Fuel pump relays

[viven44]

I know you don't target anyone... if anything I thought you 'spared' me

I think it is very important to hold the high standard y'all have built up here. I know people come here because Facebook can get 'noisy'.

[ArdWrknTrk]

I'm sorry folks. There was a bit of a palaver out in the street.
Cops were called on me because the jac-off across the way came a hair's breadth from getting a good taste of the steel toe of my work boot.  😡

I'll get into it if you like, but for now let me open the EVTM images in tabs and compose a way to accomplish testing with the continuity/ohms portion of a DMM.....
(again, it's going to take me a bit, but I promise I won't dismember anybody in the interim. )

[viven44]

Dang!!

Might I suggest pulling the switch out of the dash and checking for connectivity with a multimeter.

You should measure less than 1 ohm on all these connections

When the switch is in the front position
- pin 2 is connected to pin 1
- pin 5 is connected to pin 3

when the switch is in the rear position
- pin 2 is connected to pin 4
- pin 5 is connected to pin 6

[ArdWrknTrk]

Okay, the dash switch sends power to the switch valve, which moves the contacts inside and switches the senders.
I assume you want to know why the switch won't move the valve to 'front', correct?
Seems Vivek already got to the switch pin out....

If you ask the right question, I can give you the correct answer.  💡

You'll notice a rectifier (pair of diodes) in the rear tank feedback loop driving the valve's motor, which selects the senders.



Trouble shooting is at the end of each chapter. (I'll include that... for example) and the ground locations/illustrations are at the front of the book.




Now, the pumps.

[Jcomeau85]

Trying to troubleshoot why I can’t switch to the rear tank.  The front works fine.

[ArdWrknTrk]

With earlier systems rear was default and the mid-ship was only selected with power applied.
This "Hot Fuel Handling" version uses a switch valve that is driven either way, but remains stable state until the power & ground are reversed.

Let me look at the schematic and try to explain the troubleshooting at the back, in terms you can understand.

[ArdWrknTrk]

On the valve ground pin 2 and apply power to 1.
This should drive the bi-stable valve to the rear tank.

If you want to test the switch do like Viven said and see where 12V comes out when you flip the switch with the plug backprobed.