Got the new switch in, comparing new to old, the old one had a little play in it but when I swapped in the new one same result. I hear the relay clicking. I'm really missing not being able to drive my Mustang but at least it died in my garage. I'm not sure what to do at this point. I'm going to check the fuse again to be sure but something tells me it's either my battery or a wiring issue between the relay and solenoid. At least the Optima has a warrany on it but I'll get it checked to be 100% sure.

 

When it fires right up, do the lights dim at all on the dash, does it seem a bit of a slower crank?

If the relay is clicking, then ya, it's wiring, battery, or the solenoid itself, since you've already checked the starter and relay. The couple of easy ones to do next would be to check the two main grounds, frame to battery on the passenger side shock tower, and especially the engine to negative terminal one near the starter. If the engine isn't getting a good ground, that would explain this. Check the starter main positive lead as well, since this the the sole thing electrically in the car that can not be fused. After that, may wish to replace the solenoid.

The service manual link provided will go through step by step of how to truly pinpoint it.

 

You need to check for power at the starter when this happens. Check all your grounds too. It's bound to be something simple. Have you tried a jumper wire to the starter solenoid? Do this at your own risk and be sure the car is in nuetral, set the parking break!

 

No dimming whatsoever nor does it crank, just clicks (relay) so I think you guys are on the money regarding what it could be. Time to crawl back under there because I don't think the solenoid is getting energized.

 

Boy I feel stupid but at least I can admit my mistake. The positive lead from the battery to the starter was loose. When I added the Optima, I "upgraded" the terminal clamps to Kicker chromed ones. Well, the set screw came loose. While I feel dumb for replacing everything I did at least the problem was something simple, not an ECU or something like that. Thanks for your help guys. If anything, I learned more about my car through this experience.

 

another 'upgrade' gone wrong

I was betting it was the connectors for the starter relay in the BEC
as my low speed cooling fan relay socket suffers from intermittent
operation.
The relay clicks but no 12V going out to the cooling fan...

My parking break is also acting up... go figure