i just replaced the battery and alternator on my car. on 1995 Lexus LS400

What's my next step? After replacement of both battery and alternator car did not run for more than 15 mins and now only starts and runs when I have my jump box connected to it.

Asked by for the 1995 Lexus LS400
there is a charging system problem; possibly a defective
alternator. this is common in the cheaper rebuilds. might
be a good idea to let someone check it for you.