Hi,these Rangers are legendary for dubious,recalcitrant electrics...
Your new units are confusing the ECU,and will be reading the lack of load,as a fault.
Check if the replacements have resistors paralleled with the lamps,which you could add,but not straight forward...
The ECU needs a letter writing to it,for every change/addition.on these,and i had a fraught episode of multiple visits,to the local dealer,who fitted a towbar and electrics to me pals new Ranger,that they supplied. The electrics never functioned,and they defaulted to colourful stories,which ground to a stuttering halt,when fronted in person...
Upshot,was a mid mounted ECU fault,£400+ which was a warranty cost,they tried massively to evade.