Hallo, folks.

It's cold out and I really don't want to pull my fuel sender out of my car. I think that there is a pinhole or kink in the in-tank pump on my 1990 740GL *Regina*, which now has 2 fuel pumps in the Bosch style 1 in tank, 1 under the car arrangement.

For the moment, I can turn the key to KP2 and let the fuel pump run for its normal 2 second prime, then repeat that until the fuel pump under the driver's seat makes the noise that tells me the air is purged from the system. It's rinky-dink and I would rather not do that, especially with an aging battery.

I have a bunch of spare EFI relays that need their solder fixed (it's cracked) and want to solder in a simple momentary switch to ground that will let me turn the key to KP2 and then hold the button down to run the pumps for 10 seconds. Can I simply solder a wire onto the EFI relay for 86/2 and then run it to a momentary switch that goes to ground on the other side of the switch?

The diagram would just be

EFI relay pin 86/2 --- ./. --- GND


If I do that, do I run any risk of hurting the ECU by flowing current from the "not grounded" circuit inside the ECU to my ground? Max run time would be about 10 seconds.

The FAQ talks in 2 sections about a bypass for bad pink-label -561 LH2.4 ECUs, but that's on an already-dead ECU. https://www.brickboard.com/FAQ/700-900/EngineFIComputer.htm#ECURelayGroundWorkaround

Happy Bricking!
Will