speed sensor wire
Moderator: martauto
my speedo only works when it feels like....
ive changed the sensor in the diff and checked the wiring from there to the conection block under the rear seat. does any one know where it goes from there and what colour is the wire at the speedo side and how to test for a signal???? thanks... bjdp 
- Longman325Touring
- E30 Zone Newbie

- Posts: 200
- Joined: Sun Sep 27, 2009 11:00 pm
You say you've 'checked' the wiring from the sensor - have you actually replaced it.
Over time the wire becomes brittle and will break within it's sleaving, so externally there is no visable damage. 99% of speedo woes can be fixed by simply replacing the connection plug and about 20/30 cm of the wiring.
Over time the wire becomes brittle and will break within it's sleaving, so externally there is no visable damage. 99% of speedo woes can be fixed by simply replacing the connection plug and about 20/30 cm of the wiring.
i put a seperate wire from : i by passed the junction block under the rear seat just in case it was that connection (soldier two wires by tapping into the original sensor wires) and took it down to the conction on the rear diff. i didnt change the connection plug i cut the old wire off and soldier the new wire onto the original one.... maybe i'll try a new plug...thanks guys
- Brianmoooore
- E30 Zone Team Member

- Posts: 49359
- Joined: Mon Jan 10, 2005 11:00 pm
In that case, turn your attention to the speedometer in the cluster. Dry (cracked) solder joints have been known to occur on the speedo circuit board near where the pins that plu into the main board are fitted.
The sensor in the diff. is a simple reed switch, so a meter switched to 'ohms' will show alternately zero resistance and infinite resistance as the rear wheels are rotated.
The sensor in the diff. is a simple reed switch, so a meter switched to 'ohms' will show alternately zero resistance and infinite resistance as the rear wheels are rotated.

