2002 Venture Help needed

i installed a new alternator and bateery after the car wouldn't start after a trip. Every thing went dead but i could jump the van and it would start but not after turning the van off. after the install the van started 2x. now when i turn the key everything goes dead (it doesn't start and the interior lights goes off but once i turn the key back to take the key out the ignition the interior lights goes comes on. any ideals would be a help. also i almost forgot that when i turn the key back all the gauges start jumping and flickering (the speedometer, gas and temperature gauges).

tia