I think i fried my wiring harness and ECU Please help!!

[denvercoutu]

So i was installing my obd2 wiring harness into my 328i. Hooked everything up but i didnt have any power when i turned the key, thinking i may have one of the three relays in the wrong spot i switched them around. Next thing i know the whole harness is smoking!!! I pop out the relays but its too late. I go to remove the ecu and a massive amount of smoke comes out once i open the panel. Anynody know what i just did? Ground wires are fried in sections of the harness and im pretty sure the ECU is fried. Ehat are those three relays for ?

[328iFun]

This isnt the first time this has happened.

The three relays are:

(From left to right)

Main Relay
Fuel Pump Relay
O2 Heater Circuit Relay

Although the relays look the same, they are not.

You more than likely put the wrong relay into the main circuit relay connected since you describe it frying grounds towards and at the ECU.

You will need purchase another harness and start over. From the sound of it the harness probably could be repaired but I wouldn't risk it. Get a Bentley when doing any type of electrical repairs/replacement.

If you bought a used harness make sure the relays are in the correct connectors before installing it.

[pbonsalb]

I agree. The relays mostly look the same and are mostly 5 prong in the same style as Bosch relays but BMW changes the function of the prongs so you cannot mix and match them. You may end up with ground to power or vice versa, which is probably what happened. It is possible wires in the tray across the top of the motor are melted and shorting now. That is easy to fix -- buy a used wiring harness for $100 and spend half a day installing it. If you fried the inside of your fuse box that is a bigger issue that I have never dealt with.

[XnWarden]

I work in an auto parts store and people come in looking for relays all the time. They get mad and wonder why I suggest staying away from generic replacements and contacting their dealer. Live and learn.

[E36328Coupe]

I work in an auto parts store and people come in looking for relays all the time. They get mad and wonder why I suggest staying away from generic replacements and contacting their dealer. Live and learn.

Most relays have the circuit diagram and pin numbers on the side so they are pretty easy to spot the generic ones and even adapt to.