spinnin4th

[hr]
I just bought my 89 lx 5.0 with a few basic mods (full exhaust, clutch, 373s, msd ignition) and Ive been having some battery, starting issues. When I bought the car the previous owner said the battery was dead from sitting and after he charged it, it was starting and driving fine. I then noticed the more i drove, the harder it became to start until the other day i went to start it and after slowly cranking smoke began coming from the starter relay. I replaced the relay and it started fine after having to charge the battery again. I go to drive it the next day and the battery is completely dead. So i bought a new battery drove it fine for a little and the same increasingly harder to start issue happened again. Clearly something is draining the battery when the car is sitting idle, and it seems as if the Alternator is not recharging the battery enough because after driving for a bit, it wont start back up on its own power. Does anyone have any advice to help fix this..and if somethings drawing from the battery when the car is off, how do i find out what it is and fix it??? Thanks a lot!