E30 Cluster issues

[WYZEUP]

Hey Guys,

So during my time after my engine swap i noticed a parasitic drain which i traced back to my RPM gauge staying active after i had switched the car off.
So i decided to try and replace the batteries, being a chump i over heated the board and burnt it out.
Bough a new parts cluster, production date of 2 vehicles is 5 months apart, same cluster, si board looks identical only part i notice is different is it doesn't have the switch to turn the batteries off while its sitting.

Now my problem is swapping over the si board my tach no long works, if i swap my burnt out board back in the tach works....im lost at the moment if its a compatibility issue if the main board is different or if i need to swap tach's and things around.

Realy frustrating as the parts seem identical. Would flat si batteries stop the tach from working?

Any help would be great so i can sort this.

Vehicle is a 1990 facelift plastic bumper - produced 12/89 - cluster came from a 05/90 model

[superj]

I never had a board with a switch to turn the batteries off. that is new to me. the tach not working is super weird though. do they have the same coding plug?

[WYZEUP]

The later model ones had a switch to disconnect the batteries so they didn't go flat while sitting on the shelf. Same coding plug in both clusters swap them over when trying the clusters.

its got my stumped why the tach wouldn't work with the new board, but works with the old board.
Same clusters, only differences in the gauges are the fuel gauge and econometer are different on the cluster the board came out of.

[superj]

swap them over and see if everything works