do i have a short of ground problem?, voltage drop when brake is pushed in |
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do i have a short of ground problem?, voltage drop when brake is pushed in |
DRPHIL914 |
Mar 23 2011, 05:55 PM
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#1
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
Voltage drops from 13 to 12 on center console voltage gauge when brake is pushed in. Where do I look first? 75 2.0
Phil |
SLITS |
Mar 23 2011, 05:58 PM
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#2
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"This Utah shit is HARSH!" Group: Benefactors Posts: 13,602 Joined: 22-February 04 From: SoCal Mountains ... Member No.: 1,696 Region Association: None |
Probably all the chassis grounds.
Mine have done the same ... you're powering lights up and they draw volts ... Being a barbarian, I ignore it. |
windforfun |
Mar 23 2011, 06:00 PM
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#3
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Senior Member Group: Members Posts: 1,789 Joined: 17-December 07 From: Blackhawk, CA Member No.: 8,476 Region Association: None |
Voltage regulator?
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McMark |
Mar 23 2011, 06:08 PM
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#4
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
Normal. Cleaning grounds and other electrical connections is a GREAT way to 'spiff up' the electrical system. But because of the way that the voltage meter is wired into the system, it's normal for it to drop as higher wattage systems are enabled (wipers, headlights, blowers, etc).
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orange914 |
Mar 23 2011, 06:09 PM
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#5
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http://5starmediaworks.com/index.html Group: Members Posts: 3,371 Joined: 26-March 05 From: Ceres, California Member No.: 3,818 Region Association: Northern California |
does the voltage drop with other electrical loads also? if so load test the battery, even if it's weak (which would do what you're seeing), do a voltage drop on all grounds also.
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rwilner |
Mar 23 2011, 06:16 PM
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#6
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No Ghosts in the Machine Group: Members Posts: 953 Joined: 30-March 10 From: Boston, MA Member No.: 11,530 Region Association: North East States |
I agree with McMark -- normal. At least, mine does the same thing. My needle jumps around when i turn on my turn signals too.
I think it's an advantage actually -- when the voltage drops you know your brake lights came on, which means the brake light switch on your pedal cluster is properly adjusted! |
Valy |
Mar 23 2011, 06:31 PM
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#7
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Senior Member Group: Members Posts: 1,675 Joined: 6-April 10 From: Sunnyvale, CA Member No.: 11,573 Region Association: Northern California |
Voltage drops from 13 to 12 on center console voltage gauge when brake is pushed in. Where do I look first? 75 2.0 Phil Some small drop is perfectly normal. I would expect the biggest drop when you hit the horn or high beam. To diagnose better, you can check the voltage drop on the regulator itself. If none, clean the ground straps. If the drop is the same there, check the wires to the alternator. A voltage meter is misleading a bit If you have an ampere-meter, you could monitor the charging state of your battery and realize if the alternator is keeping-up with the current load. |
ripper911 |
Mar 23 2011, 06:41 PM
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#8
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corde pulsum tangite Group: Members Posts: 2,920 Joined: 25-April 10 From: Powder Springs, GA Member No.: 11,654 Region Association: South East States |
The voltmeter is wired through the brake light circuit, it's normal to see a drop in voltage.
I also see it as an advantage, I look at the gauge to make sure my brake lights are working. |
Mike Bellis |
Mar 23 2011, 07:50 PM
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#9
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None |
Totally normal. Turn on the turn signal and have some real fun... up, down, up, down, up, down...
Corrosion on the ground points and within the wires them selves. Top that off with rust at each welded seam. The chassis only makes its ground path through tiny little spot welds. To avoid the drop, run a new wire directly to the battery. |
windforfun |
Mar 23 2011, 08:21 PM
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#10
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Senior Member Group: Members Posts: 1,789 Joined: 17-December 07 From: Blackhawk, CA Member No.: 8,476 Region Association: None |
Corrosion within the wires is an interesting possibility. I've seen this in home speaker wire. I haven't yet seen this in my 914. Not yet anyway.
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DRPHIL914 |
Mar 23 2011, 08:27 PM
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#11
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Dr. Phil Group: Members Posts: 5,766 Joined: 9-December 09 From: Bluffton, SC Member No.: 11,106 Region Association: South East States |
Totally normal. Turn on the turn signal and have some real fun... up, down, up, down, up, down... Corrosion on the ground points and within the wires them selves. Top that off with rust at each welded seam. The chassis only makes its ground path through tiny little spot welds. To avoid the drop, run a new wire directly to the battery. Yep, exactly. Also noticed the same with the signals as well. Nice to know i'm not alone. I'll still take a look at the v.r.and grounds but seems to be running great otherwise. And 32 mpg on first tank of gas since setting valves and timing. That's drivig to and from work 20 miles @ 35-45mph. Pretty good I guess, - anyway thanks for the input! |
r_towle |
Mar 23 2011, 08:48 PM
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#12
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Custom Member Group: Members Posts: 24,574 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
rear tail light bulb sockets and the associated ground in the trunk.
