On my 300TD, it is the other way around. There is a ground location on the right side. I cleaned the terminal and sanded the body where it screws in. Made a difference but the left is sitll brighter.

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96 Legacy LSi wagon
92 Mitsu Expo
95 525iT
1983 300TD clackclackclack sold
1972 Toyota Corolla wagon TE28 sold
1991 Galant VR4 pshhhhh non-op
1989 Montero RS pop's ride