SI board power - ignition or always hot?

[BigD]

The cluster in my swap has been sitting for a while, and the car sits mostly with the batt disconnected. My tach is not working. I was told that the batteries in the cluster, if not dead, can recharge.

My question is, do I need to drive the car for this to happen or just plug the battery in and leave it for a few days? (this is not as dumb as it seems, considering the fact that this is a track-only project...)

[AlarmedBread]

I'm not sure, but I removed the batteries from my SI board (vdo cluster) and everything aside from the econometer and SI lights works perfectly. This is acceptable because I replaced the mpg gauge with a different one.

[BigD]

Hrm... perhaps when you wired in the new gauge you also provided power to the plug reader/tach?

Does anyone know for sure?

[jlevie]

The cluster is fed with switched and un-switched power. The latter is to keep the NiCads in early SI boards charged and to prevent running down the Li cells in later SI boards. I don't know which you have, but if original it would be NiCads and they may well not ever come back after being drained.

[BigD]

Perfect, thank you! My cluster is a VDO from an 88 or 89 M3. Hopefully by leaving the batt attached it'll come back...