I have a 1988 Ford F-150 XLT lariat 2wd. I recently put in brand new tanks, new fuel sending unit pumps, new fuel pump, new selector fuel tank pump, and a new fuel filter. Also changed out the 15 amp fuel from the fuse box to a bypass fuel holder since the one I had was completely melted out. As I go to crank the truck the pump isn’t making a noise. I go to the fuel injectors and press the button and gas shoots out. I start the truck it turns but dies out, go back to the button gas is no longer pumping through. I went out and bought a light tester and the fuel pump has no power in the wires.(keep in mind I had to cut the old wires from the old pump to connect them to the new one) the inertia switch had power in the red line, but the black line has no power. In the relay under the hood the green relay has a short in two of the connectors but fully bright in the other two. The brown has full power in all three except for one. I don’t k ow to much about wiring at all to give you some more detail, but I’m pretty sure if you all give me some info I can figure it out. ReLly need some help here it acts as if it wants to crank but it’s not pretty frustrating cause the hook up on the tanks were self explanatory; if it’s tight it’s right on the sending units right,
​​​​​​​

 

Posted in the other thread, but I'll add it here for giggles.

I could be wrong, but the power found on only one wire of the inertial switch sounds like an issue. The switch would normally be closed and allow the power to pass through it. Having none on one branch sounds like either the switch is tripped, or faulty.
Have you tried setting and resetting it a couple of times and testing again? Might be worth the trouble to do while you're waiting for someone that actually knows about the system.

And on our trucks, I believe that the inertia cut-off switch is in-line with the power from the relay to the pump. Rather than in the control circuit for the relay. At least that's what someone said a couple of weeks ago while I was listening.

Regarding the readings you got at the relays, how are you testing? With relays inserted and back-probing the connectors? Or with them removed and probing their connectors directly?
Generally speaking (very generally, as Ford may have a variation on this theme) you should only see 12v at one or two positions on the relay when the circuit is off. Depending on whether the relay is switched with ground or 12v positive. If ground switched, you'll also see 12v on a second terminal.
I think the relay on our trucks is ground-switched from the ECM directly. So 12v power to two of the connectors, ground to one, and switchable ground to the fourth. Then power out to the pump.
You should be able to jump one to another and have the pump run. Since yours is an '88 you should be able to to the test with the jumper wire in the two ports of the data terminal.
Did you try that already?

And you really should buy or borrow a fuel pressure gauge to attach to the schrader valve. You can have fuel squirt out at a fairly decent pace and still not be enough to run. You need to see in the 40's as far as psi goes I think. But even just 10psi is enough to squirt fuel pretty good out of the valve.
So it's hard to tell for sure what you are working with by just the eyeball method.

Good luck. Hopefully one of the others chimes in with good intel for you.
Hmm, just had a thought... In '88 were they still using one of the feed-back carburetor setups? Or whatever the interim components were, between carb and EFI?
Or had they gone to full port injection by that time?
Shows how fickle the memory can be!

Oh, and something I did not add in the other thread was that "just because it's new, don't make it good" phrase that we all run into these days. So your pumps can be faulty and all that. But because you're getting strange readings at the wiring, we'll stick with that for now. Just wanted to bring up the subject.

Paul

 

The fuel pump relay is energized for 1-2 seconds whenever you cycle the key from the Off to Run position. After that initial 1-2 second delay power to the fuel pump is removed.

To keep the fuel pump relay energized jumper Pins 2 & 6 on the self test connector then turn the Key to the Run position.

Attachment 277274
courtesy of Subford

Attachment 277275
courtesy of Subford

 

I’m checking the relays while they are unplugged. Where would I put the jumper wire to see if I can jump off the pump? I’m not to fond on the numbering of the relays also so I wouldn’t know where the 2&6 would be located.

I’m testing my inertia switch while it’s unplugged. Should I plug it in and reset then check the wiring? If so where would I plug in the test light to see if its getting power?

Here’s the pump. The pump has a black wire swinging from out of it pretty sure that’s the ground wire if I’m not mistaken. In both my wires on my pump I didn’t get any power going to them according to the test light. Should I try to jump it off or is that a clear sign that it doesn’t work. Keep in mind I had the inertia switch unplugged while hooking the test light to the wires. If that doesn’t matter how would I jump off the pump? By connecting jumper wires to a ground a hot wire?


Here’s a closer pic of the relays under the hood I’m testing those unplugged also

 

You need to connect everything back up. From there you can use your test lamp.

On your 1988 model year truck the self test connector is probably part of this relay/connector assembly:



Attachment 278420
courtesy of Subford

 

What Randy said. Sometimes those connectors are cleverly hidden (sometimes even in plain sight!) but they're such an odd shape and size that you should be able to find it if it's still there.
Once you find it, whether it's got the cover on it or not, the pictures posted above clearly show how to jumper the two connections.

Good luck with the search.

Paul

 

should I buy a multimeter and probing tube just in case

 

A DVM (multimeter) is a handy testing tool. No idea what a probing tube is.

 

yo check out the new post I just posted

 

So i ran the test on the brown and tan wire. As I connected the alligator clip to the positive terminal the light came on and stayed on. As I cranked the green light flickered but still stayed on, and then went back to normal as I stopped cranking it. Also my starter didn’t kick out due to not enough battery power would this cause a problem?

I ran the next test which was to connect a ground wire and a red probe to the brown wire. As I did this I probed the wire and it read .04 volts DC. As I went to crank the highest it read was .50 volts DC. Keep in mind the started didn’t kick out; would that cause a problem? Or is that not a big deal

 

check out the new post I posted just in case the other guy doesn’t view

 

Ok so I changed the relays because they were bad. As I turn the key over I still here no wining noise from my pump to let me know it’s activated. The inertia switch is every wire has power, but the pump still isn’t activating. I have electric pumps inside the tank you think that could be a problem also should I unhook the ones in the tank and just run the pump on the wall? Or do I need to change the pump out?

 

Are you sure there is power going into and out of the inertia switch? How did you test it?

 

I tested the inertia switch by getting jumper wires and plugging them into the two ports on the inertia switch. I turn the key over still no hmm from when I hot wired it.

I also traced the brown wire that comes out of the inertia switch to the top. But there were two brown wires one showed bright green and the other was a dim light.




I traced the wires from the fuel pump back up to the top and hooked a 12v light up to the positive battery terminal and it shined bright green on both wires even when plugged in and wired up to the line it connects to. So the fuel pump is getting power.

 

If you have verified power is getting to the pumps then you need to follow the path to ground.