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Re: [T3] Flasher unit

On 12 Nov 2003 at 8:19, Daniel Baum wrote:

> Perhaps we're looking at it the wrong way; maybe originally the red light in
> the switch was supposed to be the only interior indication that the
> emergency flashers were working, but they couldn't stop the dashlights
> flashing when the ignition was ON, because they needed this for the
> indicators and it's all based around the same circuit. So later they kludged
> it a bit more so that the dashlights flashed whether the ignition was on or
> off!

All the dash indicator lights generally have 12V applied to one side of them 
when you turn the key ON, and then they light whenever there is a good ground 
provided on the other side. I think that the 68-70 flasher just provides an 
intermittent ground for those lamps. So when you turn the ignition OFF there is 
no longer any 12V supplied to those bulbs and the intermittent ground is still 
provided, but it doesn't do anything.  

In the later system, the relay provides an intermittent 12V (rather than an 
intermittent ground) to both the dash lights and the external bulbs, all wired 
in parallel, so, with the ignition on, when that flasher 12V is on, the dash 
lights are off (they're getting 12V from both sides) and when the flasher 12V 
is off, the dash lights are on (because the flasher side is grounded back thru 
the external filaments.  

Thus, on the late systems (71-3) I think you will find that the phase of the 
dash bulbs changes when you turn the key ON.  

Another thing I think you'll find on the late systems, but I've never tried it, 
is that the dash lights won't flash with the key ON if you remove all the 
external bulbs, since those provide the ground path for the internal bulbs  

Jim Adney
Madison, WI 53711-3054

List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org

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