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87 Carerra, 3.2 liter en
 
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Help: 1987 911 Getting constant 12 Volts to Headlights even when off

As usual I do not know what I am doing and if you guys can point me in the right direction.

I have a 1987 3.2 Carrera and some years ago I installed a Strosek body kit and used HID bulbs and lights for my headlights. I am now removing all of that and going back to a halogin light kit. But something is wrong in that the wires to my headlights are getting a constant 12 volts even when the lights are not turned on. The bulbs are lit even with the car turned off and the light switch is off.

I went to the fuse panel and fuse 3 and 4 in the third fuse block control the headlights. I have the factory electrical diagrams and have checked all of the wires going to those fuses. the bottom two wires, yellow and yellow/green respectively, both are registering a constant 12 volts with the car and headlight switch being off.

Can anyone let me know what direction I should be looking. I mean the headlights come on but the problem is they are on ALL THE TIME. Maybe I have the wires at the headlight switch crossed---that is what my preliminary research is starting to indicate.

Please put me in the right direction

Charles
Old 07-07-2019, 01:26 PM
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Charles,

Your ground is not good. When electricity flows backward - it's because you don't have a good ground.
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Old 07-07-2019, 04:25 PM
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Quote:
Originally Posted by Walter_Middie View Post
Charles,

Your ground is not good. When electricity flows backward - it's because you don't have a good ground.
Okay Walter can you direct me what ground and where to check, Should I be checking this at the fuse panel (wires or what. I am a little lost here
Old 07-07-2019, 06:13 PM
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Pull the fuses and see if voltage to ground goes away on the bottom but remains on top to ground.
Top of fuse terminal always hot likely means you have wired the switch wrong.
Power flows from the switch to the top fuse terminal of 3 or 4. (Single yellow wire)
(jumper between 3+4 is on back of fuse panel built in)
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Old 07-07-2019, 06:57 PM
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Quote:
Originally Posted by timmy2 View Post
Pull the fuses and see if voltage to ground goes away on the bottom but remains on top to ground.
Top of fuse terminal always hot likely means you have wired the switch wrong.
Power flows from the switch to the top fuse terminal of 3 or 4. (Single yellow wire)
(jumper between 3+4 is on back of fuse panel built in)
Dennis:

Thanks so much for chiming in and providing me guidance on where and how to begin my troubleshooting. Following your instructions here is what I got:

1. I pulled the fuses from 3 & 4 and am getting 12 volts on the top of both 3 & 4. those wires remain hot.

2. Bottom wire of fuse 3 has a ground reading with the fuse pulled

3. Bottom wire of fuse 4 has a ground reading with the fuse pulled

That is where I am at. As I stated in my earlier post the headlights stay on even with the car off and lights turned off. So, I think my problem is as you stated I am constantly getting 12 volts to the top of fuses 3 and 4. Do not know what to make of why I am not getting a ground reading at the bottom of fuse 4

Based on the above readings what do you suggest I do next

Again thanks so much for the troubleshooting guidance

Charles
Old 07-08-2019, 04:56 AM
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I’m confused, you first posted you were seeing ground on both 3 and 4, then ask why no ground on 4?
(You should be measuring through the lamp filament to ground)
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Old 07-08-2019, 06:23 AM
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Quote:
Originally Posted by timmy2 View Post
Iím confused, you first posted you were seeing ground on both 3 and 4, then ask why no ground on 4?
(You should be measuring through the lamp filament to ground)
Timmy:

Bear with me as I have no electrical or mechanical acumen as all of this is new to me. What I can say is I tested the wires at the top of fuses 3 & 4. Both are positive 12 volts with the lights off.

Tested the wires at the bottom of 3 &4 and wire 3 has a ground reading whereas wire 4 has no reading whatsoever.

"(You should be measuring through the lamp filament to ground)". Given my lack of electrical knowledge I do not know what you are directing here. Your directions are like speaking to someone who is electrically knowledgeable, which I am not. Are you stating that I should put the fuses back in and check the top and bottom of the two fuses. If that is what you are saying I will go do this. Please let me know in laypersons terms. Thanks for your patience
Old 07-08-2019, 06:36 AM
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Quote:
Originally Posted by timmy2 View Post
Iím confused, you first posted you were seeing ground on both 3 and 4, then ask why no ground on 4?
(You should be measuring through the lamp filament to ground)
Timmy:

Bear with me as I have no electrical or mechanical acumen as all of this is new to me. What I can say is I tested the wires at the top of fuses 3 & 4. Both are positive 12 volts with the lights off.

Tested the wires at the bottom of 3 &4 and wire 3 has a ground reading whereas wire 4 has no reading whatsoever.

