I ran into this on my old King Cobra years back when i went with a rear battery and a high torque starter...too many amps through a crappy circuit kills components as you are most definitely experiencing now. Heavier gauge leads is the way to go. Less resistance means more power with less strain. I run huge copper to my battery and the same from the solenoid to the starter as well as a ground to the alternator and to the frame. i recycled some 1 guage copper from a generator job and used copper crimp ends and soldered them and shrink tubed them as well as coating all the exposed connections in dielectric grease. I run a crappy Wallyworld Everstart 1000cca battery and i can run the starter for 45 seconds and the solenoid barely warms up...no exaggeration! Your ground(s) are vitally important for a high torque starter. The stock cables are ridiculously small for a big engine IMHO. Fine for a little Honda or a 4 banger but these engines need serious torque to get going in most cases.

 

Check your voltage drop at the starter when cranking. You have a 12 volt system. You need 10.5 volts to crank up with authority. If you are dropping 9.5 it won't crank with only worthless attempts. Look to the crimps on the wires if all is good elsewhere. Also the Relay/solenoid can get burnt contactors. Sometimes a no go at all ? If you have a amp meter around the cable it will register well over 100 amps available when cranking. Dist bad, engine will cut out and die probably.

 

Im running 00 gauge welding lead wires! There is no problems with the wire! lol.

 

If you clamped onto the leads with reusable clamps, check that area for corrosion you can't see without removing them. Blue green and no power flow/low amp flow thru em. Fine stranded cable vs heavy stranded cable?

 

do you have all the ground re-done and/or checked? Is the starter cable all the way down from the solenoid to the starter new?

 

Have you tried and replace your Ignition Coil? My old nissan for the life of the truck wouldn't start. All it did was spin over. I had to replace both Ignition coils and it started firing up first try each and every time.

 

DC power is reduced by the length of the cables. A voltage drop of lower than 10 volts will negate the dual battery due to distance. A many stranded cable ( much more expensive) will conduct much easier than a course stranded one. Find the voltage drop, you find the problem area. A clamp over the cable meter will help immediately to find the drop in current flow. It can simply be the contacts, ie, worn burned won't conduct power completely or not at all at times.

If you have a bad cell in one of the batteries it can rob the system of capability.

 

Theres not a bad cell in the battery. But i have not replaced the coil.

 

OK, you need hot spark to start. Same way a vacuum leak will kill ya.