Voltage guage suddenly reading low
09-28-2008, 11:14 PM
#1
Rennlist Member
Thread Starter
Voltage guage suddenly reading low
Hi, 1990 S4
On Sunday my voltage guage suddenly started reading just below 12V (RPM independant). With the ignition turned on it barely moves (10V).
I have measured across the hot point in the engine bay & body and got 13.8V & 12.1V respectively.
I recently had all the fuses out looking for a battery drain problem.
I clean the earthing points regularly.
Anyone point me in the right direction as to where to start looking?
Cheers,
Myles
On Sunday my voltage guage suddenly started reading just below 12V (RPM independant). With the ignition turned on it barely moves (10V).
I have measured across the hot point in the engine bay & body and got 13.8V & 12.1V respectively.
I recently had all the fuses out looking for a battery drain problem.
I clean the earthing points regularly.
Anyone point me in the right direction as to where to start looking?
Cheers,
Myles
09-28-2008, 11:40 PM
#2
Rennlist Member
If you've got 12+ volts in your cigarette lighter, but your guage is just showing 10v...then I'd think your cable connection to your instrument circuit panel or the voltage guage itself is gummy.
A little Marine "Corrosion Block" or Stabiliant 22a or De-Oxit should do nicely to get you back to a realistic number, I'd think.
A little Marine "Corrosion Block" or Stabiliant 22a or De-Oxit should do nicely to get you back to a realistic number, I'd think.
09-28-2008, 11:50 PM
#3
With the engine running, check at the front post, as you have done, and check at the battery.
If it's anything like mine and several I've seen, the gauge connections are bad but the alt/battery are fine.
If it's anything like mine and several I've seen, the gauge connections are bad but the alt/battery are fine.
09-28-2008, 11:50 PM
#4
Team Owner
It would be wise to clean the hot post connections and the grounding points under the dash above the CE panel, use a pink eraser disconnect the battery first
09-29-2008, 04:04 PM
#5
Addict
Rennlist Member
Rennlist Member
If the above hasn't worked, I just happened to pull the cluster on my 85 for the same problem. The gauge read low and the reading at the post while running was 13+v. I removed the resistor behind the gauge and took a reading. The resistor is rated at 68 and I got a reading of 77...more than acceptable. Since the number was higher, there is more resistance causing the gauge to read low. The resistor was beyond it's usefulness. Went to a local electronics store and got a pack of 2 resistors for a $1.25. 68R 3w. Gauge works fine now and reads properly.
09-29-2008, 07:00 PM
#6
Race Car
Join Date: Sep 2007
Location: No where Oklahoma AKA "The Dust Bowl" In The Arm pit Of Hell
Posts: 3,663
Likes: 0
Received 0 Likes
on
0 Posts
If the above hasn't worked, I just happened to pull the cluster on my 85 for the same problem. The gauge read low and the reading at the post while running was 13+v. I removed the resistor behind the gauge and took a reading. The resistor is rated at 68 and I got a reading of 77...more than acceptable. Since the number was higher, there is more resistance causing the gauge to read low. The resistor was beyond it's usefulness. Went to a local electronics store and got a pack of 2 resistors for a $1.25. 68R 3w. Gauge works fine now and reads properly.
Great tip should have done it when I pulled the pod a bit ago. My volt meter is still crap.
09-29-2008, 08:28 PM
#7
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Try adjusting the steering wheel height up and down with the engine running.
Sounds crazy, but if the meter changes it means a loose connection on the circuit board.
Sounds crazy, but if the meter changes it means a loose connection on the circuit board.
Trending Topics
09-29-2008, 09:28 PM
#11
Race Car
Join Date: Sep 2007
Location: No where Oklahoma AKA "The Dust Bowl" In The Arm pit Of Hell
Posts: 3,663
Likes: 0
Received 0 Likes
on
0 Posts
I kinda tried that by moving the needle position on the shaft. Dave what year car was that out of or does it apply to all? Also can you explain a bit more of your process?
09-29-2008, 11:17 PM
#12
Rennlist Member
Thread Starter
Thanks all for the replies & suggestions. I will work my way through them from easiest to hardest & let you know how I get on.
Regards,
Myles
Regards,
Myles
10-07-2008, 11:11 PM
#13
Rennlist Member
Thread Starter
I have carried out the following in my search for a fix. No luck yet.
Started car & moved steering wheel up & down - helped a bit.
Removed CE panel & cleaned ground points behind & above it.
Removed POD & checked connections & cleaned them.
Dismantled instrument panel & cleaned connections to the guage itself. I replaced several blown bulbs while I was at it.
Could not adjust guage (different from one in the above pictures).
I could not see the resistor referred to above.
Reassembled car & still reading low (although better than it was).
Any further suggestions?
Cheers,
Myles
Started car & moved steering wheel up & down - helped a bit.
Removed CE panel & cleaned ground points behind & above it.
Removed POD & checked connections & cleaned them.
Dismantled instrument panel & cleaned connections to the guage itself. I replaced several blown bulbs while I was at it.
Could not adjust guage (different from one in the above pictures).
I could not see the resistor referred to above.
Reassembled car & still reading low (although better than it was).
Any further suggestions?
Cheers,
Myles
10-07-2008, 11:52 PM
#14
Race Car
Join Date: Sep 2007
Location: No where Oklahoma AKA "The Dust Bowl" In The Arm pit Of Hell
Posts: 3,663
Likes: 0
Received 0 Likes
on
0 Posts
with mine I just came to the conclusion that it's crap. I've done all this and it's worse than ever
Infact I might just need to buy a new one. Are these still available?
Infact I might just need to buy a new one. Are these still available?
10-08-2008, 02:51 AM
#15
Rennlist Member
The resistor is not related to the voltmeter reading ... Keith, you must have inadvertently fixed a bad connection elsewhere, maybe on an edge connector! 
If you had the gauge out in your hand, you might have tried connecting it to 12V directly to see how close it reads. Be very careful you don't connect it backwards, and be especially careful you don't ground the terminal to the case -- it's very easy to do. Mine was pretty near dead-on when I did this, the problem was in one of the many connections between the gauge and the battery.
A couple of things that led to a cure were cleaning up the CE panel (much more intimidating on a '90!) and refreshing the electrical connections in the pod and at the jump post.
You'll want to be very careful pushing relays in on that later panel, sometimes the plastic gets brittle with age and the sockets push right through!
If you had the gauge out in your hand, you might have tried connecting it to 12V directly to see how close it reads. Be very careful you don't connect it backwards, and be especially careful you don't ground the terminal to the case -- it's very easy to do. Mine was pretty near dead-on when I did this, the problem was in one of the many connections between the gauge and the battery.
A couple of things that led to a cure were cleaning up the CE panel (much more intimidating on a '90!) and refreshing the electrical connections in the pod and at the jump post.
You'll want to be very careful pushing relays in on that later panel, sometimes the plastic gets brittle with age and the sockets push right through!