This situation seems to be impossible, but it can't hurt to ask............

I put a front diff in my 2002 Tracker this week. Now I can't get the little pressure pump near the front bumper to run.

Read all about the flashing 4wd light so I think I understand how the stuff is supposed to work.

What has me puzzled is both of two pumps I have work great when putting 12V (directly from battery) on pins one and three.

That being done, I checked voltage at the connection to the pump (car side of plug). It reads 12.5 or 13 V.
But when I hook the pump up the voltage goes away! I've tried this 20 times with the two pumps I have, and it happens every time.

I know V=IR and some other electrical stuff, but don't see what can kill the voltage. I even jumped directly to the motor wires (skinned them a little) and the voltage from the car plug goes away.

Appreciate any ideas. Thanks, Gordon

Pins 1 & 3 - what color wires are we talking about here ?

The BLACK wire is connected to chassis ground and car supplies +12V on the RED wire - if that is where the voltage disappears from you have a bad (high impedance) connection.

Thanks for the quick reply. I read in some old posts to jump to pin 1 & 3; it even said "middle wire is black" but didn't say
to jump to it. These pins (1 &3) connect to red and pink (maybe orange).

If I jump the red and pinkish wire to +/- battery terminals, both of my pumps run well......so one of the colored wires must be involved in grounding somehow?

I thought I has a bad connection from the get-go. Both pumps run - so the plug on the pumps must be ok?

And I extended wires from the on-board plug. The red and pink wires always have about 13V between them until I touch them to the pump wires.

I'll try again tomorrow, working with black wire.

Really appreciate your help!

Gordon

Black wire is ground.
Red wire is +12V supply.
Pink wire is a sense or feedback signal to the 4WD controller.

With the pump air lines disconnected, the pump should run when power is connected between the red & black wires, and stop when the outlet is capped (for example with your finger) - if your pumps do this, they are probably (99% certain) in working order.

Very briefly, here is how it works - a switch on the transfer case is used to tell the 4WD controller, which may be part of the PCM (Powertrain Control Module) or may be stand alone, that 4WD has been selected, at which time the controller will supply +12V to the pump and then monitor the pink wire to determine when the freewheel mechanism has engaged, after which it turns on the 4WD light - if the controller does not see feedback within 10 seconds it will shut off power to the pump.

Fordem,

Thanks again. Hope I didn't blow up the PCM.

Will try again with right wires - don't understand what started all this! Didn't touch that system, that I know of

Gordon

Fordem,
'Bout ready to give this up, but one more question if you don't mind.
When I put a test light between red and black at the on board plug, and
 put the truck in 4wd, it lights. When I plug in the pump, nothing.

Could the pink wire be sensing something that causes the pcm shut off power?
Supposed to get 40 in snow over the weekend!

Hope they are wrong!

The controller looks for feedback on the pink wire and if it does not see it within 10 seconds of your selecting 4H or 4L, it will shut the power off - you will have to go back to 2H and then select 4H again.

Finally found a problem.Two of the pumps I have have a burnt copper path on the small circut board.

Pink wire no longer goes anywhere but thru the case.

Wonder if I did this while testing? I got aothr - afraid to plug it in!

TRied to attach photo; selected file but nothing happens

Gordon

First - you can try repairing those damaged pumps by soldering a scrap of wire across the burnt copper trace.

Second - it IS entirely possible that you caused that damage - you mention jumping the read & pink wires together - if you ever did that whilst the pump was connected to the controller and then shifted into 4H with the ignition on, the trace connected to the pink wire WILL burn, because you have shorted the power directly to ground.

Repair the pump and test using the instructions in my second post - with the test light connected between the pink wire & ground (black) - and when you cap the pump outlet and the pump stops, the test light should turn on.