Two Electrical Problems
12-06-2003, 02:07 AM
#1
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Join Date: Apr 2003
Location: San Francisco, CA
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Two Electrical Problems
Hello to all 928 enthusiasts,
It's an 88 S4 auto...could you please shed some light to my two problems?
About a week ago, I have noticed one of the low beams (the one on the driver side) is no longer working. Both high beams and fog lights are still working fine. My initial thought was that a blown 9004 bulb. After replacing the driver side bulb with a new 9004, the problem remains the same. I then checked the fuses, both left and right sides were okay. Where else should I look? The lever works fine between low and high beam. Can someone share an electrical diagram of the headlight? Or is there one on the Internet website somewhere?
A second electrical problem happened just a few days ago - it was I guess about the HVAC control unit. AC was working fine, blowing cold, until a couple of days ago. The finding from a reputable shop is that there is no 12 volts signal from the control unit (the one in the center console above the radio) to the thermo control switch? when the AC button was depressed. Fan still blows and AC button still lights, but the idle does not change and air is not cold because the AC clutch is no longer engaged without electricity from the hi/low pressure switch from which passing from the thermo control switch. However, when a small jumper wire was connected between the positive pole and the AC clutch, the clutch engaged immediately and cold air came out. The air control unit is only 6 months old and still under warranty. Is there another more likely possibility that the no voltage problem is not caused by the suspected control unit? Again, does anyone know if there is an electrical diagram that illustrates the wiring? Where else should I check in the car?
Many thanks in advance for any of your advices.
Tony
88 S4 automatic
It's an 88 S4 auto...could you please shed some light to my two problems?
About a week ago, I have noticed one of the low beams (the one on the driver side) is no longer working. Both high beams and fog lights are still working fine. My initial thought was that a blown 9004 bulb. After replacing the driver side bulb with a new 9004, the problem remains the same. I then checked the fuses, both left and right sides were okay. Where else should I look? The lever works fine between low and high beam. Can someone share an electrical diagram of the headlight? Or is there one on the Internet website somewhere?
A second electrical problem happened just a few days ago - it was I guess about the HVAC control unit. AC was working fine, blowing cold, until a couple of days ago. The finding from a reputable shop is that there is no 12 volts signal from the control unit (the one in the center console above the radio) to the thermo control switch? when the AC button was depressed. Fan still blows and AC button still lights, but the idle does not change and air is not cold because the AC clutch is no longer engaged without electricity from the hi/low pressure switch from which passing from the thermo control switch. However, when a small jumper wire was connected between the positive pole and the AC clutch, the clutch engaged immediately and cold air came out. The air control unit is only 6 months old and still under warranty. Is there another more likely possibility that the no voltage problem is not caused by the suspected control unit? Again, does anyone know if there is an electrical diagram that illustrates the wiring? Where else should I check in the car?
Many thanks in advance for any of your advices.
Tony
88 S4 automatic
12-06-2003, 08:20 AM
#2
Rennlist Member
Thought I knew the answer - then made the mistake of checking out the 'bible' - current flow diag. 97-285.
Since there's a common ground @ the bulbs, and the hi beam works, seems as if the ground is OK (check continuity @ the 3 pin socket anyway).
If fuses are OK, and both lo/hi beam fuse pairs are fed respectively via single outputs 56a/56b from the 'combo' relay XXIII/XXIV, then there must be correct current flow from the relay ( 3 of 4 filaments are working).
To be sure, check for 12v at the left lo beam fuse (confirm wiring OK between relay output and fuse input on the left side).If 12v is not here, the pb. is between the relay and the left fuse plug: if 12v present, then the pb. is between the fuse & the bulb socket.
So, if there's 12v at the fuse, I'd check continuity from that lo beam fuse to the lo beam pin @ the left bulb socket :
Hope that will allow some light to shine on the pb. - of the lo beam type!
Since there's a common ground @ the bulbs, and the hi beam works, seems as if the ground is OK (check continuity @ the 3 pin socket anyway).
If fuses are OK, and both lo/hi beam fuse pairs are fed respectively via single outputs 56a/56b from the 'combo' relay XXIII/XXIV, then there must be correct current flow from the relay ( 3 of 4 filaments are working).
To be sure, check for 12v at the left lo beam fuse (confirm wiring OK between relay output and fuse input on the left side).If 12v is not here, the pb. is between the relay and the left fuse plug: if 12v present, then the pb. is between the fuse & the bulb socket.
So, if there's 12v at the fuse, I'd check continuity from that lo beam fuse to the lo beam pin @ the left bulb socket :
Hope that will allow some light to shine on the pb. - of the lo beam type!
12-06-2003, 10:03 AM
#3
Rennlist Member
Re. the AC issue. A quick look @ the'88 schematic does show +12v feed fr. pin #6 of the dash mounted control unit to the thermo switch (freeze protection for the evaporator), on to the AC hi/lo press. switch, to the compressor clutch solenoid.
As AC works when jumpered, it would seem that your shop is correct in assessing no controller output: why is that the case?? - could be a loose wire, dead controller,or controller not 'recognizing' any input from the adjacent AC push button: Is there power at the controller? If so, it's a matter of pulling the controller for a check.
As AC works when jumpered, it would seem that your shop is correct in assessing no controller output: why is that the case?? - could be a loose wire, dead controller,or controller not 'recognizing' any input from the adjacent AC push button: Is there power at the controller? If so, it's a matter of pulling the controller for a check.
