Are you sure the RR34 unit will work with the Bosch alternator? This system needs a power feed through the charging light to energise the rotor through the slip rings.
In previous conversations on here, the RR45 unit has been used. Have a read of this thread…..
850 T4 not charging
Fitting instructions here from Gutsibits
https://www.gutsibits.co.uk/pr/TheShed/Downloads/BoschCombinedRegRecWiringInstructions.pdf