[Top] [All Lists]

Re: Hot Light Switch

To: mgs@Autox.Team.Net
Subject: Re: Hot Light Switch
From: (Robert J. Donahue)
Date: Tue, 1 Jul 1997 01:18:46 -0600 (MDT)
>Mark Moburg wrote:
>> In any event, when you run any current through a
>> wire, it will heat up.  How much it heats up is a factor of how much current
>> you put through it.  Your lighting switch carries all the current for the
>> head lights, front marker lights, side lights (if you have them), tail
>> lights, licence plate lights and dash lights.  No wonder the poor thing is
>> sweating.
>  Sure. Just to extend this, the heat is caused by current through
>a resistance.
>  Every wire, every join, and every connection is a resistance,
>and could develop some heat. I know that the contacts in the
>switch are probably a fairly high resistance, so some heat is
>to be expected.
>  I guess my roundabout question is really asking if my switch
>is making a poorer connection than it should, leaving a larger
>resistance and a greater source of heat.
>Trevor Boicey
>Ottawa, Canada

I noticed that the light switch on my TD runs warm. A little investigation
revealed that the hot part was a flat metal strip on the back. I believe
this to be a fusable link and the heat is probably normal. Off hand I would
say that a plain switch should not have enough resistance to run "hot" but a 
has a deliberate amount of resistance and will be quite warm when running 
near it's rated current. Even though there is no distinct fuse in the headlight
circuit, I bet something was designed to give in case of a hard short. 

Something you could do is measure the voltage across the switch. If it is
something over about a half a volt, it has too much resistance even if it
has a built in fuse. (I'm just guessing at this half a volt, has anybody
measured this on a known good switch?)

Bob Donahue, Still Stuck in the '50s           
53 MG-TD #17639 under DIY restoration, NEMGTR #11470
71 MGB still in shop, 17 months and counting

<Prev in Thread] Current Thread [Next in Thread>