I was looking through the how-to's and information and never saw this mentioned anywhere, and it's actually applicable to anything with one of these.

If you're running high HP, you're using a lot of fuel. All of the power for the pumps comes through the intertia switch, and I found out the hard way just how those are built. They consist of a spring loaded copper plate, and when exposed to sufficient force the plate springs free and loses contact, shutting off the pump. That's the easy part - the tough part is those springs. They are considerably smaller than the spring in a ball point pen, and probably half the gauge thickness. That equates to very high resisistance at heavy loads, which causes a loss of power to the pumps and overheating the switch. In the S197 the fuse is a 5 amp, upgraded to 20 with the addition of a Boost-a-pump. With dual pumps the fuse requirement is 40 amps!

I bypassed this problem (after spending 2 full days searching for it) by installing a relay in the system while doing my GT500 pump upgrade. Mine was easier than most since my battery is in the trunk, but the premise involves running a large gauge wire (I used 10) to the relay which is then run to the pumps, or driver modules in the later years. The inertia switch is just used to activate the relay, therefore it still works to shut down fuel in an emergency. I present the following photos as an idea of what can be done and how to do it, but this is just my version.

I like to make use of factory connections, so I stopped by a boneyard and bought everything in this photo for $12.



I then start separating things to get the holders I want. For this application I need a relay, a 5 amp fuse and a 40 amp fuse. I pick out those holders, remove them and put them in a suitable container with epoxy. This is the cooling fan relay setup I built for my Ranger, using a box that included the nifty removable bracketry.



I like making my connections where they are out of the way, so I make them at the pins. They are double crimped: once on the wire and the second around the insulation. You will never open the one on the wire, so I open it at the insulation and bend the wire back and forth to create a stress fracture, breaking the wire off clean. I've tried this with a variety of wire cutters and they never work as well as the fracture. Use that crimp to hold on to the wire and then solder it. This joint ends up inside the connector seal, so you don't have to worry about heat shrink or weather. This photo shows a bare pin, then crimped and then soldered.



Finally, this is the configuaration and location I ended up with in the trunk.




Using this method to rewire pins I redid my engine compartment, doing all the connections at the PCM and fuse box. That was 25,000 miles ago with no problems.