The Big 4 has 3 grounds battery to engine, engine to frame , and battery to body. That is why your getting voltage drops .you have ground resistance.

 

Do as you have done..piggy-back the 0 gauge POS cable from the Alt to Batt and leave the original in place. The small one carries signals to the PCM for the Alt output. I did mine the same way a few years ago and has been flawless since. No extra cables are needed at the starter itself as the starter grounds through the engine block. As for the low output, I would suspect a battery on the way out..the Motorcraft batteries of the last 4-5 years are NOT what they used to be. If the battery is low or going bad the Alt will show a low volt and high amp output as opposed to a good battery the alt will normally show 14+ volts but with a low amp output. I did mine according to this How-To :https://www.f150online.com/forums/ar...c-heavy-2.html using the photo on post # 19

 

This batt is not that old, the factory motocraft went out the door a while ago, this one i have now is from advanced auto. Now i dont remember seeing an engine to frame ground. I gotta look for that.

 

That cable goes from the Neg to the R Front spring tower mount. When done their are three cables connected at that point. I'm not saying the Alt is ok..it might need testing, but you can't rule out the Batt either if it was mfg. by Johnson Controls. Sorry..read the post wrong. The cable you are looking for goes from the Serp. belt tensioner to the spring tower (the three point area, one being the original small ground). On mine the original ground cable is completely disconnected from the battery and taped up .

 

The third ground, engine to frame is from the belt tensioner to the spring tower(where the other bround is)?

 

And what would be a good battery? I hear the yellow top optimas are not what they use to be. Say if i was to get a h.o alternator, do i have to change the pulleys? Im not that educated on the pulley setup.

 

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