Tach issues

[DesertClaw]

So i've got a 87, 535i. When I bought it initially the Tach in the original cluster was out, recently bought another updated 535i cluster and for a while the tach worked perfectly fine, recently though it started having issues. At first it would be out on first start up, but id just shimmy the cluster a bit and it would work again, But now has stopped all together. Ive since opened it up, and the board looks super clean, no burns or breaks. And it's got the dual Sanyo Lithiums which ive read are super long lasting. But after voltage testing them they're both reading around 2.79 volts vs 3.+ volts that they should be. I was wondering if these batteries would be considered no good? Ive got my old cluster, and another cluster from a different model that also happens to have the same Lithiums, and theyre reading around 3.1 Volts. I'm swapping around some parts to try to get it working, but Ive heard some people say the bad batteries could cause tach issues, and heard others say batteries have nothing to do with the tach. MPG is out too, and both fuses look fine. TIA

[Shawn D.]

Have you checked the continuity of the circuits from the connector thru the pins on the installed components?

I suggest using DeoxIT on the connections.

[Chimi-Changa]

And check the C101 connector ( I believe it is) in the glove box back left corner? Its a clear connector with a green, black and i think white wire in one end of it.

[DJM1986-5]

And check the C101 connector ( I believe it is) in the glove box back left corner? Its a clear connector with a green, black and i think white wire in one end of it.

I repaired that same issue on that 101 connector. Whoever put a radio in the customers car pulled or cut into that wire somewhere between the connector and the cluster. Ran a new wire and fixed the problem. IIRC it was the black wire.