I had same issue. Was starter. Replaced it and no more trouble for ME. Expensive and not easiest job. Preform test I mentioned earlier as well as look at wave form pattern. Waveform pattern takes a scope. Not everyone has one. Volt drop test can be done with volt/ohm meter. Don't try amp test on starter without shunt or vat40 or something able to handle the high amp a starter requires.

 

Do you know the amp draw spec? I haven't heard of someone refer to a shunt in years lol, right on

 

On cold start mine was drawing 460A peak, measured with Fluke scopemeter and current clamp.
I think nominal current is rated at 100A.

 

You need at least 80 sustained amps @~12V to turn the car over, or just under .6kW of power any less and that starter is going to struggle. The alternator/generator outputs up to 105 amps.

 

for those that did the relocation,you wired starter directly to battery?