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Discussion Starter #1
Hi guys,

I purchased a Ford Focus Sedan last August. After purchase I decided to tackle the engine light on constant. 4 things were referenced. When I replaced the top OS2 sensor and plugged it in, I noticed a wire dangling. Upon inspection and following the harness, I noticed the harness and wiring was chewed through and teeth marks on the wires.

I repaired all, but 2 wires. My dilemma is with the Power Steering Pressure unit. The mice or kittens (it's more pleasant thinking it was kittens.) were kind enough to not eat matching coded wires on all but the Power Steering unit.

The unit has only one coded wire B/Y, going in and out of the unit. I purchased a manual, and it shows they both go to the PCM, one is negative and the other is marked PSP switch. I am assuming this is not like an ordinary house current that just makes a loop, so it would not matter which wire is spliced to which.

So I need your expertise on duplicate wires. Is there an instrument that I can test which wire is spice to which wire? Or is there a simple way to tell which wire to connect to which on the other side without blowing up the PCM?

Can a simple light tool tell me which is ground and which is positive switch, like light in the handle and an alligator clip plugged into the handle? If so what do I have to be careful about when troubleshooting?
 

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AFAIK, the PSP switch is a passive on-off mechanical switch and therefore wiring orientation does not matter, hence why the color coding is the same on both wires. If you want to test for the polarity of the supply terminals on the PCM without the use of a multimeter, try using an LED instead. The anode (the side with the notch) is your positive.
 

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Discussion Starter #3
Confused, there is no power on the switch side for both wires. Will only one wire on the PCM side have power? Have a Multimeter, but not powerful enough for a car battery.
 

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You will need the switch connected to both PCM wires to be able to see any voltage across the switch terminals. The switch itself does not provide any power - it's simply a push-to-make switch activated via a pressure diaphragm. I also think that the engine needs to be running or the key has to be in the Start position at a minimum so it can wake up the PCM.

As for the multimeter, surely it can measure at least 15VDC. You're probably referring to the current which I understand as most conventional meters cannot read more than 10ADC. For your purposes however, you need a voltage reading. Set it to something around 20VDC and measure across the wiring coming out of the PCM. If you get a negative reading (or the needle goes to the left if your meter is analogue), swap the probes to match the polarity.
 

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Hook up either way should be just fine, as mentioned it's just an on-off switch.

Don't need it for much, senses excess pressure (usually when steering is held to the end of it's travel) so the PCM can bump the throttle a bit to keep idle speed steady (parking lot maneuvers).
 

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Discussion Starter #7
Sailor, thanks for your info, I thought as much in the back of my mind, but needed to know for sure. Better safe then sorry and creating more work for myself. Thanks for your knowledge sharing.
 

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Lora83, if I could figure out how to upload a picture on this site, I would could show you that the teeth marks resemble those of a kitten. Kittens have been known to live in engines and survive.
 

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Ferrets are also keen on eating rubber and foam. I had one parking himself in the engine compartment in Winter and dining on the soundproofing !

If you want to upload images, select Go Advanced beneath the Message window and choose the paperclip symbol from the toolbar.
 

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Rats have front teeth easily as big as a cat's...........................a cat may jaw with a wire but they generally don't damage their teeth by going all the way through. Rats, though............wiring is a tooth sharpener to them. Gotta keep 'em sharp for the cats.
 
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