Electical Question re: Pin 18 on Cab Relay

[jim_hoyland]

I just wired my Becker radio so the variable volume function would work. A wire was run from pin #1 at the radio to pin #18 of the dual relay for the cabriolet top. The mod has been well documented and I now have automatic increases in volume as the car goes faster.

My question is kinda techical: What is the signal pin #18 emits ? I want to install a CDR in my 914 and would like to figure a way to duplicate the signal. The first thought was to consider the Tach signal. Any eletrical geru's out there ?

Thanks,

Jim

[Burg Boxster]

I might be wrong, but pin #18 in the top relay does not emit any signal. Pin 18 in the relay is a cut off so that when it receives a signal it cuts power to the convertible top motors to prevent damage. Therefore, I would assume it gets the signal from the ECU for the speedometer. Wouldn't make sense for it to come from the Tachometer b/c you can rev the engine as much as you want when stationary and still raise/lower the top. Check the electrical diagrams in the back of a Bentley manual to verify.

Good luck

[jim_hoyland]

Good point, I had it backwards. My question should be what type of signal does pin 18 receive from ??????

My thought was to install a Becker in my 914; if I knew the type of signal controls the variable volume, I might be able to make a facsimilie ---with the help of someone with a lot more knowledge than myself.