Speedo Not Working 628csi

Dear All

I am trying to figure out how to get the speedo working (assuming it isn't simply broken!) on my 1984 628csi .  It may also have been disconnected some time in the car's murky past but I have have been unable to locate any points where this may have been done.

Any pointers in the right direction would be greatly appreciated.

Thanks

Bob T

- yours being an E28 based car (unless its was registered very very late), it should have an electronic speedo, running from fuse F12. If this fuse goes out, then both the radio and a lot of the other instruments stop working. The ground connection from the speedo is common with the direction indicator repeaters, so if these work, the ground connection is OK. The sender is connected to the instrument cluster on pins 8 (gnd, Br) and 12 (signal, Br-Red).

This leaves the speedo itself, or as suggested above, the speedo sender.

I don't know hpw to check the speedo itself; I would say that the sender is ten times more likely to fail than the speedo. 

However, my understanding is that the senders on the hubs (if fitted) are just for the ABS system. The sender for the speedo I understand to be on the Diff housing, and it should be easy to find as it is the only electrical gizmo fitted to this part of the car.

 One of the two wires should run to ground at the dash, the other won't. If so, the wiring at least is probably OK.

 Use a high quality digital multimeter for these tests, or get someone who knows what they are doing to do them for you. Don't under any circumstances use a test bulb; you could do damage. If the tests above check out, you at least have good wiring.

I don't have test data for the sender itself, but if they are like others I have dealt with, it will measure a few hundred ohms if it is OK, and it will be open circuit if it is past its sell-by date.

I hope this is of help to you  

cheers

 

I have exactly the same problem with my E28-635CSi.  The speedo didn't work when I collected the car from being in storage for 2 yrs.  Have looked thru the service history and all componants relating to the speedo were replaced 3 months before the previous owner died and the car was stored.  I am hoping that the cause is just lack of use.  The fuses etc all seem to be intact but shall be investigating underneath the car when she goes for MOT.