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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: maynardjr on October 12, 2020, 04:45:46 PM
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I am planning on installing fog lights on my 1991 K75S. A previous owner apparently had auxiliary lighting and removed it: There is a pair of red/black wires in the fairing under the headlight that are connected to the OEM auxiliary light switch. I'm trying to figure out if I should use that wiring, or tear it out and wire it myself. I'm leaning very heavily toward re-wiring it myself, but I wanted to see if I'm missing something through my lack of experience with automotive relays.
The good: The switch controls the voltage on the red wire--it is 12V when the switch is on. The black wire is grounded. The PO used a relay, so the current is not flowing through the switch.
The bad: I've traced out the relay wiring, shown the diagram below. The relay is wired completely backwards from every diagram that I've seen: pin 85 goes to +12V instead of ground, while 86 goes to ground through the switch. Pin 30 goes to the light instead of coming from the battery, while 87 is connected to the battery's positive terminal. The fuse is between the relay and the light rather than between the relay and the battery positive connection.
The ugly: The PO was very fond of red wires, although he occasionally connected red wires to black wires, picture attached. The combinations occasionally are connected to ground, and sometimes to +12V. My favorite is a red/black connection made with a female spade connector (turns out that's ground).
So is this some totally backwards wiring that just happens to work by accident, or is this an uncommon but still acceptable arrangement of wiring up the relay?
A minor note but perhaps pertinent: Because the circuit uses the unswitched 12V from the connector for special equipment, the lights will come on without the key being turned on. I'm going to change that so that the fog lights can only be used when the low beams are on due to some rules of the state of Virginia.
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If it were me, I'd start from scratch... remove what the PO installed and then re-install it how you are familiar, and with the colors that make sense for you.
Brown is the standard color on these bikes for ground.
Having it your way, will make it much easier and less head-scratching for you in the future when you have to work on it.
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No brainier. Rip out the shady po stuff and start over.
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Replace that wiring as it's messy and difficult to trace. Use the below schematic as a starting point which allows you to reuse the parts you have.
(http://images42.fotki.com/v1379/photos/3/36012/5049973/DrivingLightRelay-vi.jpg) (https://forums.bmwmoa.org/showthread.php?33889-wiring-relay-additional-driving-lights)
This circuit will only allow the auxillary lights to come on with the ignition even though it is fed from constant +12V. The auxillary lights can be switched on independant of the main headlight, but derives its control from the headlight switch.
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Robert's schematic is the way to go. The only thing I change for my bikes is that I don't use the low beam feed. Rather I go to 12v that is switched on with ignition switch. That allows me to have the lights on all the time during daylight, and then I use the high beam feed at night so I don't blind oncoming drivers while still having the extra light when the high beam is lit.
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maynardjr: About your comment on the wiring being backwards. It doesn't really matter from an electrical standpoint whether the power feed is on pin 30 or pin 87 when it comes to a single-pole single-throw switch as used in this circuit. It does matter if the circuit were to be based off of a single-pole double-throw switch, where there are normally closed (87A) and normally open (87) contacts. Pin 30 is always common and convention dictates that power feeds be made available on the common pin.
For the coil pins, 85 and 86, polarity really doesn't matter at all.
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Thanks for the feedback, everyone! As I said in the original post, I'm leaning heavily toward re-wiring it. Now I feel more strongly that that's the way to go.
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One more question: Does anyone know what style of connector the "Connection for special equipment" uses? When I re-wire the lights, it would be nice to use that connector as is, rather than pulling the required wires out of it. I did a few searches to try to find the connector type, but I wasn't able to find it.
Here's a picture of it, taken from https://forums.bmwmoa.org/showthread.php?4565-Name-that-unused-Electrical-connector
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You could try to find a mate for that 30 year old connector; it would be a May and December wedding. Instead, you could simply tap into its wires without extracting them, or substitute the six position model of these (https://www.easternbeaver.com/Main/Elec__Products/Connectors/Sealed/YPC/ypc.html) if you're attracted to the cylindrical style. icon_cheers
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I wired my aux running lights into the "Connection for special equipment" socket using some single-pole female connectors that fit the male pins. I covered the female fitting with a couple layers of heat shrink tubing for insulation.
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I don't imagine you are going to use that connector for anything as it was intended, I'd just cut off the wires you need to use from the connector and go on. IIRC the "special equipment" was an OEM anti-theft alarm system.
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Somewhere on this forum (or k100) I read that the optional plug (anti theft) is the same as the old cb microphone plug. Dunno if that's right tho, but looks about right. I think it's the white plug, which the wiring colour codes will confirm. It also looks like the plug for the early model fuel tank.
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One more thing to add: I looked at the K75 wiring diagram today and found that the "+12V unswitched" on the special equipment plug is fused in the fuse box. So I feel a bit better about the fuse the PO added being between the relay and the light rather than on the incoming power.
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One more question: Does anyone know what style of connector the "Connection for special equipment" uses? When I re-wire the lights, it would be nice to use that connector as is, rather than pulling the required wires out of it. I did a few searches to try to find the connector type, but I wasn't able to find it.
Here's a picture of it, taken from https://forums.bmwmoa.org/showthread.php?4565-Name-that-unused-Electrical-connector
I've seen a cable which'll mate to this at www.tills.de - look under ELECTRICAL for the "K Kabel" aka the K Cable.
Hope this helps.