Dash Voltmeter reads low
Racer
Joined: Mar 2011
Posts: 478
Likes: 1
From: dublin, ireland
your showing your age with the disconnecting the battery lead test,that was used with the old dynamo charging systems that died out to alternators in the 1970's iirrc.
my car does the same reading 1 volt lower than it should all the time i knew it was a common problen...never knew it was adjustable.thanks for the picture.
my car does the same reading 1 volt lower than it should all the time i knew it was a common problen...never knew it was adjustable.thanks for the picture.
Addict
Rennlist Member
Rennlist Member
Joined: Jul 2002
Posts: 2,693
Likes: 52
From: AZ
On my 1979 928 I found that by running a direct 12V supply circuit (relay switched off the ignition to supply voltage) and direct ground circuit I got proper voltage and the temperature gauge is more accurate. The older 928 may have a voltage drop across the connectors to the instrument pod and in the flex circuit itself. Tweaking the volt meter pot may solve the voltage reading but it won't solve the inacurate temperature gauge.
Burning Brakes
Joined: Aug 2009
Posts: 901
Likes: 15
From: San Francisco
What is the purpose of an "adjustable" voltmeter? Is that a 928 exclusive feature?
My 1987 S4 also runs low. I even bought a new battery as I thought it was not holding its charge but it was not the case. Now I know why.
Steve
My 1987 S4 also runs low. I even bought a new battery as I thought it was not holding its charge but it was not the case. Now I know why.
Steve
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Joined: Mar 2002
Posts: 13,657
Likes: 616
From: Phoenix AZ
Voltage drops (due to increased resistance) can be dialed out this way but often the voltage drops themselves are variable due to loading - so they will vary not only with with supply voltage but also with dashboard current loading (think variable lighting) and possibly activation of other equipment that is on the same supply/ground.
You can close major gaps this way but will still have accuracy issues...
As Rich notes it can be due to contact resistance build up somewhere in the chain... so it does makes sense to clean everything well - connector's terminals, switches - but it's more difficult to do than it sounds.
Alan
