I personally love mine. The basic test is.... does the 4-M light illuminate with the key on and go out once started? Otherwise the main check is to pull the plug out of the side of the t-case and see if there is excessive fluid inside. If you pass both these tests you have a winner.

The function is that if wheel slip is detected it will send power to the front wheels. If slip continues it will then lock the rear differential. Any time the system is active it should light the triangle light in the center of the speedo.

FWIW, I managed to chirp a front wheel recently, the smile lasted at least half an hour.

__________________

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