Information Warning Lights

1994 Deville 4.9
Every now and then the dash warning lights go nuts! Battery Voltage High - Anti Lock Brakes - Air Bag.........all of these lights flash. If it happens when I'm stopped and start to go the tranny seems to be in neutral momentarily then engages and goes. Also, the when this is happening the headlights seem to get brighter then normal. Had a new alternator installed. New battery. The only other thing that I can think of is the plug that goes in to the bottom of the alternator is not tight because the locking clip broke off so I wedged it tight with a small block of wood. Anybody got any ideas what could be causing this? Help!

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I had the same problem on my 1994 Deville 4.9. The problem was the battery sense wire that connects to the starter had a bad connection. So when the connection wasn't connecting right, the alternator goes to full charge and spiked the voltage to 15-16 volts!
I spliced in a new wire and connector to the starter wire, and have had no problems since. Also check for a broken front lower motor mount, which can aggrevate this problem.
There is a DIC modification to get the DIC to show the battery volts, coolant temp and engine RPMs. Let me know if you're like to know about that!

Thank you so very much for you reply and I will certainly check this.
Please send me the information for the DIC to show the temp, RPM and Volts.
Thanks again and GOD bless.

1994 Deville 4.9
The only other thing that I can think of is the plug that goes in to the bottom of the alternator is not tight because the locking clip broke off so I wedged it tight with a small block of wood.

You may have answered your own question. The computers want to see full voltage to operate correctly. In addition to what you noted, check the battery cables for integrity as well as all grounds.
FWIW
YMMV