I believe that I am having the same problem.
I am trying to install a 2003 speedo into my
EC300 with 2002 wiring harness.
The sensor from the rear wheel has three wires
leading up to the steering head. One red, white
and blue wire. This connector fits the connector
for the old style round gage, but the new gage
has only two wires. Both black.
See the pictures below.
The first is of both speedos that I am trying to swap.
The second picture shows the three wire connector next to the
2 black wires.
The third is a little wider angel of the second.
I have tried pluging in the two black wires in all the possible combinations
I can think of with out success.
Any ideas what I may be doing wrong? Why the old style uses three wires?
Is one of them supposed to supply 12V to the sensor at the rear wheel?
One thing I did not mention. I purchased the harness from another member and
have not tried to hook up the old style speedo to see if "IT" works or not.
So maybe my problem is with the sensor.
Is there a test with an ohm meter to check the output of the sensor with
the wheel turning?
Any suggestions would be much appreciated.
Thanks, Jeff So-Cal.