MSefi.com read only forum (Jan.15,2018)

I found a 12V 3PST relay and nice socket at the local electronics shop. A single run/crank 12V signal energizes the relay, and three separate circuits get completed for the fuel pump, injectors and the LC1 02 wide band. The MSII also gets power from this signal.

Simple question; can this run/crank 12V all be sunk back to pin #37 on the MSII (as the fuel pump one does in the diagram) rather than having the LCI trigger and FI triggers go straight to ground and only have the Fuel Pump ground through #37? The current is no greater...it would only mean that any "control" that #37 provides would be applied to the Fuel Injectors and the LC1 the same as it is for the Fuel Pump, right? Any problem with that fact?

Thanks. If this isn't a problem, it makes for a nice clean wiring setup for me.

I think I answered my own question.......... NO

Even though getting 12V upon crank (and a confirmed good coil in the relay), when grounded through pin #37 exclusively it doesn't complete the circuit upon crank. #37 must need MSII to be live for it to go to ground. Since MSII is powered by the result of this relay along with the fuel pump, LS1 and injector bank, I have circular logic. I don't think it is a good idea to put MSII power on the crank circuit, right?

Spittybug wrote:I found a 12V 3PST relay and nice socket at the local electronics shop. A single run/crank 12V signal energizes the relay, and three separate circuits get completed for the fuel pump, injectors and the LC1 02 wide band. The MSII also gets power from this signal.

It's normal to have a second relay for the pump - you don't want it running all the time the ignition is on. Only when the engine is running.

Simple question; can this run/crank 12V all be sunk back to pin #37 on the MSII (as the fuel pump one does in the diagram) rather than having the LCI trigger and FI triggers go straight to ground and only have the Fuel Pump ground through #37? The current is no greater...it would only mean that any "control" that #37 provides would be applied to the Fuel Injectors and the LC1 the same as it is for the Fuel Pump, right? Any problem with that fact?

Thanks. If this isn't a problem, it makes for a nice clean wiring setup for me.[/quote]

The fuel pump mustn't ground through the MS - must use a relay.

I can't really see one odd relay is going to look better than two standard ones. I've used a twin output type as the main relay - saves a connection or two. One output feeds the MS and Tech Edge wideband, the other the injectors.