87 2.9 Ranger fuel pump

[253Kyle]

Fuel pump isn't turning on when key is turned on. The relay clicks but I'm not getting power to the pump. I tested the wires that goes to the pump under the drivers seat and its getting .002 volts when turned to on position and .95 volts when turned over. Relay (which is brand new) is getting 12.15 volts.

 

[RonD]

In passenger footwell in the cab just around carpet line there is the Inertia switch, it has a heavy weight inside that will move if vehicle stops quickly or rolls over, i.e. an accident, this inertia switch passes the power to the fuel pumps.

Google: Ford Ranger inertia switch images

So you can see what you are looking for, it can also be behind the passenger side kick panel.

It has a Reset button on the top, but once "tripped" an inertia switch can never fully reset, so best to replace these if it has been "tripped".

You know the fuel pump circuit only runs for 2 seconds when key is first turned on, then won't have power again until engine RPMs are above 400.
You can test for 12volts at each terminal on the inertia switch but turn key on and off and on again.

Fuel pump power runs this way
Battery-------Fuel pump fuse----------Fuel pump relay--------inertia switch-------Fuel pumps

1987 could use a 30amp fuse for fuel pump power or a Fusible link.
This power comes from battery directly usually hooked up to the Starter Relay on the fender where battery "+" cable hooks up.

The Fuel Pump relay does NOT use this power, it PASSES this power, so the fact the Green Base fuel pump relay clicks doesn't mean this fuse or fusible link is OK.

If you pull out the fuel pump relay and with Key OFF, test each slot in the green relay base you should find 1 slot with 12volts, that's power from the fuse or fusible link, so that part is OK, if no 12volts is found then fuse or fusible link is blown

 

[253Kyle]

So I found the problem. It was the inertia switch wire. It fried. Almost couldn't even get the plug out it was melted. Can I just bypass that switch and put a fuseable link in its place?

 

[RonD]

You should replace it, but can by-pass it.

No, a fuse or fusible link wouldn't help or be required, point of the inertia switch is to prevent fuel pump from continuing to pump out fuel in the event of an accident.
It could be there is a short in the wire that caused the melting or a fuel pump is drawing too many amps, and when you by-pass it, it may blow the 30amp fuel pump fuse in engine bay.

Computer will shut off fuel pump(via fuel pump relay) if engine RPMs drop below 400, so inertia switch is a backup system.
In an accident or roll over, assuming a fuel line breaks, the engine would stall because of lack of fuel, unless the Return fuel line was the only broken line, and if engine stayed running fuel would keep pumping out, which could cause a fire.

So up to you really, at temporary bypass should be fine but I would replace inertia switch.