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Fog light relay just buzzes!
Fog lights never worked, so I thought I'd take a stab at it. Threw a fuse in the correct spot, new relay installed, and... the lights now come on, but the relay just buzzes. That'll fry the relay, obviously, but I really don't where to start.
It's not the relay, other relays swapped out buzz as well. Loose ground somewhere? I can't see what's causing the oscillation... Thanks.
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1984 928s 5 speed |
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05-03-2007, 07:27 PM
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The relay socket is clean/tight.....
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1984 928s 5 speed |
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05-04-2007, 08:59 AM
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Location: New Jersey
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I was just looking at the fog light circuit for an SC. There are a couple of quick checks you can easily do if you have a multimeter. I would test the ground connection from pin 85 on the empty socket to battery ground, should be zero. With the relay still removed I would check the voltage at pin 86 with the foglight switched pulled into the 'on' position and the ignition in the run position. You should see greater then 12 volts with a healthy battery or with the engine running. If the voltage is low then measure the voltage after fuse number 6. The green wire feeds power to the switch. If the voltage is at the correct value, then I would guess that the switch is bad. If the voltage is low then measure the voltage going into the fuse.
The chatter is being caused by not enough voltage being applied to the solenoid coil..so it is not latching so to speak. Causes are a voltage drop before the solenoid or a high resistance to ground after the solenoid. 
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Peace, Ron www.ronorlando.net 78SC Targa 3.2 SS, 964 cams, CIS, SSI's,Dansk Own a gun and you can rob a bank , own a bank and you can rob the world. |
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05-04-2007, 11:52 AM
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OK, so here are my findings:
KEY/SWITCH ON: Pin 85 to gnd= 12v Pin 86 to gnd= 0v Pin 30 to gnd= 12v KEY/Switch OFF: 85 to gnd= o ohms 86 to gnd 0 ohms Funny thing is this, when I put the relay in WITHOUT Fuse 8 installed, it clicks/holds no problem. (no lights, of course, with fuse out). When fuse is in, I get the buzzing again. Voltages seem healthy (though maybe backwards?) and maybe there is a reverse feedback loop completed with the fuse installed. How can I switch it back around?
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05-04-2007, 04:42 PM
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Hmmm..when I got home from work I decided to look in the Bentley for SC's. Then I thought about the possiblity that the OEM circuit was tampered with. The headlight flasher on our cars normally turns the fogs off when the high beams are on. You might want to check to see if someone didn't dick around with the wiring. I will try to trace the wiring for you.
An always hot unfused 12 volts goes to pin 30 of the fog light relay via a red wire. That 12 volts exits the relay socket on pin 87 when the relay contacts close. The wire from pin 87 is White/Green and connects to Fuse 1 [16 amps] on the front fuse panel. It leaves the fuse panel on two white/yellow wires and goes to the fog lights. There should not be any other wires attached to fuse 1. Ok, now the switch side of things gets a bit ugly. Power comes from the ignition switch on a red / white wire to the headlight switch pin 75. Power leaves the headlight switch from pin 56 on a grey wireto pin 56 of the headlight dimmer switch on the steering column. It leaves the headlight dimmer switch from pin 56B via a yellow wire and goes to fuse 6 [8 amps] and from there a grey wire to pin 15 on the fog light switch. From the foglight switch pin 1 power travels thru a blue/white wire to pin 86 of the foglight relay. A common mod was to wire the fogs so that they were independant of the headlight dimmer switch. If someone wired the relay solenoid so that it got its power from fuse 1 then it is possible that when the foglights come on they pull enough current to create a low voltage condition for the solenoid. You should also see what wattage bulbs are installed in the foglight housing. Hope this makes some sense to you.
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Peace, Ron www.ronorlando.net 78SC Targa 3.2 SS, 964 cams, CIS, SSI's,Dansk Own a gun and you can rob a bank , own a bank and you can rob the world. Last edited by Mysterytrain; 05-04-2007 at 06:08 PM.. |
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05-04-2007, 06:02 PM
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Hi Ron,
Many thanks for taking the time to help me on this. That's what makes this board so great. You shed some serious light when you said there should only be two white/yelow wires coming off fuse 1. they were there, along with a white wire that had been added. Looks factory, though.. I removed it and all was dead. Touching it to the fuse contact got me the buzzing again. Time to trace that bastard out... Thanks again. Eric
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1984 928s 5 speed |
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05-04-2007, 06:34 PM
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OK so I moved the Mystery Wire over to the license plate light fuse, and the relay no longer buzzes. The fogs work only when the headlights are in high beam, however....
Sounds like I'm getting closer, but I don't want to have to run high beams to get the fogs to work! Anybody know what "The Mod" is to get the fogs to work totally independently of the headlights?
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1984 928s 5 speed |
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05-04-2007, 07:48 PM
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