Electrical issue

I've got a 2007 Taco 4wd with a 4.0. I'm having a weird issue. It won't turn over. Turn the key and it clicks like a dead battery. So I get someone to jump it off. I drive it home and it loses power for 1 second and keeps on trucking. It does it again ans the speedo needle drops and it goes back to normal. I get it home and start diagnosing it. I hook up the OBD2 and it shows no codes. I hook up the battery charger and charge it all night on trickle charge. It has 13.2 volts. I turn the key and nothing. Headlights are dim. So I get another hand to come over. He jumps it off and it runs rough at idle but when it gets to operating temp it smooths out and runs fine. I turn it off and it won't crank back up. Here's where it gets weird. I hold the volt meter on the battery while my buddy cranks it. As he gets in the truck, I mean sits down in the seat, the voltage starts fluctuating heavily. It goes from 13.2 down to 5. Up to 8 and back down to 5. He turns the key and it drops down to 1.2. He gets out of the truck and it reads 12.7. Wtf is going on here? Is it a bad connection somewhere? The alternator cable is tight. The battery ground is tight. When running its at cold and running rough it fluctuates between 14.2 and 14.7. When it smooths out its steady at 14.4. Any help is greatly appreciated.

 

Intermittent short in the wiring for the seat.

 

Start checking chassis grounds.

You could also have a bad cell in the battery. Load test at a parts house is free.

 

I would replace the battery. Start off basic before you go looking at wiring

 

Second this plus it's free .

 

You need to start by checking voltage drop from the battery negative post to the body and also to the engine and from the battery positive post to the main fuse box power wire, the alternator positive post, and the starter positive terminal. You should get less than 300mv on a voltmeter with one end connected to the battery post (not the cable) and the other to the point you are checking (this must be done when the problem is occuring).

 

You all did read the part about sitting in the seat?

 

Maybe try and start the engine without sitting in the seat and see what the voltage does.

 

Could be a lot of things. My son had an infinity that the wire for light on the visor wore bare and shorted to the bracket. They stupid thing would cause all kinds of problems. A repair shop found it and a piece of heat shrink solved it.

 

Make sure battery terminals are sparkling clean and tight. 2 items i would have the auto parts store load tested are the battery and starter.

 

Aftermarket amplifier wiring present ?

amp under the drivers seat by chance?