Tach not working after replacing SI batteries...Any help.

[DerBayer]

Any info/help is much appreciated. Tach and MPG gauge not working on my 318IS. Read several threads, but hoping someone here can be of more specific help.
Replaced the SI batteries today, still nothing. However, SI lights came on and stayed on after ignition is off. A little later, green Lights kept flickering and then dissappearing completely. In addition to, OBC not working as well. With fuse 21 still in, OBC light has some power (weak red light), however no display visible. SI board looks ok and did check the Tach when cluster was out. Bad SI board, Wiring from Fuse 21 bad...or.??? Thanks in advance for helping me sovle this problem.

[richardodn]

Since the tach and mpg get their signals from the SI board, that indicates something screwed up. Was your board the lithium or NiCad battery type? Did you replace with the correct batteries?
OBC shouldn't be related to the SI board itself. Is it simply no backlight or are the display segments themselves dead?

[DerBayer]

Thanks for the reply richardodn...Its the lithium board and yes, i replace it with the correct 3v batteries. In addition, i made sure they worked before installation. In regards to the OBC, a very weak red light, no display visible however..Looks like not getting enough power! Was going to check the wiring from the C101 connector (black line) to the cluster connector soon. Massive pain all this suffice, but i love it

[dmw]

I have this exact issue. 1987 325i convertible. Tach and mpg gauge don’t work. Coolant gauge goes up to 1/4 even when warm. OBC lights either very dim or dark. I replaced the batteries (lithium). No change. Still doesn’t work. Any ideas? Thanks