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Date:         Tue, 4 Jan 2011 14:58:08 -0600
Reply-To:     Tom Hargrave <thargrav@HIWAAY.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tom Hargrave <thargrav@HIWAAY.NET>
Subject:      Re: 87 Cruise Control--followup
Comments: To: David Vickery <david_vickery@YAHOO.COM>
In-Reply-To:  <23041.80691.qm@web32407.mail.mud.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"

David,

The test light will not work as a test jumper because it is designed to light with 12 Volts, so is your vacuum motor.

When you tried using the test light as a jumper you made a series circuit - you applied 12 Volts across the two in series.

This creates a voltage divider where part of the 12 Volts is used by one part of the series circuit and the remaining part is used by the other part in the series circuit.

The actual division is not equal - it depends on the element's resistance or impedance. The element with the highest resistance uses most of the voltage.

In your case, the test light had very high resistance compared to the vacuum motor and most of the 12 Volts was used by the test light.

This left maybe 1 - 2 volts or less for the vacuum motor.

Hope this helps. ;)

Tom www.towercooler.com www.stir-plate.com

-----Original Message----- From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of David Vickery Sent: Tuesday, January 04, 2011 2:31 PM To: vanagon@GERRY.VANAGON.COM Subject: Re: 87 Cruise Control--followup

I wanted to send an update on my cruise control problem for the archives.

Thanks to the couple people that responded to my post. I mentioned it must be difficult to troubleshoot electrical problems on a list because there are so many mistakes a person can make in the testing itself. In my case, I was using a test light but I also used it as the jumper wire when trying to see if the vacuum motor would run. Apparently you can't do that, why I don't know. The test light would light up but the pump would not run. When I used a jumper wire instead of the light, the motor ran.

The real problem turned out to be an intermitent brake cutoff switch. It was passing that tests sometimes and sometimes not. I tested it for continuity and it seemed o.k. so I ignored it. After getting the van back from the shop working, I ran the diagnostics again to see what I was doing wrong.

I posted some of what I learned at thesamba which may help the next person. http://www.thesamba.com/vw/forum/viewtopic.php?t=317214&highlight=

Thanks, Dave in Fort Collins

--- On Sat, 12/25/10, David Vickery <david_vickery@yahoo.com> wrote:

> Well the pump works fine, so it must > be something else.  I connected the pump to the battery > directly and it runs.  BTW, the other wire is for a > valve; it clicks when you give it power like it is supposed > to.  And the pump runs when you connect brown and green > to battery.  The puzzling thing is that I get 12.x > volts at the plug on the same connectors that I connected > straight to the battery, but at the plug it won't run.  > > -- On Fri, 12/24/10, David Vickery <david_vickery@YAHOO.COM> > wrote: > > Hi all, > > > > Hoping someone can help with my 1987 stock cruise > control > > problem. > > > > Background:  My cruise was working well now it won't > > come on.  I went through the Bentley troubleshooting > > diagram with a test light and passed the first > several > > checks, including the tests for the clutch and brake > > switches.  Since I passed those tests, obviously the > > fuse is fine and the on/off button works.  When I > got > > to the test for the vacuum pump motor, jumping #4 pin > with > > ground it says I should hear the pump come on.  I > don't > > hear anything.  With the ignition on and the cruise > > control in the on position, the test light lights up > but no > > sounds from the pump in back. > > > > I tried another pump today (used and unknown > condition) and > > I don't hear anything with it either.  So I am > > wondering if it could be a wiring issue or possibly > the 2nd > > pump is bad.  With the #4 jumper in place and a volt > > meter at the pump in back, I read 12 volts at the plug > using > > + to green wire and negative on the brown wire.  I > > don't know what the green and white wire is for but I > don't > > get 12 volts when I try substituting that for the > green wire > > with my voltmeter.  When I had the pumps out, I > tried > > putting 12 volts to them directly and I don't hear > anything, > > but I am not sure if I should be using the green/white > or > > green or both with brown going to negative. > > > > If anyone knows how I can test the pump directly and > what > > it should sound like if it is working, I would be > very > > appreciative. > > > > Thanks, Dave > > > > > >


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