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I have an 85 535i that has a seemingly dead OBC. Nothing happens with it. There is power to plug, but the OBC relay.... under dash, that has the green 4 prong plug, has two wires cut. Why would somebody do that? Is that why the OBC is not working?

I have searched archives, If I missed it, I apologize.....

Warren

Are they just cut or cut and spliced together? There is a "fix" for a bad OBC relay that cuts two green wires and splices them together. Do you have the ETM for your car? This will give the specific wiring diagram for your model/year and you canidentify the cut wires.
Found the link:
http://wedophones.com/BMWManualsLead.htm

^^ this, and those cut wires shouldn't have any effect on the OBC. Pull the OBC and check the connector on the back.

wrnmnro wrote:I have an 85 535i that has a seemingly dead OBC. Nothing happens with it. There is power to plug, but the OBC relay.... under dash, that has the green 4 prong plug, has two wires cut. Why would somebody do that?

If the OBC were telling the car to not start, cutting either the red & white wire or the brown & green wire would allow the car to start.

wrnmnro wrote:Is that why the OBC is not working?

Cutting wires to the OBC relay would not prevent the OBC from working. It would only prevent the OBC's theft deterent features from working.

wrnmnro wrote:I have searched archives, If I missed it, I apologize.....

Warren

What colors are the cut wires? Options are:
Connector C1 pin 2: Brown & Violet (OBC horn relay control, grounded to sound horn)
Connector C1 pin 3: Red & White (OBC relay power, from fuse 5)
Connector C1 pin 4: Brown & Green (OBC code relay control, grounded to prevent car from starting)
Connector C2 pin 1: Brown & Yellow (OBC horn, connected to C2 pin 2 when C1 pin 2 is grounded)
Connector C2 pin 2: Brown (OBC horn ground)
Connector C2 pin 3: Green (Ignition, disconnected from C2 pin 4 when C1 pin 4 is grounded)
Connector C2 pin 4: Green & Red) (Power to main relay, disconnected from C2 pin 3 when C1 pin 4 is grounded)

Are you sure the OBC itself is nonfunctional? The backlight bulbs for the display are a common failure item. The display is still there, but without light behind it it's really difficult to see.

Shine a bright light at it. If you can see the time on the screen (or simply "uhr") then the light bar is bad and the OBC actually works.

RonW wrote:

wrnmnro wrote:I have an 85 535i that has a seemingly dead OBC. Nothing happens with it. There is power to plug, but the OBC relay.... under dash, that has the green 4 prong plug, has two wires cut. Why would somebody do that?

If the OBC were telling the car to not start, cutting either the red & white wire or the brown & green wire would allow the car to start.

wrnmnro wrote:Is that why the OBC is not working?

Cutting wires to the OBC relay would not prevent the OBC from working. It would only prevent the OBC's theft deterent features from working.

wrnmnro wrote:I have searched archives, If I missed it, I apologize.....

Warren

What colors are the cut wires? Options are:
Connector C1 pin 2: Brown & Violet (OBC horn relay control, grounded to sound horn)
Connector C1 pin 3: Red & White (OBC relay power, from fuse 5)
Connector C1 pin 4: Brown & Green (OBC code relay control, grounded to prevent car from starting)
Connector C2 pin 1: Brown & Yellow (OBC horn, connected to C2 pin 2 when C1 pin 2 is grounded)
Connector C2 pin 2: Brown (OBC horn ground)
Connector C2 pin 3: Green (Ignition, disconnected from C2 pin 4 when C1 pin 4 is grounded)
Connector C2 pin 4: Green & Red) (Power to main relay, disconnected from C2 pin 3 when C1 pin 4 is grounded)

solid green and green/red wire is snipped......

Those are the OBC relay bypass wires. They are supposed to be spliced together for the car to run.

jimoreno wrote:Those are the OBC relay bypass wires. They are supposed to be spliced together for the car to run.

Car starts fine...on the OBC relay box, there are two green plug-ins...the one we are talking about has been snipped right at the base of the box and the two wires taped up with electrician's tape. What would happen if I hooked them back together? Would I get my OBC back?...Why would someone in the past...do this??

Thanks for all your help

wrnmnro wrote:solid green and green/red wire is snipped......

Ok, so the green wire and the green & red wire coming out of the OBC relay are clipped, but I bet the wires on the other side of the clips – the car side, if you follow me – are crimped together. Otherwise, the car definitely won't start.

So the likely possibilities are:
1. The OBC is wrongly telling the OBC relay box to not allow the car to start.
2. The OBC relay box is faulty.

With the car off, get an ohmmeter. The green and green & red wires coming out of the OBC relay box should be shorted together. If they aren't, the OBC relay box is faulty. If the are shorted together, the OBC is probably faulty (i.e. #1 above).

RonW wrote:

wrnmnro wrote:solid green and green/red wire is snipped......

Ok, so the green wire and the green & red wire coming out of the OBC relay are clipped, but I bet the wires on the other side of the clips – the car side, if you follow me – are crimped together. Otherwise, the car definitely won't start.

So the likely possibilities are:
1. The OBC is wrongly telling the OBC relay box to not allow the car to start.
2. The OBC relay box is faulty.

With the car off, get an ohmmeter. The green and green & red wires coming out of the OBC relay box should be shorted together. If they aren't, the OBC relay box is faulty. If the are shorted together, the OBC is probably faulty (i.e. #1 above).

Thanks for the knowledge...but I am a bit confused.
1) the car side...does that mean the other end of the snipped wires from the relay box?
2) the car starts with wires cut...when you say shorted out...what does that mean? not sure how the ohm meter comes into play.
3) there is nothing from the OBC power wise....
Sorry I am slow at wires and currents

These have absolutely nothing to do with your OBC working or not. If you car starts fine, leave them alone.

wrnmnro wrote:solid green and green/red wire is snipped......

RonW wrote:Ok, so the green wire and the green & red wire coming out of the OBC relay are clipped, but I bet the wires on the other side of the clips – the car side, if you follow me – are crimped together. Otherwise, the car definitely won't start.

So the likely possibilities are:
1. The OBC is wrongly telling the OBC relay box to not allow the car to start.
2. The OBC relay box is faulty.

With the car off, get an ohmmeter. The green and green & red wires coming out of the OBC relay box should be shorted together. If they aren't, the OBC relay box is faulty. If the are shorted together, the OBC is probably faulty (i.e. #1 above).

wrnmnro wrote:Thanks for the knowledge...but I am a bit confused.
1) the car side...does that mean the other end of the snipped wires from the relay box?

When one of the wires to the OBC relay box is cut, it turns into two pieces of wire. One piece is connected to the OBC relay box, and the other piece is connected to the rest of the car. The "rest of the car" piece is what I'm referring to when I say "the car part".

wrnmnro wrote:2) the car starts with wires cut...when you say shorted out...what does that mean? not sure how the ohm meter comes into play.

When I said "shorted together" I meant that normally the OBC relay box should connect the green wire to the green & red wire. It does this even when the car is off. Connecting these two wires together allows the car to start. The ohmmeter lets you to see if this is really happening. With the car off, just connect one lead of the ohmmeter to the green wire from the relay box, and the other lead to the green & red wire from the relay box. The meter should show that the two wires are connected, i.e. it will read less than 1 ohm. If they are not connected it will show infinite ohms, or a very high reading, like several megaohms.

wrnmnro wrote:3) there is nothing from the OBC power wise....

I'm not sure what you mean by this. Nothing in the OBC display? The OBC keyboard doesn't light up? The only signals from the OBC to the relay box are the brown & violet wire and the brown & green wire.

wrnmnro wrote:Sorry I am slow at wires and currents

Never too late to learn.

I have hooked it all back up...like I it was... wished I had the OBC...but maybe a little over my head...Can't just buy another and then find out those clipped wires come into play. In the past 2 days I have gained...flashers, turn signals.rear window heater, radio. cleaned up all the grounds, replaced bulbs in dash, tail lights and various other petty but important tasks. The car is coming along nicely...I just do not like leaving a known problem out there.

Thanks to all for valuable input...