Date: Wed, 7 Oct 1998 09:11:05 -0700
Reply-To: YauMan Chan <YauMan@CCHEM.BERKELEY.EDU>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: YauMan Chan <YauMan@CCHEM.BERKELEY.EDU>
Subject: Re: tracing electrical problem
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Ok let's try to do this without getting into Maxwells equations and electromagnetic theory 101! (btw electrons flow from -neg to +pos in the circuit. But by definition, most electronic engineers analysis circuits by assuming current {not electron} flow from +pos to -neg which drives physicists bonkers 'cos that's not how nature works ... but who cares.. electronic engineers are just physicsis who flunk quantum mechanics!)
There are 3 reasons why electric gadets fail: a. power is not getting to the gadet because of bad switch or broken wire., b. the gadet is broken and c. bad ground.
In the case of the mirror, if both mirrors fails, it is probably not the mirror motors (highly improbable both motors failed at the same time.) Since both mirrors are controlled by one switch, it is probably in the switch or in the power or ground wiring.
You need a Voltmeter/Ohmmeter. A cheap one from Radio Slack will do.. as long as you get one with an alligator clip lead and a sharp pin point probe end. You also need your Bently manual.. and learn to read the funcky wiring diagram and try to trace the circuit on the manual. You will notice 3 distinct power circuits (Very top horizontal lines on the bently drawing) Wire 30 is almost always RED and is direct power from the battery. It powers things that can turn on regardless of whether the igniton switch is on or off like interior lights. Wire 15 is usually BLACK and is powered on where the key is in the on OR start position. It is used to power most of the electronics in the engine compartment. Wire X is usually BLACK/YELLOW and is the accessory circuit and is used to power things that can come on only when the key is in the on or accessary position (like blower fan ) but does is turned off when the starter is cranking. I think the power mirror runs of the Wire X circuit. Ground wires are BROWN in German cars.
When you are ready to dive into this, remove the door panel (drivers side) and look for the BLK/YEL wire at the switch. Clip the ground lead of your voltmeter (in 12VDC setting) to a good ground. Now using the sharp probe, prick through the insulation of the BLK/YEL wire closest to the switch. Turn on ignition to on. If you don't see 12+ volts, power is not getting to the mirror. Trace this wire back to the source (looking for breaks or bad connectors at the distribution block)
If the power gets to the switch, then the problem may be at the switch. Remove the switch and check for continunity using the meter set in the OHMs or resistance setting.. use the lowest (or least sensitive) setting ie 0-200 ohms full scale. Look at the bentley drawings of the switch and follow the leads .. which two should read 0 ohms when you move the switch to different possitons.. If the switch fails change the switch.
If the switch works, trace the ground. Again using the OHMmeter, clip one end to a good ground then using the probe, take the resistance reading at the ground terminal of the gadget in question. If the ground terminal do not read 0 ohms with the ground of the van, there is a bad ground. btw, in the case of the mirror, the motor is in series with an electronic clutch.. so the ground of the whole setup is on the clutch side. Also, both mirrors share the same ground.. so if the ground wire is bad, both mirrors will stop working.
Hope this help.
Yau-Man Chan
87 GL
>>> tonyd <tonyd@CANDESA.COM> 10/06 7:00 AM >>>
hi all,
Can someone walk me through the process for tracing a failed electrical
part such as power mirrors? Maybe clue me in on what I would need to do
such a thing. I've checked the fuses and they seem fine, but I am unsure
of how to tell why something isn't working and where to start the
deductive process. I would really appreciate any input from you very
knowledgable folks. I really don't want to tear into my untouched door
panels unless I know what to look for. :) Thanks in advance
TonyD
'87GL