Both need to be cleaned up and cleaned out (sockets) every 40 years. rich |
ConeDodger |
Mar 23 2011, 09:36 PM
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#13
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Apex killer! Group: Members Posts: 23,589 Joined: 31-December 04 From: Tahoe Area Member No.: 3,380 Region Association: Northern California |
Normal. Cleaning grounds and other electrical connections is a GREAT way to 'spiff up' the electrical system. But because of the way that the voltage meter is wired into the system, it's normal for it to drop as higher wattage systems are enabled (wipers, headlights, blowers, etc). I remember calling McMark when I noticed this on my own car. I think he told me to keep my eyes on the road! (IMG:style_emoticons/default/blink.gif) (IMG:style_emoticons/default/agree.gif) Normal. I use a very small battery called an Oddesey and it doesn't cause a problem... It never drops below 12V with the headlights, fog lights, brake lights and, turn signals on at the same time. It's just normal draw. |
Mike Bellis |
Mar 23 2011, 09:57 PM
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#14
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None |
Corrosion within the wires is an interesting possibility. I've seen this in home speaker wire. I haven't yet seen this in my 914. Not yet anyway. Start exploratory surgery on your wire harness. Anything other than shiny copper is corrosion. Automotive insluation is cheap and pourus. Moisture gets in and the copper turns black. Wire actually has a life cycle. Our cars are way pass the life cycle of the electronics. OK, don't actually cut into your harness. There is corrosion there, you just haven't found it yet... |
Woody |
Mar 24 2011, 06:38 AM
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#15
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Sandbox Rabblerouser and head toilet scrubber Group: Members Posts: 3,858 Joined: 28-December 10 From: San Antonio Texas Member No.: 12,530 Region Association: Southwest Region |
Excessive resistance through the brake light switch? My car was doing this, brake lights were very dim and the switch was very hot to the touch. I pulled the switch off, opened it and cleaned the contacts.
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sean_v8_914 |
Mar 24 2011, 07:17 AM
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#16
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Chingon 601 Group: Members Posts: 4,011 Joined: 1-February 05 From: San Diego Member No.: 3,541 |
most of the advise above is good but I recomend starting in teh fuse panel first
4th fuse from teh right is corroded ...they are all corroded and dirty. wipe the fuse ends on a green scotch bright pad. only wipe in ONE DIRECTION to prevent the fuse from coming apart. apply very light presure. should be clean in about 5 swipes then clean the copper contacts. that should fix many minor issues, if not proceed to the lamp sockets and chassis grounds do the batt to chassis gnd first, then teh chassis to trans gnd strap |
sean_v8_914 |
Mar 24 2011, 07:17 AM
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#17
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Chingon 601 Group: Members Posts: 4,011 Joined: 1-February 05 From: San Diego Member No.: 3,541 |
like Rich said, " once every 40 years"
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r_towle |
Mar 24 2011, 11:06 AM
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#18
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Custom Member Group: Members Posts: 24,574 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
like Rich said, " once every 40 years" I just find it funny that alot of the issues that come up are 40 year issues. Dirt, corrosion etc. First time I did the rear tailight sockets I was shocked at how much crap was in there...I even looked into buying new sockets to replace them. that was after chasing all the circuits..fuses etc... A few minutes with a dremel/wire brush and some dielectric grease...done. I now just do it whenever I get a new car....all them porsches seem to lack a decent enough ground....and it creates loads of corrosion over the 40-50 years of never being cleaned. First thing I do now...find, remove, and clean all the grounds. There are what...10 maybe...I think there are less, but its pretty simple to do once you have the dremel setup... Distributor grease....same deal. I chased this for a long time...replaced all sorts of stuff on both the ignition and FI...turns out it was just dirty advance plates. Sometimes the answers you get here may be short and sweet, but I agree with everything above...and it comes from all our collective wasted time chasing ghosts. Rich |
jsayre914 |
Mar 24 2011, 11:14 AM
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#19
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Speed Up !!! Group: Members Posts: 3,188 Joined: 10-February 08 From: Timonium MD 21093 Member No.: 8,696 Region Association: MidAtlantic Region |
is there a way to take one of the wires off the back of the guage and wire it directly so that it is not on that circuit. I also was wondering that? My guage does the same thing.
My guage rests just under 14 since i upgraded the electrical system, and it drops to 12.5 w/ the brakes on. (IMG:style_emoticons/default/confused24.gif) |
r_towle |
Mar 24 2011, 11:23 AM
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#20
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Custom Member Group: Members Posts: 24,574 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
What gauge?
If you unplug the volt gauge....life goes on and the car runs fine. If you want it on another circuit, just sire it to another circuit. Its a simple setup...I think post 73 all the cars had the wiring for the gauge in the center console...some cars (mine) had no console... Should be a plug you can unplug right under the flat shifter panel cover...just pull it up and unplug the gauge.. Rich |
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