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Main Relay (archive)

[ Follow Ups ] [ 7-series (E32) Message Board ] [ Msg. Board FAQ ]

Posted by gale on January 02, 2001 at 13:49:15:

In Reply to: Re: Battery Problem posted by Max Fretter (NZ) on January 02, 2001 at 11:59:55:

The main relay is in the "E-Box", located in the corner by the firewall on the pass. side (right). The cover comes off with 4 Phillips screws. In mine, it's the white one (orange one is for fuel pump). I pulled it out & took the outer cover off. Points look clean but if they're burned, there's a small diode at the base of the solenoid coil that clamps the inductive kick when the points open that could cause the points to arc if the diode is bad.

The e28 board has frequent mention of the main relay or "mustard relay" (cause it's yellow?) which gives many fits.

To all that have replied so far:

Search the archives for the Russian URL to the Mitchell Inc schematics for the 735. Check for "main relay" or "load reducing relay" or something like that - I can't remember the exact term used. The one I'm familiar with is "load shedding relay" - these relays are set up to isolate/power-down whole subsystems (lights, HVAC, radios, sensitive electonics) during starting (1) to protect them and often more (2) to give the engine electronics the highest possible battery voltage (most of them don't care about current too much, but don't like voltage sag)...

Main point (sorry I'm a little long-winded today) is to find the relay and try swapping it with something else - your call on dirty contacts could be right.

Max F
87 735i
86 K100RS (2)

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