The MDI box has three large harnesses exiting the box: an engine
harness, a control harness running to the start/stop panel, and a “multi link” harness running to the instruments or the instrument panel. This “multilink” harness carries power, ground and the instrument can bus data wires.
As you know it’s not a good idea to modify/cut any of the wiring
in the engine harness, as this most likely will interfere with the engine operation or the engine alarm
system. As an aside, the engine doesn’t have an oil
pressure sender, but it does have an oil pressure switch to drive the oil alarm
, and the oil pressure switch wire color is white/blue. The purple wire in the engine harness is used to energize the stop solenoid and stop the engine.
There is an accessory harness and relay which is available from VP to do just what you want to do, ie. drive items such as the fuel pump
. This relay harness is connected into the multilink harness, either at the engine end or at the instrument end of the harness. When the button panel is turned on, the relay in the harness energizes and powers up whatever accessory is connected to it. The relay is controlled by the engine electrical system
, but isolates the engine from whatever is controlled by the relay.
The part number for this relay harness is (was) 3594745. I’m not sure if this number is still current
so you will have to check with a local dealer.