A bad cruise amp that possibly might need to be re-soldered. Mine will do that too. I know its the amp because before I replaced it, it wouldn't work at all. The new one works about half of the time.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo