BMW E30 weak low beams or tail lights not working
Why are the E30 low beams weak?
The most common cause is an old sealed beam whose reflector surface has darkened or flaked; a new sealed beam improves the light output the most. Another cause is oxidised old connectors and wires that waste voltage. Good-quality bulbs also help.
How do I find and fix the electrical faults behind weak low beams?
Measure the voltage drops: the drop across a single component should not exceed 0.2 V. A drop that is too large means the wires, relays or connectors must be repaired. An oxidised connector and a piece of wire are replaced with new ones, and the wiring often breaks near the lamp connection. Thicker wires or relay control can be used to help.
Why do the E30 tail lights not work even though the bulbs have been replaced?
Check fuse 22: if it blows, both tail lights and the parking lights go out. Otherwise the fault is often in the tail light's plastic connector or the wires, which become brittle or come loose, and the connector's contact surfaces may be worn.