Could be poor connector contact. Take off the connectors and if there's corrosion, spray some wd40 and burnish the corrosion away with the smooth shank of a drill bit. Take the connector apart (observe color codes so you can reassemble) and crimp the female pins for a better connection.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked