Hello, this is my first post here and I am in dire need of help. I have a 1999 Mercury Cougar and I can not get it to start after letting it sit for a few hours. It will only start after you disconnect and reconnect the battery. As soon as you do that, the car will start right up and you can power cycle it over and over again but let it sit for a few hours and it won’t start. I’ve charged the battery numerous times, it shows 12.5 v and I can hear the fuel pump whir to life as soon as I turn the key but I wouldn’t hear the starter if the car has been sitting for a few hours. I have googled and googled but haven’t come close to an answer. If anyone could please help that would be great, thank you in advance.
Connections at both ends of both big cables need to be secure and free of corrosion or debris. There could be corrosion inside the cables - the copper becomes green and crumbly. If cleaning and securing the ends doesn’t work and the cables themselves are in good shape, then the ignition switch and the starter motor - its solenoid, especially - become the most likely suspects. Good luck and please keep us informed.
Just because the battery reads 12.5 volts does not mean it’s good. Most parts stores will test properly for free.
The ‘disconnecting then reconnecting the battery’ relationship to the no-crank is a major clue. You could have a loose connection in those cables, possibly hidden by the insulation, and manipulating the cables is enough to get it connected again, temporarily. Next time it happens instead of disconnecting the battery, try manipulating the cables instead, twisting and pulling etc,. See if that works. This all presumes the battery posts and connectors are clean and properly tightened of course.
If not, your best bet is to measure the voltages at the starter motor during attempted cranking. Both terminals should measure at least 10.5 volts, terminal to case. If they do and it doesn’t crank, replace the starter motor. If one or both don’t measure that much, works towards the battery to find out why.