Start button short

[Ddarlington36]

It only happens after it been running awhile could be a short or loose fuse but it sounds like after a certain time the amp draw becomes to much to sustain..... Makes me now believe you have a weak ground because its fine on cold starts but after awhile its too much. Look on the frame body for the ground make sure its bare metal sand it down some if not. You could run a second ground if necessary sometimes the ground isn't thick enough gauge like if you have audio , LED lights alarm etc..