This is my first posting ever.
Infiniti I30 2001 90,000 mi. Florida car with no visible rust.
Owned it in Wisconsin for 2 years.
Car always started great. A month ago I turned the key and it cranked for half a second and then nothing. Next several turns of the key and nothing. I found the cable leading to the starter solenoid loose and with green corrosion. Cleaned it, put some electric grease and perfection. One solid month of no problems.
I am now having an intermittent cranking problem. I can turn the key and get a perfect start. If I try a again I might get nothing.
No crank no solenoid click, nothing. I have a good tested battery. I have started it in neutral and in park. It has also failed to start in neutral and in park. I replaced the starter relay near the radiator at the beginning of the problems. Both the old and the new starter relay appear to be good. Not sure where to look next or what my testing procedure should be. Taking it to a mechanic is out of the question. I have a multimeter and a very basic idea of how to use it. I can perform almost any mechanical task with the right guidance. Help!

Could be a bad ground.

Or just a bad starter by now. If there was corrosion on the connector, there very well could be corrosion inside the starter as well.

Thank you darylzero. You assume I know where and how to test ground. LOL Where are the pertinent starting system ground locations and how do I test them?

Rather than jump from idea to idea, can we please go through a full ignition system check from key to engine turning over?

The battery is good, fuel supply is good. The car will simply turn or not turn over randomly. It makes no starter or solenoid sound when it fails to start. But then it might start perfectly. Again the problem is intermittent.

Moved to Maxima / I30 / I35 Forum.

This might prove useful: 2001 Infiniti I30 Factory Service Manual

Update: I used multimeter and I had no voltage on the wire to the starter solenoid. I turned the ignition key to on, attached a jumper wire between battery positive and the solenoid pigtail and the car starts.
From what I understand the systems and controls between the key and the starter solenoid pigtail are:
the ignition key cylinder,
park/neutral position relay,
selector lever in the P or N position,
ground on the P or N lever in the P or N position,
park neutral position switch

Can anyone intelligently guide me through locations and procedures to check these in order?

The jump test from batt to starter assures that the starter is good. Check the condition of the + cable from batt to starter that could be bad.

You note all the places to look and when I have issues I use the shop manual to guide and fix.

There are also harness to engine grounds that could be corroded -----> shop manual to locate

Could have safety start and alarm system issues, need to be checked ------> shop manual for details

One possible the park gear selector switch could have a intermittent contact and this directly effects starting and no start if no contact. To check when you have a no start condition when cranking and no start in park jiggle the gear selector and see if there is an intermittent contact, these safety switches go bad.

You have already done the start relay so OK there.

I had intermittent start issues with my 98 I30 and even though the starter worked most times there was intermittent conditions where it didn't or lazy. Replaced the starter and all well. All other systems were ok.