forty9, can you post a picture of the disk? ///

I do have a disc (Bakelite?) in my socket with a hole in center for positive contact.