|
Registered
Join Date: Apr 2010
Location: New Orleans, LA
Posts: 1,493
|
no, on the SC the speedometer sender sends its signal directly to the back of the speedometer. there is no relay that comes into the picture.
To the OP, where are you getting the "speed relay" designation? It could be part of the cruise (tempostat in German) system.
Quote:
Originally Posted by Dave Colangelo
I was actually looking over these schematics last night (for my 78SC which should be similar). If im not mistaken it works some thing like this. The speedometer sensor outputs a square wave, it is a toothed gear that is in the trans is run near an inductor. If the gear is magnetic, then a current will be induced in to the sensor. That sensor then outputs a square wave. I think the wave is used to trigger the relay. The reason they do this is that the output of the sensor its self can be some what unpredictable and not linear. The only thing that is constant is the pulse width of the signal. Thus by running it in to the relay, and making the relay trigger at a low threshold, a more linear and constant voltage can be controlled. So the output of the relay is a clean 12V P-P square wave with the same pulse width as the rough signal created by the sensor. Thus you should not remove the relay or try to bypass it in my opinion. It may also split the signal to go to the cruise control unit if you have one.
Regards
Dave
|
__________________
1982 911SC, Mocal oil cooler, Bilsteins, Carrera tensioners, backdated heat, factory short shift, Seine gate shift, turbo tie rods, pop off.
2005 Mercedes-Benz C230 kompressor sport 6-speed (daily driver)
|