Query about position of fuse and diode- boost controller

[mattxorph]

Hi All,
I am putting together an MS2 V3.0 and putting in the additional components for the Boost controller.
http://www.msextra.com/doc/ms2extra/MS2 ... .htm#boost
I am curious why the fuse should be positioned after the solenoid and not between the +12V ignition and the solenoid. Surely this leaves unfused 12V wiring going into the engine bay to the solenoid. What am I missing? Does the fuse protect the megasquirt circuitry possibly?
Also, regarding the diode positioning, if this was wired to the internal 12V power to the Megasquirt as shown, it could potentially allow backfeed through the solenoid if the 3A fuse for the MS was to blow for example.

Cheers,
Matt

[SymTech Laboratories]

I am curious why the fuse should be positioned after the solenoid and not between the +12V ignition and the solenoid. Surely this leaves unfused 12V wiring going into the engine bay to the solenoid. What am I missing? Does the fuse protect the megasquirt circuitry possibly?

You could install the diode at the solenoid connector if you want; this theoretically does a better job of suppressing back EMF, but we prefer to install it inside the MegaSquirt enclosure.

Also, regarding the diode positioning, if this was wired to the internal 12V power to the Megasquirt as shown, it could potentially allow backfeed through the solenoid if the 3A fuse for the MS was to blow for example.

That's true, but the solenoid should be powered by a relay that the MegaSquirt ECU controls (e.g. an ASD or "main" relay).