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Re: [Shop-talk] looking for small light bulbs

To: Steven Trovato <>
Subject: Re: [Shop-talk] looking for small light bulbs
From: Pat Horne <>
Date: Mon, 25 Feb 2008 15:56:40 -0600

Cold resistance of a bulb is much lower than hot resistance. That's why 
most bulbs burn out when you turn them on.

While it may not have an exact correlation, I just measured the cold 
resistance of a 130V 75W bulb and it measured 21 ohms. That would be 804 
Watts cold filament dissipation. Using Ohms law, the resistance of a 
130V 75W lamp will be 225 ohms hot, so you might be able to measure the 
resistance of another lamp and multiply the resistance by 10 to get hot 
resistance, but my measurements is just a sample of one. YMMV.


Thusly spake Steven Trovato:
> Are there other switches in the same panel that are lit to the same 
> brightness?  If you are so inclined, you could always measure the 
> resistance of a working bulb in another switch and derive from 
> there.  V=IR and all that rot.
> -Steve
> At 10:37 AM 2/25/2008, Pat Horne wrote:
>> Are there any Pick-A-Part places where you could pull another switch for
>> cheap? Or is there a group for these cars where someone could give you
>> the current draw for the lamp?
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Pat Horne, Owner, Horne Systems 
(512) 797-7501 Voice            5026 FM 2001  Lockhart, TX 78644-4443
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