"(You should be measuring through the lamp filament to ground)". Given my lack of electrical knowledge I do not know what you are directing here. Your directions are like speaking to someone who is electrically knowledgeable, which I am not. Are you stating that I should put the fuses back in and check the top and bottom of the two fuses. If that is what you are saying I will go do this. Please let me know in laypersons terms. Thanks for your patience
Old 07-08-2019, 06:42 AM
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Okay Timmy:

I put the fuses back in and at the top of 3&4 fuse I am getting 12.4 volts and at the bottom of 3&4 I am getting 12.4 volts. Where do you see the problem? Does this indicate I wired the headlight switch wrong
Old 07-08-2019, 07:05 AM
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I am at work, so don’t expect immediate reply’s.
Leave the fuses out for now.
If you have worked on the light switch, it is likely you have connected the yellow wire to a constant 12v terminal.
Search the forum for headlight switch connection pictures. They are out there.
Disconnect the battery when under the dash making things right.
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Old 07-08-2019, 07:22 AM
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Dennis:

You are correct as I did do work under the dash to include tampering with the light switch. To be honest I had modified the dash to include all digital and pushbuttons. For the headlights and foglight I have pushbuttons and so that is where the wiring mistakes were made. I did go on the website and found wiring for the headlight switch. I will address the matter from that perspective.

Thanks so much for your guidance and directing me on how to troubleshoot this matter

C
Old 07-08-2019, 07:39 AM
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Quote:
Originally Posted by Walter_Middie View Post
Charles,

Your ground is not good. When electricity flows backward - it's because you don't have a good ground.
i hope you are kidding.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
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Old 07-08-2019, 08:54 AM
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take a look at the light SW and see if you have more than one wire connected to pin 30 or if there is another wire tied in with the large red wire.
you could also remove the red wire from pin 30 and see if the lights go out,.


there is an option for some control unit for the lights, I assume you don't have it.
if you have 2 wires feeding the fuse remove each one one at a time and see which one has power on it. it looks like the one on fuse 3 "should" be from the turn SW.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 07-08-2019, 09:36 AM
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use a test light if you have one.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 07-08-2019, 09:37 AM
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Quote:
Originally Posted by T77911S View Post
take a look at the light SW and see if you have more than one wire connected to pin 30 or if there is another wire tied in with the large red wire.
you could also remove the red wire from pin 30 and see if the lights go out,.


there is an option for some control unit for the lights, I assume you don't have it.
if you have 2 wires feeding the fuse remove each one one at a time and see which one has power on it. it looks like the one on fuse 3 "should" be from the turn SW.
T77911S:

I will get to the Headlight SW and look to see what you describe and let you know,

Thanks so much for weighing in
Old 07-08-2019, 10:16 AM
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Found this in the Pelican Forum. Picture and diagram not mine.
Hope it helps.


Old 07-08-2019, 01:05 PM
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Doporfi:

Yes I had been using that exact chart and pic as a guide. But thanks so much for chiming in.

To everyone:

I am checking the possible sources of my errors. I say this because previously I had been doing a lot of wiring at the fuse panel as well at the headlight switch. Looking back at the work I did at the fuse panel my question to everyone is should the top wires at fuses 3 and 4 have constant 12 volts to them even with the lights and ignition off. That is what I have and I want to make sure I did not wrongly connect a hot wire to those two top wires that are bridged together.
Old 07-08-2019, 01:26 PM
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Quote:
i hope you are kidding.
I had a similar issue with an older vehicle in that a tail light with no power going to it would light up. It was caused by a bad ground and the current flow was finding its own way back through the bulbs.

Current travel direction by convention is from 'positive' higher level to 'negative' lower level.

Backfeeding is flow of electrical energy in the reverse direction from its normal flow.

Bad ground connections can result in circuits finding alternate grounds. Double filament bulbs with a bad ground of one lamp will cause the current to find a ground through the bulb on the opposite side of the car. The bulb can light even when they should not - like when there is seemingly no power to it.
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Old 07-08-2019, 05:27 PM
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Walt,
Pulling the fuses and having power to the top fuse holder and none on the lower going to the lights proves the wiring from the switch area is amiss.
He isn’t searching for ghost voltages at this point in the diagnostics.
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Old 07-08-2019, 06:12 PM
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Okay I found the source of why my lights were staying on continuously.

I had recently converted all of my fuses in the fuse box to the spade fuses (? don't know name) which required me to rewire the entire fuse panel. Dumb me I had a 12 volt dedicated wire I installed connected to the top wires for fuse 3 and 4, which caused me to get continuous 12 volts at those wires. Dumb me.

I am going back and redoing all of the wires in the fuse panel.

The top wire for fuse 3 of the third bank (headlight wire identifies it as a yellow wire with a black strip (that is wire 3 or 4, I think it is 3). But whichever one for the life of me I cannot find a wire that is yellow with a black stripe. I looked for 45 minutes and simply cannot find that wire.

Also, I remember seeing somewhere a source that set forth which wires in the fuse panel have what power going to it (continuous or not). I cannot find that source again. Any help please
Old 07-08-2019, 06:45 PM
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