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Hey all,
doing an LS swap in one of my classics. A shop started the build for me but bailed and now I’m trying to retrace what all they did. I found some wires I’m unsure as to their intent, but they were mixed in with the fuel pump wire. Does anyone have a good wiring diagram for the fuel pump relays? I found the block, but it only has one relay. Pics below.
Ok used a schematic I found online. It requires ecu power on one terminal. Where do I pull that from?
also, it requires fuel pump +. Do I run that to the pump directly, or through the fuse block at the “fuel pump” fused location?
From: Jacksonville, FL (originally from Toronto Canada)
Why would you need two relays? The factory F-body configuration has a single fuel pump relay powered through the FUEL PUMP fuse and controlled by a signal from the PCM - basically the way your right side relay is wired.
Besides, your diagram makes no sense electrically - when the ignition is on, the left relay would merely connect 12V constant to existing ECM power, doing nothing. Unless you meant that pin 87 feeds power to the ECM when the ignition is on, in which case it's an ECM relay not a fuel pump relay (and still not necessary).
Why would you need two relays? The factory F-body configuration has a single fuel pump relay powered through the FUEL PUMP fuse and controlled by a signal from the PCM - basically the way your right side relay is wired.
Besides, your diagram makes no sense electrically - when the ignition is on, the left relay would merely connect 12V constant to existing ECM power, doing nothing. Unless you meant that pin 87 feeds power to the ECM when the ignition is on, in which case it's an ECM relay not a fuel pump relay (and still not necessary).
Thanks whitebird. I just found that diagram online, wasn’t sure it was correct. So I’m trying to figure that out.
so I delete the left relay and leave the right, but do I run my “pump +” through my fuse block? Right now my fuse block gives the “fuel pump” wire power when ignition is on. So I’d need to bypass that and put an inline fuse in the direct wire to the fuel pump?
From: Jacksonville, FL (originally from Toronto Canada)
Relays are nothing more than an electronic switch which controls one circuit based on another circuit rather than a physical toggle. This has many uses, but one of the most common is to control a high current circuit using a much lower current trigger circuit... such as powering a fuel pump based on the status of a trigger signal from the PCM.
The f-body factory system controls a constant (battery) fuel pump power supply based on a 12V low current fuel pump control signal from the PCM. There is actually no need for the supplied power to be constant as long as it's available while the ignition is on as well as when the engine is cranking. If your fuse block meets those criteria then there is no reason to bypass that in favor of a constant power feed.
Basically, you need to connect the following relay terminals:
30: power supply - either ignition+cranking or constant as you see fit.
87: output power to fuel pump.
86: fuel pump enable signal from ECM/PCM. (12v positive)
85: chassis ground.
In most cases, it doesn't matter if 86 and 85 get reversed, but on many newer relays there is a diode across those terminals designed to extend the life of the relay and those newer relays require positive on 86 and ground on 85, so it's always a good idea to do it that way even with older relays.
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Fuel pump relay 
