"W" signal on Volvo B20 AQ130D

[GlastronV174]

Hello,

I've been looking all over the web for a solution but can't find it.
My 1973 Glastron V174 with Volvo Penta AQ130D has an alternator without a "W" connection.
I need this connection to feed to my new digital Wema Tachometer. The previous boat owner thinks
the signal comes from the coil, but at wich connection should I put the wire for the tach?

Many thanks!

 

[Don S]

Re: "W" signal on Volvo B20 AQ130D

Gas engines use the - terminal of the coil to signal the tach, not the alternator.

 

[GlastronV174]

Re: "W" signal on Volvo B20 AQ130D

Gas engines use the - terminal of the coil to signal the tach, not the alternator.

Thank you Don. So connecting a wire from the - terminal on the coil will do the trick?
What ratio do you think the signal will be? As in; how many sparks/signals will be one revolution of the engine?

Thanks!

 

[Don S]

Re: "W" signal on Volvo B20 AQ130D

IO engines have used this method for ever. The tachs are usually set to the number of cylinder. You may have the wrong kind of tach.