I'm something of a ticket expert, and also live in San Diego. On that note, ANY comment from any other state is completely irrelevant. Almost all moving violations deal with state law and any other state isn't worth considering even the most compelling of anecdotes.
The city of San Diego does NOT operate red light cameras anymore, but surrounding cities do. Encinitas recently voted to not renew its camera program with the vendor, but I don't know if they're still operating. Solana Beach and Del mar still have active red light camera programs. Those are the ONLY cities in the county that have(had) camera programs this year.
Your ticket is ONLY valid if it indicates a local Superior Court on it (Kearny Mesa, most likely, potentially Vista - depending on where the intersection was).
Frequently what the red light companies will do is send you a 'snitch' ticket, where they try to get you to tell on someone for the violation. These can be IGNORED. Only if your ticket involves a CA superior court on it is it valid. It will have a citation/case number that you can look up on the Superior Court's website.
If you do have a superior court listed, DO NOT IGNORE the ticket. I'd recommend doing what's known as a Trial By Declaration (contest ticket by mail). There, you should argue certain things if they apply:
'The ticket does not clearly indicate the identity of the driver. Red Light tickets are issued to the registered owner, but citations can only be delivered to vehicle operators, and the police have the duty to prove the identity of the driver beyond a reasonable doubt'
'The ticket arrived later than the required time from incident to notice' - Check if the date of the violation is more than 11 days from the postmark - it might be invalid
CA Veh Code § 23
The giving of notice by personal delivery is complete upon delivery of a copy of the notice to the person to be notified. The giving of notice by mail is complete upon the expiration of four days after deposit of the notice in the mail, except that in the case of a notice informing any person of an offense against him under Section 40001, the notice is complete 10 days after mailing."
There are more options, but FIRST THING. Determine if you have a REAL ticket, issued by a Superior Court. Anything else is garbage, throw it away.