I'll need to track that wire and see where it comes from...since I have an
early '89, it could come from either relay.  I've checked the voltage at
the ISV connector with the ignition on  but not running and got 5V...which
suggests that the ISCU is getting power from the ECU power relay and not
the fuel pump relay....I think

Patrick Spragge

From:   vw_van_fan_Mark <madvws@COX.NET>
To:     vanagon@GERRY.VANAGON.COM
Date:   10/01/2015 11:37 AM
Subject:        Re: Idle Stabilizer Valve part numbering question
Sent by:        Vanagon Mailing List <vanagon@gerry.vanagon.com>

Yes, at some point during 88 the FI wiring changed so that the power for
the ICU comes from the fuel pump relay instead of the ECU power relay.
Thus in those later models the ISV only hums when the fuel pump is
supposed to be running.

Mark

Neil N wrote:
> In Bentley wiring diagrams for '86, to '90 and up,
> a change in wire gauge aside, I see the same
> wiring scheme from ICU to the ISV.
> On my '88 (which tends to use an '87 wiring diagram),
> the ISV "hums" with key to ign. on, engine off.
> IIRC, on later model years the ISV "hums" only when engine running.
> Possibly ONLY due to a change somewhere else in the wiring harness??
>