I'm at work right now so I don't have my '88 TEWD and TSRM with me. You need to find out the wire colors for IG1 (Black/White) and IG2 (Black/Orange) and test those for continuity with the switch turned and with it just in the "ON" position. IG2 is the main suspect. Both should show 12v when tested against ground.
MK3 TEWD On-Line