Need Help Wiring

phunk

The relay kits generally only address the power wire from the battery to the connector above the top hat. A Walbro 450 comes with its own wire pigtail pre-attached to the pump. Then there is an additional pigtail sold separately (but often included in vendor kits), that plugs into that first pig tail. This additional pigtail is what you will generally wire to the connector on the bottom side of your top hat. I have attached a picture to show what I mean. It displays the Walbro 450 with its integrated pigtail, and then an example of the additional pigtail you can purchase that plugs into the pump. This is everything you need for wiring between the pump and the bottom side of your top hat. You will most likely shorten that extra pigtail to be only a few inches long for this application.

Make sure to upgrade the pump ground wire above the top hat. You will probably have a section of larger wire from the relay kit left over that you cut off, and you can use this to ground the fuel pump to chassis. If the ground isnt equal to the power wire, upgrading the power wire doesn't really help you much.

For a twin pump.. you could theoretically wire both pumps to a single relay. This is assuming that relay is rated for the current of both the pumps combined, and assuming the battery lead for that relay is large enough for both pumps combined. The problem with this is that you will not have individual control of the pumps, and that is not ideal and not suggested. By having a separate relay for each pump, you can turn them on individually. This is called pump staging. You will ideally choose one pump to be the "primary" and this pumps relay should turn it on exactly as the stock relay would turn on the stock pump. You want it controlled by the original fuel pump circuit, so you use the original fuel pump wiring to activate your new larger relay for the primary pump. The secondary (or "auxiliary") pump should have its own relay that is activated just when you go into boost. This can be done using a Honeywell Hobbs pressure switch to close the relay activation circuit. Or in some cases you can use an ECU output programmed by your tuning software to do it, pending you have an available output and your tuner knows how to setup the software to do it. The purpose of pump staging is so that you are not idling and driving around town with 1200hp worth of fuel cycling your system. This would not only increase fuel temps and evaporative emissions, but it is actually a little difficult to regulate fuel pressure with such a high volume of unconsumed fuel to bypass from the system. It requires a very large regulator and return line, more so than off the shelf return fuel kits will come with.

I have attached a basic twin pump and twin relay wiring diagram. This diagram shows the most typical way people will wire twin pumps. I have done it this way, and I have changed it around some other ways. Once you become familiar with wiring relays you will realize there is a variety of ways you can do this. I will explain the small modification that I made from this diagram for the twin pump in my Mustang. So if you look at this diagram, there are 2 conditions that have to be met for the secondary pump to turn on. That is the original pump wiring needs to be activated, and the pressure switch needs to be activated. What I change for the second pump relay: I take terminal 86, and instead of connecting it to the original fuel pump wire just the same as the primary relay, I instead loop it right over to its own terminal 30 and splice it to the battery power. What this changes is that now the second relay only needs 1 condition to be met to activate, and that is closing pressure switch. The reason I like it that way, is because it allows me to do a very simple secondary fuel pump test. I can walk up to the car, pop the vacuum line for the pressure switch off the intake manifold, and blow into it to activate it (my switch is a 2psi switch, and that is already quite difficult to hit by blowing into it, so this wont work with higher pressure switches). So with the engine off, ignition off, fuel system off, I can blow into that hose and the secondary fuel pump lights up, I can clearly hear it without any background noise, and the fuel pressure gauge on the regulator flies up, and I just confirmed that my second pump and relay is working. This did actually save my *** once because the secondary fuel pump relay in my Mustang failed at some point, and I caught it with this exact test that I will do every so often before I drive it. Had I not caught it, I would have been running lean at full power until I just happened to look at the AF gauge and notice it, which may have been too late.

Attached Images

	DUALPUMPWIRING2.jpg (103.4 KB, 59 views)
	pigtail.jpg (313.7 KB, 29 views)

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