Did you buy the correct bulbs for the car? If they have a brass base they are most likely NOT the correct bulbs. The correct ones will typicaly have a silver base. The brass based US spec bulbs can have differnt current ratings than the European spec bulbs despite sharing the same socket footprint. The brass based bulbs can cause problems with the blinker, bulb warning, and cruise control. Making sure you have the right bulbs is the first step. A good test is to swap bulbs with the right side and see in the problem follows or stays with the left side.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff