URQ Brake lights

[Roy Wendell]

On Monday, July 23, 2007, at 06:10PM, Huw Powell <audi at humanspeakers.com> wrote:

>
>> I have been it seems driving for some time without brake lights.
>> Patient - 83 early under dash URQ
>> 
>> Fuse good.
>> Bulbs are good.
>> Grounds are good.
>> E-Flashers work.
>> Signals work
>> Pedal Switches work.
>> Rest of tailights work.
>> 
>> I have not had much time at all to look into this but last night I found I have no power at the pedal switches. I dread tracing this anywhere (if that is even possible) with the bundle of spaghetti wires the "superior German engineers" gave us to deal with.
>> Any usual suspects from BTDT?
>
>1. The pedal switches ground the circuit, IIRC.  No power there. 

snip

I disagree with the statement that no power should appear at the switch. With the switch open, the full voltage drop will appear across the terminals because it has infinite resistance. Regardless of where in the circuit from supply to ground the switch appears, with it open a meter will read full supply voltage across the terminals. With the switch closed it should read nearly zero. If this is not true then the next check is to see that one of the contacts reads battery voltage to ground and the other zero resistance to ground. This assumes that Huw is correct and the load (bulbs) are between the supply and the switch and not the more normal case where the load is between the switch and ground. In that case the resistance to ground for the non power contact would be some low resistance equal to the parallel sum of the bulb resistances.

Roy