Electric Problem

[lexus for life]

I have a 98 LS400 when I put on the lights and come to a stop my radio goes off and the lights on the dash start to dim. When I start moving the radio comes on and everything is ok. I took it to the dealer and paid $89.00 for a diagnostic and they told me it could be the alternator, battery or termnals. This was just general and they too did not seem to know what was wrong. I changed the positive terminal since mine was not in good shape and it is still happening.

[SW03ES]

My guess is the alternator. I'd replace the battery at the same time since often a failing alternator will take the battery with it...