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I just found this hanging down and I noticed that it has the same color wires as the ones that go into the back of the cluster for the speedo. I'm hoping that's my problem. I changed the sensor in the diff and no dice, so I figured it might be a disconnected wire.

The ETM will show you exactly where that plug goes and its use.













That is the electrical connector for the interior temp sensor

I'm highly doubtful that plugs in anywhere in the back of the cluster. I haven't had my cluster out in a while, but at most, you should have the two L shaped connectors that connect to the "blau" and "weiss" spots on the back of the speedo that bring in the signal from the diff. Other than that, all you have are the three large connectors, one white, one blue and one yellow (ecu, obc and something else...). Try to trace where it is coming from. I know that every e28 I've seen has several connectors all over the car that aren't plugged into anything. My theory is that they're connectors for euro-only options that could have been had on the cars at the time.

Blue Shadow wrote:That is the electrical connector for the interior temp sensor

bingo, I completely forgot about that one. I was mentally going through trying to remember all the connections under there. FAIL.

duggi wrote:I'm highly doubtful that plugs in anywhere in the back of the cluster.

I knew it didn't go to the back of the cluster, but I was hoping it would connect to the other wires that go to the back of the cluster. I figured I wouldn't be that lucky, though. I've always heard of the etm, but I don't know where to get it. Anyone got a link?

look at my sig

Does your OBC work? If so, do you get any speed readout when you reset the average speed? If so, the problem is the speedo. If not, it may be the mother board or SI board.

mooseheadm5 wrote:Does your OBC work? If so, do you get any speed readout when you reset the average speed? If so, the problem is the speedo. If not, it may be the mother board or SI board.

OBC, cruise, funometer, or the odo (gears are good). I've tried 3 clusters and no change in anything.

tsmall07 wrote: OBC, cruise, funometer, or the odo (gears are good).

So none of these things work or they all work?

mooseheadm5 wrote:

tsmall07 wrote: OBC, cruise, funometer, or the odo (gears are good).

So none of these things work or they all work?

Sorry... none work.

I replaced the sensor on the diff with a used one that I don't know was good. I figured it was unlikely for both to be bad. Anyone know what kind of reading I should get if I put a multimeter across the connectors on the sensor?

THe sensor is actually a magnetic reed switch that pulses the ground open and closed as the blades of the tone ring in the diff pass through it. If you hook a multimeter up to it set to ohms you should get alternating open and closed circuit readings as you turn the wheels (off the ground, car in neutral.) If the sensor passes, you need to check the wiring harness from front to rear. You can use a spool of copper wire to make really long leads for your multimeter.

So I guess there aren't any other components between the diff sensor and the speedo?

Check the wiring diagrams.

duggi wrote: but at most, you should have the two L shaped connectors that connect to the "blau" and "weiss" spots on the back of the speedo that bring in the signal from the diff. Other than that, all you have are the three large connectors, one white, one blue and one yellow (ecu, obc and something else...).

Autotragics have a wire connector that goes onto the "gear selected light board", or something like that, .
Anyway, it's the little panel with the lights that tell you what gear you're in.

I second checking the wiring under the car. An exhaust leak pointed at the wiring can disintegrate the wire. This happened on my 528e. 2 feet of lamp cord and some watertight connections fixed it all up nicely. Follow it from the diff as far forward as you can see. It'll be fairly obvious if there a section missing.

Jeremy

I have the same hanging plug in my car. It is an auto to 5 speed swap.

Is it the interior temp sensor? (i noticed my car blows some heat out the top when everything is closed)

tschultz wrote:I have the same hanging plug in my car. It is an auto to 5 speed swap.

Is it the interior temp sensor? (i noticed my car blows some heat out the top when everything is closed)

Might want to fire up a new post about these two issues, but yes, the connector is the interior temp sensor that is located at the left front corner of the under steering wheel cover. Your stuff there may be gone so nothing to connect to or it may not have been put back when the swap was done.

With everything off and getting a nice blast of warm air can a hole in the floor/firewall or maybe your car has the fancy electrical fresh air vent control ('86 on) that can come unattached or fail open. This would put air into the fresh air vents, the dash vents.