the Over Voltage Protection Relay, or OVP, is likely the issue.

I dont know where it is on your car, but my 85 has one and will disable those systems if it is broken.

dd

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'85 300D, 'Lance',250k, ... winter beater (100k on franken-Frybrid 3 Valve Kit)
'82 300D, 'Tex', 228k body / 170k engine ... summer car
'83 300TD Cali Wagon 210k, wife's car