On Thu, Jun 21, 2012 at 4:18 PM, David Beierl <dbeierl@attglobal.net> wrote:

At 06:54 PM 6/21/2012, neil n wrote:
>
>> Sorry. Wiring in an LED is a bad idea.
>>
>> Shunting an LED directly into TVS circuit .....
>>
>
> TVS?  Anyway, a) a worn throttle body may very well have to be adjusted
> with the engine running; and b) a yellow LED and dropping resistor in
> parallel with the throttle switch is an entirely practical way to monitor
> the switch.  In practice you can run a single wire from the hot side of the
> switch and take your ground from up front.
>

Ok. I see that. Thanks for hint on resistor. (but why a yellow LED? <
kidding >)  But....

By "shunting", I meant connecting an LED in parallel at wires going to the
TVS (Throttle Valve Switch) plug. Maybe I'm still misunderstanding things.
Seems to me the ECU supplies both the -  and   +   to the throttle valve
switch plug.  (otherwise why can one measure voltage there, ignition on?)

Would shunting in an LED in parallel complete the circuit so ECU thinks the
throttle valve switch was closed 100% of the time?

You were a bit confused about what the ECU is doing.  The ground side of
> the switch is grounded.  The high side is supplied with five volts limited
> at some smallish current and the ECU watches the voltage on that pin.  High
> = open, low = closed.  It's threshold is set such that you can steal some
> for an LED without changing its operation.
>

Good to know about LED power draw. Much thanks.

Given the age of some parts on these Vanagons, rigging up a temporary
throttle valve switch light might be useful. As for setting the switch with
engine running, that might be an interesting thing to try though the
movement of the engine might make that tough. I had heard of Ken's O2
monitor. That is yet another thing I want to do on my new van!

Neil.

--
Neil n

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