Which wire is the "switched" wire for Main relay and where is it switched from?

[Jon K]

1992 525i M50, I am making some new relays. I want to trigger a new relay in the same manner as the stock main relay (i think) but I I want the relay to turn off instantly with the ignition.

[Javier]

by the DME when DME receives Ignition switch power.

So if I understand your question, the answer would be: Main relay is switched by DME, trough the coil ground (brown wire).

For what you want, there is a paradox, it is either in the same manner as the stock main relay, or it is switched (then turned off instantly) by the ignition switch.

In any case, I doubt there is an important delay switching trough DME.

Javier

[Jon K]

The DME apparently keeps the main relay powered 3 seconds after ignition shut off.

So there is an ignition wire to the DME? Do you know what wire that might be? Bentley is @ shop.

[Javier]

Ignition wire to DME is a green one, hot in run and start, the same that goes to power the ignition coils, it arrives to DME pin 56.

Javier

[Javier]

may be C221 is set to hold power to Main relay for a wile after ignition turn off.

Javier

[Jon K]

Javier it must be because I have my MegaSquirt ecu and GM coil pack coming off the main relay, I turn the car off after running it and remove the key - the car continues to run for about 4 seconds or so, its so bizzare. I want to make my own relay based on ignition switch but didn't want to run the wire. So, does that make sense? DME Pin 56 to a seperate relay - that should start and stop the relay with the key right?

[Javier]

Relay Coil + to pin 56 (or the green wire originally going to the coils), the Relay Coil - permanently to ground.

But you may loose some functions of the main relay. Guess there are some other conditions to turn it off no mater the status of the ignition key.

I would better wire the green wire (or pin 56) to Coil +, and main relay signal from DME pin 27 to Relay Coil -, that way Ignition key will immediately turn off the relay, and DME will also turn off following its own criteria.

Doesn't the MS have a Main relay operation output? if so you can still use that output to drive the relay ground instead of DME pin 27, keeping relay power from the ignition switch (green wire)

Javier

Edit: In DME systems, coils are not fed by the main relay but the ignition key.

[Jon K]

Relay Coil + to pin 56 (or the green wire originally going to the coils), the Relay Coil - permanently to ground.

But you may loose some functions of the main relay. Guess there are some other conditions to turn it off no mater the status of the ignition key.

I would better wire the green wire (or pin 56) to Coil +, and main relay signal from DME pin 27 to Relay Coil -, that way Ignition key will immediately turn off the relay, and DME will also turn off following its own criteria.

Doesn't the MS have a Main relay operation output? if so you can still use that output to drive the relay ground instead of DME pin 27, keeping relay power from the ignition switch (green wire)

Javier

Edit: In DME systems, coils are not fed by the main relay but the ignition key.

MS is reverse, the MS does not control anything other than the fuel pump relay by grounding that, the MS relies on a "main relay" to power it on, but since I used my "main relay" off the stock ecu to power the MS, the MS isn't powering off immediately when I pull the key out, so what happens is the engine runs for a bit with the key removed, its very odd.

[Javier]

isn't it cutting off with the ignition key?

You can just replace the red wire going to the main relay pin 86, with a tap from the green wire going to DME 56. This will cut power to the main relay when key off.

Javier

[Jon K]

That is true I could do that, that actually may be simpler!

I have the feed for the coils coming off the main relay... I am not running the OEM coils.

So, if I t-tap pin 56 to DME cut off the 86 pin on Main relay, solder 56 to 86, everythign should shut down with the key off