PPPP error code multiple electrical problems
 

1990 525i with PPPP error code. Symptoms: erratic tachometer, fuel and temp gauges not working, rough idle, and, more recently, battery dies overnight.

May have been precipitated by other fault; intermittent power window and wiper failures tracked down to positive cable junction (loose connections) about a foot from the battery. Well intentioned mechanics did some trouble shooting under the back seat and possible inside the dash, behind the radio. (Not a factory radio, but radio has been in there a year without problems.) Mechanics' work may well be unrelated to present problem.

Noticed something in the Haynes repair manual about the SI board and batteries that may be pertinent.

Apologies if this has been addressed in a previous thread, I looked and couldn't find anything.

Thanks

a 1990 E34 cluster does not have batteries, that was on older cars like E30, E28 etc.
PPPP means there is no communication between the cluster chip and the OBC. Remove the cluster and check the pins at the back of the cluster.
What can happen is that the capacitors get old, and these can be replaced in the cluster, see here BMW E32 - Dash Capacitor Replacement

Intermittent power window and wiper faulure can be caused by a haircrack in the fusible link
and apparently your mechanics found it
BMW E34 Website

Also check the speed sensor on the final drive
BMW E34 Website

As for PPPP: solder in new capacitors in the cluster and see if that cures the problem, if not, maybe you ask in a forum specialized on E34 like

BimmerNut.com Forums
or bimmerforums or bimmerboard E34 section


As for the battery:
Max closed current for Z3 is 30mA