When I turn key I get intermittent response from starter. Sometimes nothing, other times barley cranks. Rebuilt starter from bruce. New battery jumping posts with key on or off only spins starter motor. Bad starter?

Start with the basics… is the transmission ground strap connected and giving a good ground?

Yes. I checked grounds

Jump the solenoid not just the starter. Does that work?

I’m jumping the two posts

Battery good and charged? I assume if you got it from Bruce the starter was checked and is good… sounds like a power or solenoid issue. Is the supply positive good and connection is good?

I’ve been jumping wrong part on starter. Should be positive lead to spade terminal. Now starter engages. I will test voltage of switch at starter. Pretty sure it’s a bad switch

It could just be the normal "time to put a Ford solenoid on there". The original is picky about 12v. Google it. I will be heading for the door before the purists get here....

IMHO, running a relay is a good idea regardless.

There's really no need to run all that current through the starter switch.

Ya’ gotta laugh how the solution is always to add weight to a 914

That Ford part probably adds at least 5 HP...

How?

You cannot tell the quality of a ground cable just by visual inspection.

The most reliable way to verify a ground cable is measure the voltage drop across the cable while simultaneously cranking.

This is because you’re trying to measure less than 1 ohm of resistance which many cheap o’ multimeters will struggle to do.

Good reading regarding how to measure and judge acceptable voltage drop across a ground.

https://www.fenderbender.com/running-a-shop...ircuits-part-11

The most misunderstood aspect of the stater is that it typically draws 50-100 amps of current while cranking. This is in addition to the 25 amps of current that the Bosch starter solenoid needs to draw to pull in and operate the actual motor correctly.

It only takes a minute amount of resistance in the ground cable to cause HUGE problems due to the high current draw.

As an example .01 ohms of resistance in a ground cable will drop 1.25 volts (way too much) if drawing 125 amps of current while cranking.