My son has a short (i think) in his car and maybe you guys can help me here. When he leaves the car sit overnight the battery will be dead most time. This means there is a draw of some kind and how would i check this out. Is there a piece of equipment i can use or do you folks know something i don't. The car is a clean 1987 mercury grand marquis 5.0 (big boat)

 

I had a 90 F150 with the 5.0. It had the same problem. It turned out to be a stuck relay fot the eec 4. Every time the fuel pressure would drop the pump would kick on. As long as I drove it every day it was ok. When I left it for 2 days it was dead.

Disconnect the neg lead on the battery and put a test lite or amp meter in series. If it lites up you have a drain. pull fuses until it goes out.

When I went to the dealer to buy a new relay the guy says it is a high fail item.

 

FIRST CHECK AND CLEAN THE BATTERY TERMINALS THEN CHECK AND MAKE SURE THAT THE CABLE GOING TO THE STARTER ARE NOT MELTED TO THE HEADERS AND LAST MAKE SURE THE NUTS ARE TIGHTLY HOLDING THE CABLES TO THE STARTER