SPEEDOMETER

1988 BMW 735

Tiny

Ralph735

August, 19, 2010 AT 2:23 PM

Electrical problem
1988 BMW 735 6 cyl Two Wheel Drive Automatic 189K miles

my classic 735i runs great and is in exc. Condition, well-cared for with no engine problems, but the speedometer/digital odometer and cruise control just failed last week after a 200 mile mountain drive. I did some downshifting into 3 and 2. The tranny is smooth and perfect. I do not abuse the car.

i think it may be a relay switch but there is no diagram on the inside of the fuse box. Do you know which relay is the one to replace, if any? They are expensive and I do not want to just throw new parts at it. I may be able to get an entire fuse box with relays from a salvage yard cheap and start replacing the relays one at a time till something good happens.

all the fuses are fine.

Ralph

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Tiny

bluelightnin6

August, 19, 2010 AT 2:26 PM

The speedometer receives signals from a rotating magnetic disc mounted on the rear axle. It is most likely faulty. It needs to be checked with an ohmmeter. Ohmmeter should receive pulsating readings. This also gives information off to the on-board computer, cruise control and service interval circuits.

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