1991 745T

Sometimes, when the key is at position II, only the seatbelt light is on. Sometimes, check engine, oil pressure, ABS, seat belt, shift arrow light are on. When this happens, there is no voltage on the skinny little post on the back of the alternator, and there is no charge to the battery (measures lower than13V). Sometimes, when the key is at position II, all the dash lights come on, and in such cases, the battery posts measure 14.3V and of course there is also 14.3V at the little post. Is this the definite sign of the electrical part of the switch going out? For now, I have to hot wire the little post to the battery to make sure the battery is charged. If I need to leave the car sit for more than 2 hours, I disconnect that temporary wire. Want to check with you guys before order the $100 little electrical part. Thanks. Erwin