Mystery Relay!

[ascott430]

Hey Guys,
Just a quick question. Curious as to what a certain relay is for. It is located outside the fuse box in that group of 3 relays including the fuel pump relay. Looking at the engine bay from the drivers side it is the furthest right of the three and also the largest. What is this relay for. I have a cable running to it which is not connected to anything and I figured this would help me diagnose the problem.

[thejlevie]

The three relays mounted on the left side strut tower are the main, fuel, and O2 heater relays. Since the relay sockets clip into the bracket, there is no assurance that they are in the original configuration and you have to go by the wire colors to know which relay is which (see http://wedophones.com/BMWManualsLead.htm). The original configuration would have the main relay closest to the front of the car and the O2 heater relay closest to the firewall.

[ascott430]

Great Thanks. I know that the fuel relay is furthest left so that only leaves one big and one smaller relay. Would the main relay be the biggest one of the three?

[thejlevie]

Having not had my hands on a 318 in a long while, I don't remember if those relays are the same size, like they are in a 325e/i/is. The wiring diagrams have wire colors for each of the relays and you can identify them that way. That should also tell you what that odd wire is.

[RomeoMike]

On an early 318, the fuel pump relay was black and about the size of the wiper relay in the fuse box.

On the later M42, this was the set in their full factory original glory (from left to right main, fuel pump, oxygen sensor heat):



Hope this helps at least somewhat,

RM

[ScottL]

Great Thanks. I know that the fuel relay is furthest left so that only leaves one big and one smaller relay. Would the main relay be the biggest one of the three?

Looking into the engine bay from the driver-side fender, my '87 was (left-to-right): main, fuel, O2 heat. The main relay was in a metal "can" and was the smallest, but that doesn't mean much. Relays are classed not by color or size, but by number of poles, contact configuration, solenoid voltage, and electrical current capacity.

As Jim said, no idea if that was where they were when the car was made, but I have no reason to think that they were moved.

[ascott430]

If it helps here is a picture of the group of 3 relays. The one on the top is the fuel pump relay.


IMG_1717 by ascott430, on Flickr