How to check voltage incoming in the inertia switch

[fabianoliver]

Hello all, 94 manual XLT
I need to check if 12V is arriving at inertia switch.
How can i check it?
+ probe at green cable at switch, and ground to chassis?
thanks for your help!

If 12V are arriving at inertia switch and i bypass it, there's another connector in the fuel pump line bringing voltage to the fuel pump prior to the fuel tank in one side of the chassis?
Where it's located?
Thanks for your help!!!

 

[410Fortune]

It goes like this
Battery to fuse to fuel pump relay fuel pump relay to inertia switch inertia switch out to pump

The pcm controls the fuel pump relay

Yes you have it correct
With test light or multimeter you are looking for battery power at intertia switch inertia switch
But it will only be there when the fuel pump relay is triggered by the pcm, so for 1-2
Seconds when you first turn the key and then full time when the engine starts

You can check for power at the relay and then bypass the pcm trigger to send power to the fuel pump yourself

Now this is from memory I do not have the wiring diagrams for a gen 1 in front of me right now…
But basically that is how it works

 

[410Fortune]

Found this right here on Ef this is for a 94 explorer

 

[fabianoliver]

Perfect 410! Thanks for your reply.
3 questions more by now:
1: How can I bypass the pump relay with a jumper? Just to check if the relay is working..do I jumper the 30 with the 87 pin at the relay connector?
2: I’ve a multimeter, so I assume all chassis is ground right?
3: if I have voltage in the relay, and not in the inertia switch , to make a bridge and go straight to the inertia switch from the relay do I take 12V from the 87 pin?

Thanks!!

 

[Josh P]

1. Yes jumper 30 to 87
2. Yes
3. Yes. If you do have power on the green wire but not on the pink with black stripe, jumper those two to bypass the inertia switch, then check for power at the fuel pump connector.

 

[410Fortune]

Boom

 

[fabianoliver]

1. Yes jumper 30 to 87
2. Yes
3. Yes. If you do have power on the green wire but not on the pink with black stripe, jumper those two to bypass the inertia switch, then check for power at the fuel pump connector.

Txs Josh!
Last one ( until tomorrow...jajaj)

how is the path ( 94 XLT 4x4) of the cables from to relay to the inertia switch, and from the inertia switch to the pump?
I mean to check if i have any short, and to try to find it if i have...

I'm in a strange situation.
My truck suddenly died a few days ago, and I brought a pump from the USA to Uruguay. Since my job meant I had to leave the city, I left the truck at the mecanic where he took it to get the pump swap.
The mechanic told me the original pump was working, but when they put in the new one, it burned out, and then the original one burned out too when they replaced it, and that they were having a hard time finding the short circuit ( bad praxis and diagnosis IMHO) He finally put in a Bosch one, and it started working, but the day after I brought it home, it wouldn't start. When I called it to tell him, he said I should take it back for a check, but I'd lost trust in him.
I'll have time tomorrow and after tomorrow, and I hope to find the solution and where the error is.
I want to trust in my truck, i need it stable, i use it for work.
Thanks for the advice!

 

[fabianoliver]

Ok, just made some checks:
No voltage at inertia switch Just 6.9 V ( pcm?), so I connected 12V from battery to pink cable in the inertia switch connector, pump runs, truck starts.
So straight to relay box:
Pump relay connector only shows 12V at pin 86 when key in on position. No voltage on pin 30
20 amp fuse is ok.
20 amp fuse connector shows 12V in it's left pin ( looking truck at the front) when key on.
I don't know if i should have, but i don't have continuity from right pin 20 amp fuse connector to pin 30 in relay ( cable 175)

Can i assume i have a bad 175 wire between 20 amp fuse and pin 30 on pump relay?

what's the best way to take of the relay connector from the distribution box? just to rewire and take a look?
How can i continue my research?
txs all!!

 

[410Fortune]

Pin 85 at relay red
should have battery + when the key is turned to run
This is acc power from the eec relay

Pin 30
Black with yellow
Should always have battery power +
This is power constant direct from
Fuse 22

Pin 87a at the relay
is power OUTPUT. to inertia switch and fuel pump (dark green w yellow)
Battery + Power is only available when the key is first turned to run and the pcm primes the pump or when the engine turns over and the pcm sees a signal from the crank sensor that the engine is turning.. then the pump runs whole time engine is turning

Pin 86
Is fuel pump enable light Blue with orange
This is a ground relay trigger, - negative
Fuel pump Monitor
This is the wire that the pcm uses to connect the relay to ground, thus turning on and off your fuel pump

 

[fabianoliver]

Pin 85 at relay red
should have battery + when the key is turned to run
This is acc power from the eec relay

Pin 30
Black with yellow
Should always have battery power +
This is power constant direct from
Fuse 22

Pin 87a at the relay
is power OUTPUT. to inertia switch and fuel pump (dark green w yellow)
Battery + Power is only available when the key is first turned to run and the pcm primes the pump or when the engine turns over and the pcm sees a signal from the crank sensor that the engine is turning.. then the pump runs whole time engine is turning

Pin 86
Is fuel pump enable light Blue with orange
This is a ground relay trigger, - negative
Fuel pump Monitor
This is the wire that the pcm uses to connect the relay to ground, thus turning on and off your fuel pump

Thanks a lot 410 for your help, and time.
Well problem solved, by now. Hope it's stays on.

The Mistakes i've made in diagnosis:
The fuse 22 in my distribution box is empty, WHY?....
The only 20amp fuse ihad was the 19 and it was healthy, so i assumed this 20amp fuse was the pump one, error.
In the distribution box, i've seen a 25amp fuse blown, position 18, i thought it was related to the climate fan that it's hesitating..., and NO
I replace this broken fuse by a 20 amp one ( marked 20 on the cover box), i cheched the car with key on position, and i heard the pump running. Bingo. Now the pump is working.

So, someone changed cables routing from the distribution box? mistery.

My last question is: someone changed the fuse to a 25amp, and after 2 years of running with me, it blows.
What can be the causes that blows the fuel pump fuse? a tired fuel pump?

Thanks a lor for your help.

Marked on the picture where the 22 is suposed to be, and where the 18 is.