I have a mercury grand marquis and today I put it into park when I was ready to go it would not go into gear from park position any advise

For safety purposes, you need to press the brake pedal for at least 5 seconds. If the problem persists, focus on the Automatic Transmission Gear Position Switch.

Even though this link is written for Hondas, it will give you basic insight into automatic transmission interlock systems:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-3.html#post258005

Are you saying that you could not move the shift lever or if after moving the lever it would not engage the selected gear?

Check if your brake lights are working. If you have a bad brake light switch, it won't release the shift lever to let you shift out of Park.

If you can move the shift lever, but the transmission isn't shifting into gear, the shift cable that connects the lever to the transmission has likely come off at one end.

I have same problem and just realized I have brake light out. Will fix it tomorrow and let you know if that fixes problem. Hope it does as its been driving me crazy thanks for advise :)

I have a 1995 nissan sentra that will not go into gear