I have 7 spare used MFTS senders that came from parts cars and/or junkyards for free or $1 each. Five are the 4 pin units, and two are the 3 pin units. Is there any reliable to test to see if they are good before installation, and is the 4 pin unit better on a 20v200 as I saw mentioned somewhere? I would prefer to not spend $60 for a new sender to just have it fail in a year, BTDT before! Cheers, Brian