IDW what the V should be during cranking ? If I can get to mine this afternoon I will check . 40 % loss sounds too much ? Also check V drop between components . Starter to battery ground , then battery to starter solenoid ( both sides of the solenoid too ) . When yo see a difference in V , narrow it down and repair . I fixed my buddy's SnapOn truck with a test light doing this . He had a no-start condition and crazy things going on . Turned out being ground problems during cranking . We put - straps w/shakeproof washers at the battery to frame , frame to gusset then frame to starter - , then to some other "stuff" up there ?