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Mercury switch/Hobbs hood lamp
#1336737 Sat Dec 07 2019 02:09 AM
Joined: Aug 2017
Posts: 437
S
Shop Shark
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

Attached Files
20191205_170500.jpg (145.05 KB, 284 downloads)
20191205_153354.jpg (401.49 KB, 284 downloads)
20191206_171200.jpg (225.12 KB, 265 downloads)
Last edited by Shaffer's1950; Sat Dec 07 2019 02:18 AM.
Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336743 Sat Dec 07 2019 02:52 AM
Joined: Mar 2019
Posts: 851
G
Shop Shark
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

Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336748 Sat Dec 07 2019 04:20 AM
Joined: May 2005
Posts: 7,272
B
General Purpose
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. blush
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.


I'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336773 Sat Dec 07 2019 02:04 PM
Joined: Aug 2017
Posts: 437
S
Shop Shark
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.

thumbs_up

Last edited by Shaffer's1950; Sat Dec 07 2019 02:06 PM.
Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336813 Sat Dec 07 2019 07:38 PM
Joined: May 2005
Posts: 1,636
B
Shop Shark
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.


Six volt guy living in a twelve volt world
Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336941 Sun Dec 08 2019 06:42 PM
Joined: Dec 2003
Posts: 3,953
S
Shop Shark
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.


"Sedgewick"
1949 Chevy 1/2-Ton
1989 Caprice

Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336966 Sun Dec 08 2019 09:12 PM
Joined: May 2005
Posts: 7,272
B
General Purpose
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'm away on an ego trip. Will be back on Feb 30.
I'm not an Auto Mechanic, but I play one on TV.
I charge $0.02 for every opinion and I take Paypal.
Plan B is always better than plan A, by definition.


Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1336998 Mon Dec 09 2019 12:41 AM
Joined: Aug 2017
Posts: 437
S
Shop Shark
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

Attached Files
20191208_163348.jpg (178.7 KB, 125 downloads)
Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1337085 Mon Dec 09 2019 07:27 PM
Joined: Dec 2003
Posts: 3,953
S
Shop Shark
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.


"Sedgewick"
1949 Chevy 1/2-Ton
1989 Caprice

Re: Mercury switch/Hobbs hood lamp
Shaffer's1950 #1337108 Mon Dec 09 2019 10:47 PM
Joined: Apr 2008
Posts: 785
F
Shop Shark
How do you remove the mercury switch on the Hobbs light? I can see how and I don't want to destroy the light.


Ed
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