I used the el-cheapo unit from J.C. Whitney, about $30 on sale. The diy instructions from this site included relay wiring as the lock/unlock pulses from the remote were not compatable with the air pump (believe the polarity was different from what the remote unit put out). Also had to increase the length of the units output pulse. Also (again) had to run a wire from the unit to the factory alarm for the disarm function (it would arm by itself but not disarm). The unit and all wiring (except the disarm wire) was contained under the seat next to the vacuum pump (didn't use the light flash function). This worked for an 87 300E and an 86 190D.

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Hanno
'79 6.9 Sold (after 27 years)
'83 280SL, 5 spd.
'94 E320 Sdn. 5 spd conversion
'02 E320 Sdn.(on loan to mom!)
'87 300E (5 spd. conversion) Sold
'05 E500 Wagon