Burnt up wire at relay plug...HELP!!!

[cbecker47]

So, every once in a while after my car sits for a few days my 28 gets extremely hard to crank up. The start will spin, and no crank. Then it will start to crank but not turn over. So, I started swapping out relays that that matched the fuel pump relay after referencing both diagrams on the side and when I went to start it up a ton of white smoke came up. Looks like I shorted out or burnt out the green purple wire. If someone can tell me what that goes to and how do i know if i completely fried my wiring harness. Here are the pictures of the burnt wire. Just to try to test it again I went put back the relay that was running well with the car previously. And reconnected the wire that split. I threaded it through and took some electrical tape to reconnect the split wire. Also before when I would tried to start it after a failed attempted i would here a buzz of the fuel pump until i switched the ignition off and it will stop. Now it does not do it. Any advise would be greatly appreciated. Thanks in advance.









Old relay thats been working


New I tried that burned up the wire

[Mike W.]

Man I don't know what you've got going on there. What exactly year and model, they aren't all quite the same.

Green/violet is for the fuel pump but also goes to the 86 terminal of the O2 relay. The relay you pulled out with the 31 pin on it doesn't look familiar, the one you replaced it with is a main relay, not a fuel pump relay that I'm aware of. The main relay is a specific relay that is the only one on the car like that. I pulled up an 85, 535i wiring diagram since I think I see a M30 oil filter housing down there, but I'm not seeing a relay socket with those wire colors. Need more info, or RonW might pop in and he knows all of this in his head. Is the color code on that one heavy wire in the middle Yellow/violet like it looks? A picture of the wiring diagram of the black relay would help too, the 1 710 565 relay.

And please, please, for your sake, do more than twist wires together and tape them where they burned thru. It will cause you endless grief if you don't at least solder and heat shrink tape them, or ideally replace the terminal in the relay socket, which is actually very easy to do.

[demetk]

Quite obvious that the new relay you tried is does not have the same pin locations as your old relay. Now in order to figure out how extensive the damage is you're going to have to peel back the harness cover. If the damage is limited only to the engine harness then replacing it may be your best bet.

[cbecker47]

Quite obvious that the new relay you tried is does not have the same pin locations as your old relay. Now in order to figure out how extensive the damage is you're going to have to peel back the harness cover. If the damage is limited only to the engine harness then replacing it may be your best bet.

Is there a way to test the wire if it has voltage that runs through it?

[cbecker47]

Man I don't know what you've got going on there. What exactly year and model, they aren't all quite the same.

Green/violet is for the fuel pump but also goes to the 86 terminal of the O2 relay. The relay you pulled out with the 31 pin on it doesn't look familiar, the one you replaced it with is a main relay, not a fuel pump relay that I'm aware of. The main relay is a specific relay that is the only one on the car like that. I pulled up an 85, 535i wiring diagram since I think I see a M30 oil filter housing down there, but I'm not seeing a relay socket with those wire colors. Need more info, or RonW might pop in and he knows all of this in his head. Is the color code on that one heavy wire in the middle Yellow/violet like it looks? A picture of the wiring diagram of the black relay would help too, the 1 710 565 relay.

And please, please, for your sake, do more than twist wires together and tape them where they burned thru. It will cause you endless grief if you don't at least solder and heat shrink tape them, or ideally replace the terminal in the relay socket, which is actually very easy to do.

Yes I am going to be soldering the wires together as well as heat shrinking, do you know how I would be able to test the terminal or the wire. Do I just switch my mulitmeter to volts and test the wire with ignition on?

[Mike W.]

Yes I am going to be soldering the wires together as well as heat shrinking, do you know how I would be able to test the terminal or the wire. Do I just switch my mulitmeter to volts and test the wire with ignition on?

Yes, but... You would normally check between the terminal and ground, but it gets more complicated with a relay in there, you need to check from what the relay switches to on, to ground. But also, after checking for voltage and finding none, check resistance from there to ground. But be careful on that, I've burned up and or blown more than one fuse over the years forgetting to switch back from resistance to voltage. Yes, it can get complicated.

[cbecker47]

Yes I am going to be soldering the wires together as well as heat shrinking, do you know how I would be able to test the terminal or the wire. Do I just switch my mulitmeter to volts and test the wire with ignition on?

Yes, but... You would normally check between the terminal and ground, but it gets more complicated with a relay in there, you need to check from what the relay switches to on, to ground. But also, after checking for voltage and finding none, check resistance from there to ground. But be careful on that, I've burned up and or blown more than one fuse over the years forgetting to switch back from resistance to voltage. Yes, it can get complicated.

Not to sound any stupider than I feel like I do already, I would take my leads my + to the bottom of the terminal with the relay still attached and ignition on and take my negative lead and ground it to check voltage?

[cbecker47]

So...when I got home today with a battery reading of 11.7-11.9 volts, I try to start my car and on the first crank it starts right up no problems at all idles fine. Got a reading on the battery it’s at 13.7-13.9. So yeah not sure what’s going on but it’s running again for now.

[tn535i]

Sorry if you take offense but the phrase "better to be lucky than good" comes to mind. Correct me if I am wrong but that must be the O2 sensor heater relay socket since it has no red wire? I would leave that relay OUT until you are sure what's going on.

Perhaps your fuel relay is still fine but power from the fuel relay goes over to the O2 relay and something must have been shorted to ground. Between the two sockets or after the O2 socket.

BMW sort of screwed up IMO. Fuses are meant to protect wires from overloads but in this case when the fuel relay is energized the power comes right from the battery with many amps available but NO protection on that green/purple wire. The Grn/Prp feeds the O2 relay trigger and then Fuse #1 for the pumps so protection is AFTER the relay.

And your fuel pump should never be running unless the engine is turning so that buzz you heard was either the ICV or a bad relay leaving the pumps energized when it should not have.

If you isolate that burned up wire (and any others) and have the right Fuel relay the car should run I think even if you don't reconnect. Although as you see multiple Grn/Prp wires it may cascade through the O2 relay socket before going to Fuse #1. In that case it needs a good connection but still no O2 relay to run.

All these things are easy as pie to test and you can follow ever wire in the ETM at Wedophones. Learning to use a DMM is mandatory for one of these cars IMO and perhaps someone could put up a link to a decent tutorial on that. I get tired of trying to describe how to use one.