Wiring Fuel Pump Relay to Alternator

[carrera205]

I'm installing an electric fuel pump on a 1991 Mercruiser 5.7. The wiring harness for this boat has almost no keyed power options so I've connected the excite wire to the keyed power on the back of the alternator. Everything seems to function great but I've seen some people say not to do this. Would love some feedback here.

 

[Scott Danforth]

use a blocking diode if you are going to take power from the excite wire.

 

[carrera205]

Thanks for the reply @Scott Danforth some explanation would be great.

 

[alldodge]

The excite wire to ALT is also the + side to the coil

Use the Yel/Red going to the slave relay, and can use either from key or going to starter

Use these to circuits to feed the oil pressure switch and no need for ALT wire unless you want to take it off that location

 

[flashback]

I pulled power from the + on the coil, it was close to the relay. No problem yet. My goal was to keep the wiring simple and compact.

 

[carrera205]

I pulled power from the + on the coil, it was close to the relay. No problem yet. My goal was to keep the wiring simple and compact.

I tried doing that pulling it from the ignition coil and after the engine was running there wasn't enough power to trip the relay so the fuel pump would stop running. For now it seems the wire connected to the alternator is working well just wasn't sure if there was a safety issue.