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P-N-P switches, and some lessons learned. 900

posted by  The Zoo Keeper on  Mon Sep 6 17:12 CST 2004
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last visit: Fri Jun 27 08:34 CST 2008
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Well, after owning a 960 for about a year, my parents (mom) decided that a new PNP switch was in order since the trans light would flash in damp or cold weather (Minnesota). After reading the FAQ and many posts on this digest my father and I decided to obtain a new switch and replace the old one. We have learned many valuable lessons, and I will pass on what we have discovered.

1) If you live in the "salt belt", FORGET cleaning the switch. It will most likely break into a million pieces when you remove it. This also applies if you have a higher mileage or older car because the plastic sub-strait gets brittle. Basically, DO NOT attempt to remove the old switch unless you have a new one, or are SURE you can get it before you will need the car operational.

2) DO NOT purchase an aftermarket (Scan Tech) switch. Spend the extra $10-$10 and get an OE one.... trust me.

3) If you do not have GOOD jack-stands (not ramps) DO NOT even think about this.

4) There are a few "extra" steps in the FAQ that are not needed: The heatshields do NOT have to be touched, the oxygen sensor wires/clips do not have to be removed from the crossember, and you do not have to remove the return line (although it is easier to do so).

5) Based upon what I saw post-mortem, you can move the gear selector into "1" every time you get into the car and it won't help one bit. The contacts are not balls (like you would think and hope), but "knife" slides, and what happens is that the contacts on the switch arc (burn) and will not conduct properly. Moisture contamination is also a problem.

6) There are 4 larger (~14 ga) and 4 smaller (~18 ga) wires in the connector, of the larger, only the Red and Blue are functional, and they are the neutral safety wires. Blue/red in (engine harness side) is from the relay in the underhood fuse panel, blue out (both sides) is to the starter solenoid.

7) The switch really cannot be installed so the car will not start, the range of adjustment is too narrow. The adjustment really only affects the B/U lamps and signaling the gear selection to the TCM/ECM.

I have uploaded the photos I took during disassembly of the SWITCH so we can see what's inside. Notice the corrosion on two of the terminals in the connector.

In the photo of the slide contact diagram (I made), the sweep arm upper two contacts are the neutral safety contacts, the lower two pairs are GROUNDED thru the sweep arm (heavier line and ground symbol at piviot). Park is left and down (fully CCW), and "1" is up (fully CW).
--
JohnG 1989 245 MT @ 225,000








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    Additional information. 900

    uid 19's pic
    posted by  jbowers on  Wed Sep 8 09:00 CST 2004
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    last visit: Sun Jan 22 13:49 CST 2012
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    I just replaced the switch with an oem one on my car because the reverse light was intermittent and it wouldn't work while I was trying to get a Mass state inspection.

    On my '96 there was plenty of room to the exhaust so moving that or the associated heat shield was never an issue. My offset box end wrench had just the right angle to work the switch's mounting bolt. It had loctite on it so it had to be wrenched all the way out. (A long bolt!) I wire brushed the threads so my fingers were able to put it almost all the way in on re assembly. The big lock nut on the shaft coupler was left on after loosening, to use as a screw driver pry point for sliding the switch off the shaft.

    The transmission oil cooler return line disconnect was mandatory on my car. It would be a lot easier, with hind sight, if the clips tying the two cooler lines together were released and the end at the radiator were loosened. Have a small rubber stopper handy to plug the return line and reduce the drips of transmission fluid.

    The routing of the PNP wires on the '96 965 aren't anywhere near the O2 sensor wires so cutting ties there makes no sense. Mine were tied with the transmission temperature sensor and another ??? electrical device. They were the kind that could be released and reused. I was able to release all but one and reuse it. the last one I cut and replaced.

    I tried adjusting it according to the FAQ wherein the half way point of the back-up light on/off location was used. My light just stayed on for the entire adjustment so I just set it in the middle and everything's worked fine.

    With the car up on the highest setting of my jack stands, it took me about 2.5 hours including taking the cooler return line all the way off to smooth out some kinks and work some NeveSeize into the joints.
    --
    '96 965 with 16' wheels at 118K. Had '85 745 Turbo Diesel for 200K.








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      Additional information. 900

      uid 11021's pic
      posted by  dewfpo on  Wed Sep 8 15:27 CST 2004
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      last visit: Thu Oct 23 18:34 CST 2014
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      Wouldn't it have been a lot easier if they just mounted the PNP sensor on the opposite end of the shaft on other side of the transmission. All that room, no exhaust pipes, no cooler lines?

      DEWFPO
      --
      1998 S90 070,050 and 1995 964 153,010








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        Additional information. 900

        uid 19's pic
        posted by  jbowers on  Mon Sep 13 09:55 CST 2004
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        last visit: Sun Jan 22 13:49 CST 2012
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        And no heat from the exhaust to speed the degrading process!

        Maybe someone should design a bracket to do this. Then with the brack in hand, you could just add the bracket, put the new switch in place and switch electrical plugs. Leaving the old dead one to rot in piece.
        --
        '96 965 with 16' wheels at 119K. Had '85 745 Turbo Diesel for 200K.








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    P-N-P switches, and some lessons learned. 900

    uid 11021's pic
    posted by  dewfpo on  Tue Sep 7 06:29 CST 2004
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    last visit: Thu Oct 23 18:34 CST 2014
    [RELATED]

    What year 960 did you do this on?

    and

    How were you able to get the PNP sensor off without removing the ATF return line? (was the trans shaft so short that you could pull it off, then sideways past the return line?) The trans. shafts on both our 95 and 98 were so long that the the sensor would hit the trans line before it would clear the shaft.

    DEWFPO
    --
    1998 S90 070,050 and 1995 964 153,010







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