S type electrics
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S type electrics
Hi all. I have just fitted a set of parking sensors to my recently acquired s type (2003) sport. Having made a good job of fitting them I then moved on to connecting them. The instructions state that I should find a +ve feed from the reverse light, side light and stop light as well as a feed from an accessory circuit.
Is that laughter I can hear? As those of you that have entered into the world of s type electrics will now tell me that is a very difficult task. Once the ignition is switched on, all 7 wires that lead to the OS rear light cluster all become live. And then when I select reverse, on of them then loses it's current. Now I am totally bewildered. Can any one advise me as to what I may do to find the required +ve feeds, and thereby restore my sanity?
Many thanks TH
Is that laughter I can hear? As those of you that have entered into the world of s type electrics will now tell me that is a very difficult task. Once the ignition is switched on, all 7 wires that lead to the OS rear light cluster all become live. And then when I select reverse, on of them then loses it's current. Now I am totally bewildered. Can any one advise me as to what I may do to find the required +ve feeds, and thereby restore my sanity?
Many thanks TH
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Joined: Oct 2007
Posts: 239
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From: Pittsburgh, PA
RE: S type electrics
Tony,
Your issue may not be as bad as it seems.
One terminal of each rear lamp is fed with +12V when the ignition is switched on while the other terminal of each lamp is "floating" (i.e., not connected) or is connected to chassis ground through a solid state switch in the rear light module. I assume you measured the voltage at each of the 7 wires with respect to chassis ground. When you selected reverse, the rear light module effectively connected one wire of the reverse lamps to chassis ground, which lights the lamp and also causes the voltage measured at the wire that was grounded to go to zero. If you measure the voltage across the two wires to the revese lamp, you would see +12 V when the revese lamp is lit.
It appears that the controller for the rear parking sensors wants to "know" when the transmission is in reverse (for obvious reasons), when the lights are on (unknown reason), and when the brakes are applied (probably used to determine that the velocity of the car is decreasing). The "feed from 12V auxiliary circuit" supplies power to the electronics and sensors when no lamps are on. Depending on how the module is designed, there are two possibilities: (1) you may need to add two small relays to isolate and invert the logical sense of the "reverse" and "stop" signals to the controller , or (2) you can obtain the "reverse" and "stop" signals directly from the voltage across each of these lamps. More information on this system would be helpful to decide the next step. Are the instructions for the parking sensor system available on line? Can you supply a link?
Mark C
Your issue may not be as bad as it seems.
One terminal of each rear lamp is fed with +12V when the ignition is switched on while the other terminal of each lamp is "floating" (i.e., not connected) or is connected to chassis ground through a solid state switch in the rear light module. I assume you measured the voltage at each of the 7 wires with respect to chassis ground. When you selected reverse, the rear light module effectively connected one wire of the reverse lamps to chassis ground, which lights the lamp and also causes the voltage measured at the wire that was grounded to go to zero. If you measure the voltage across the two wires to the revese lamp, you would see +12 V when the revese lamp is lit.
It appears that the controller for the rear parking sensors wants to "know" when the transmission is in reverse (for obvious reasons), when the lights are on (unknown reason), and when the brakes are applied (probably used to determine that the velocity of the car is decreasing). The "feed from 12V auxiliary circuit" supplies power to the electronics and sensors when no lamps are on. Depending on how the module is designed, there are two possibilities: (1) you may need to add two small relays to isolate and invert the logical sense of the "reverse" and "stop" signals to the controller , or (2) you can obtain the "reverse" and "stop" signals directly from the voltage across each of these lamps. More information on this system would be helpful to decide the next step. Are the instructions for the parking sensor system available on line? Can you supply a link?
Mark C
ORIGINAL: tony.harper
The instructions state that I should find a +ve feed from the reverse light, side light and stop light as well as a feed from an accessory circuit.
Once the ignition is switched on, all 7 wires that lead to the OS rear light cluster all become live. And then when I select reverse, on of them then loses it's current.
Many thanks TH
The instructions state that I should find a +ve feed from the reverse light, side light and stop light as well as a feed from an accessory circuit.
Once the ignition is switched on, all 7 wires that lead to the OS rear light cluster all become live. And then when I select reverse, on of them then loses it's current.
Many thanks TH
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