Checking wiring for speed and reference sensors

[shogunther]

Is there a way to check the wiring harness for the speed and reference sensors? I replaced both sensors, gapped them, and the tach does not bounce. I was looking at the plug diagram from clark's and I did a continuity test on the sensor plug to the dme plug. Funny thing is the wires on my sensor plugs seem to be mixed up. For example: terminal 8 and 23 are switched(on the sensor plug side) and terminals 25 and 78 are switched the same. Can someone verify that clarks is accurate?

[mikepellegrini]

The view of the speed and ref sensor plugs on Clark's is straight out of the Porsche shop manual.

Here's a copy of the wiring diagram from an 86. I'm not sure, but I'm guessing they're all the same. Wire color codes: SW = Black, WS = White, RT = Red, GN = Green, GE = Yellow, GR = Grey, BR = Brown, BL = Blue, LI = Violet.

I'm guessing the grey wire on both is shielding (as in shielded coax - pins 78 and 23) and probably should always be to ground [easy to check]; the black and yellow wires actually operate the sensors.

The correct sensor must be in the correct plug; if you plug the speed sensor into the reference sensor plug, you won't have a tach bounce (or anything else - ask me how I know). Is this maybe what you have going on?

[jasonmx5]

So is it safe to say that one way to tell the speed sensor and refernce sensors appart on the harness side would be to look at the middle wire going to the connector?

If middle = Black then Reference Mark Sensor
If middle = Grey then Speed Mark Sensor

Could it be that simple?

[mikepellegrini]

Yeah, I guess in theory. But you'd almost have to pull apart the connector to see. Although the pin-out diagram in your first post doesn't show it that way.

I tried to find a wiring diagram of the actual plug but was unable. There is no pin "78" on the DME, so I'm not sure where precisely they get that. The wiring diagram shows DME pin 5 as the third pin on the reference sensor plug - not 78. 5 and 23 are both grounds (I believe).

There is a yellow band on mine - says "DG" for the speed sensor and "BG" for the reference sensor. You don't have those on yours? May only be on the sensor end - I couldn't see much of the harness side on mine.

Rather than pulling back the insulation on the plug and seeing which wire is where, I'd just try plugging them into the other sockets and see if it runs that way. Easier...

[jasonmx5]

Originally Posted by mikepellegrini

There is a yellow band on mine - says "DG" for the speed sensor and "BG" for the reference sensor. You don't have those on yours? May only be on the sensor end - I couldn't see much of the harness side on mine.

Rather than pulling back the insulation on the plug and seeing which wire is where, I'd just try plugging them into the other sockets and see if it runs that way. Easier...

True enough, I was just figuring that their might be some easy way for folks like me who's little yellow bands have gone the way of the dodo.