Volvo Penta MD22 Wiring - Earth Relay?

[nigelmercier]

I've re-drawn the Engine and Instrument Panel wiring diagrams for my Volvo Penta MD22, see here.

I'm still confused over one aspect, the Ground Relay. With the Instrument panel diodes installed, this relay seems to fire when either the Start or Stop function is activated, putting a ground onto terminal 31 on the Starter Motor, which is already at ground potential.

Any ideas why?

[exfinnsailor]

Total Rubbish Deleted ..

Start again .. Pin 8 drives the relay so when ever the key is in position S or 19 the relay will be on .. So if you take the diodes out it will not work .. Its not connected to anything anyway ..

[skipper_stu]

On mine there is a ground relay, it is to activate the electric windlass, it is a piss poor installation, done by the original dealer i think, i took it out of the equation, the windlass stopped working!
I think it is to prevent the windlass being used when the engine isnt charging
Stu

[Hoolie]

I have a similar arrangement on my Perkins Prima M50 (same engine). The engine is therefore normally isolated from battery negative and is not earthed. I have always assumed it avoids the need for anodes in the cooling system and reduces other possible sources of corrosion.
It's a nuisance though as isolated starter and alternator are much more expensive [img]/forums/images/graemlins/frown.gif[/img]

[nigelmercier]

[ QUOTE ]
The engine is therefore normally isolated from battery negative and is not earthed. I have always assumed it avoids the need for anodes in the cooling system and reduces other possible sources of corrosion.
It's a nuisance though as isolated starter and alternator are much more expensive [img]/forums/images/graemlins/frown.gif[/img]

[/ QUOTE ]

Ah, that makes sense. The switched ground tag has been removed on my boat, and the engine is indeed grounded.

Bond everything, it's the only way! [Expecting many, many replies saying the opposite] [img]/forums/images/graemlins/smile.gif[/img]