all right guys here is my small contribution, I have just finished installing a vdo speedo in a customer's 97 d90.
the power up of the unit is described all over the forum, so is the conversion from mechanical to electronic speedo
on pre 96 "digital display odometer" trucks.
discission about the installation on 96 and 97 trucks however is very vague so I decided to make notes on my experience and here they are, if I can I will post a picture.
for starters, the factory plug at the back of the factory unit is a straight fit into the VDO unit.
the wire position do not match the location required by VDO in its instructions.
on the factory plug.
position # 1 is red with white tracer, this is lighted power (lights on/off)
position # 2 is white with green tracer, this is switched power (key on/off)
position # 3 is black this is ground
position # 4 is black with red tracer, this is the speedo PULSE signal (7 pulses per one wheel revolution)
position # 5 is black this is ground
position # 6 is empty, thus not used
position # 7 is yellow with pink tracer this is engine rpm signal to abs ecu, not used
position # 8 is empty.
on the VDO unit,
position # 8 is the speedo pulse signal input, black with red from factory position 4
position # 4 is the main power, it uses the white and green tracer from factory position 2
position # 7 is the main ground, it used any ground from factory position 6 or 3
position # 3 is the signal ground, with out this the speedo gauge will tend to act erratically. I did a "y" split for a set of grounds as factory provides 2 VDO needs 3, one for the lights.
the lights were wired in tandem and since they are fully insulated the power and ground can be reversed.
once all was installed, the VDO speedo would not register mph and I traveled a mile for it to register 1/10 of a mile.
a call to Egauges.com tech line solved the issue partially by suggesting the "calibration procedure" .
this issue was solved by using a gps to track a measured mile.
the truck was equipped with 4 brand new bf goodrich 265/75/16, the VDO unit provides a total count of pulses per mile... it turned out to be 8510 pulses per mile.
once it registered auto calibration, the speedo gauge begun to read and so did the odometer, within the gps readings.
BTW the factory speedo was replaced because it died, the odo stopped displaying.
I made short jumper wires in order to route signals as needed, and keeping the capacity of returning the truck to use the factory speedo if so desired in the future.
picture is last, showing back of unit with jumper wires ready for installation.
------ Follow up post added November 30th, 2011 09:03 PM ------