Date:         Sat, 21 Feb 2009 17:51:37 -0800
Reply-To:     James Ballen <jamosb78@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         James Ballen <jamosb78@YAHOO.COM>
Subject:      Help troubleshoot my instrument cluster
Content-Type: text/plain; charset=us-ascii

Hey folks,

Hopefully some collective wisdom from the group can help me figure out what's going on with my instrument cluster wiring.

I have an '86 wolfsburg weekender that came with an analog clock cluster.
PO installed a cluster from an '85 w/a tach.
Everything works except a few things:

-the coolant temp sensor does not work with the headlight switch turned on.  I had the boys at Buslab fix this about a year ago...Marco told me it was a shorted wire somewhere...and it worked fine until the other day when it started happening again.  Pin #6 on my dash connector (coolant temp sensor) has a wire butt-spliced onto it that goes down to the back, bottom left of the fuse/relay box.  I can't tell exactly what it's plugged into, but I think it's a relay.  Not sure why it's spliced, but it was working fine until a couple days ago.  Temp accuracy was verified with an infared temp gun.

-once the coolant system is nearly up to operating temp, the tach sits up around 4k.  Once the engine is revved up to ~1800 the tach then reads accurately.  As soon as it goes back to idle, the needle shoots back up to 4k.  While it's warming up, the needle reads accurately around 900 at idle, but introducing other electrical loads affects the reading.  For example, if I turn on my headlights, the tach needle jumps up a bit, or if I turn on the turn signal, the tach will bounce in time with the blinking.

-the coolant LED sometimes flashes a longish amount of time upon startup before going out.  I know the coolant level is good.

Things I've done:

I acquired another cluster from another '85 van.
Symptoms are exactly the same.  This should rule out the cluster being the problem...
With my meter, I measured 0 ohms resistance on the pin #3 ground to chasis ground, so the ground should be good...
I unhooked pin #12, the dynamic oil buzzer system, since the '85 cluster doesn't have this function, but there is no change in anything.

I'm sort of at a loss.  That spliced coolant sensor wire may have something to do with the coolant sensor problem, right?

But that still does not explain the tachometer problem.
I've read that there is an oil pressure sensor (I think) that starts engaging after 2k RPM, is this right?  Seems like that could be related to the tach issue since they both relate to 1800-2000 RPM...but I don't know anything about it.

Any suggestions are very welcome.  Please PM me as I am on digest mode and sometimes don't receive posts until a day or two later.
Hopefully I've been specific enough for you to have some ideas...

Thanks!

/james