Car wont hold charge

You'll need an inexpensive digital voltmeter to test the system. Start by charging the battery for a half hour or longer on slow charge. Measure the voltage after removing the charger. If it reads near 12.6 volts, the engine should start and stay running. If it doesn't, suspect dirty / corroded battery cables. A common problem on Fords is a corroded cable under the insulation of the cable that attaches to the starter.

If the engine keeps running with the charged battery, measure again while it's running. It must be between 13.75 and 14.75 volts. If it's low, we need to test the voltage on the yellow and green / red wires on the back of the generator. The yellow one must have 12 volts all the time. If not, check for a blown blue 15 amp fuse.

Caradiodoc

If you recharge your battery, will it start and maintain the engine?

You gotta charge the battery without the engine running. Give it a good half hour at the very least. If the engine runs with a charger or another car connected, you know it will run with a charged battery. It doesn't matter where the current is coming from. When it dies when the charger or booster car are disconnected, that means the battery didn't recharge while those things where connected. What you should also find then is the head lights, dome lights, and radio, etc. Don't work either. Measure the battery voltage to double-check. If you find around 12.0 volts, the battery is good but discharged. If it is closer to 11 volts, there is a shorted cell and it must be replaced. From your description, it suggests dirty or corroded battery cables AND a problem with the generator or its wiring.

Caradiodoc

Yup, that's a possibility. That's what the yellow and green / red wires plug into. Once the engine is running without a charger, there are tests to determine if the regulator is the problem, but first check for 12 volts on that yellow wire. If the battery light on the dash is on when the engine is running, that green / red wire is ok.

Caradiodoc

To add to this thought. An alternator will not recharge a battery if it is too dead.

Let me know what you find.