I'm a new guy here . I need to pick someones brain, in regards to a simple test that will let me know if my alternator on my 2003 E-450 Super Duty, with a V-10 is the problem. I recently put a new battery and a new starter in , because of start problems. Within the last few [2] weeks it has not wanted to start, Wouldn't start with a jump so I used my hot box.The other night It died, and It cost me 200.00 for a tow. Also just to let everyone know I had battery and starter tested at the auto parts store, also checked all grounds, fuses, cables . Any body got any Idea's ? Thanks Angelo

 

It's very easy to test your alternator.

Using a voltmeter or multimeter set to it's voltmeter function,
set the meter to an appropriate measurement range (you'll be expecting on the order of 10-15v DC) hold the red (positive) lead from the voltmeter to the positive (red) terminal on the battery and the black (negative) lead from the voltmeter to the negative (black) terminal on the battery.

Do this while the engine is not running.
If you're seeing 12.6-12.8V, then the battery is fully charged and is not your problem.

Now try taking the measurement again with the engine running. If your alternator is operating correctly, you will see a higher voltage this time-- in the range of 13.6-14.2 or thereabouts.

You would be wise to double check those connections if they were first checked by the guy at the auto parts store LOL........ Especially check the two big connections on each of the starter relay and the starter itself.

A non-operational alternator will not cause your vehicle to not start, as long as the battery is charged, or another source of power such as your "hot box" is present. The alternator will simply cause the battery to discharge as the engine runs and fail to run/start later.

You may also have a short which is straining the alternator or draining the battery...... Use an ammeter, disconnect one of the battery cables (with the vehicle not running and all electronics turned off... such as radio, lights, etc)
and connect the ammeter in between the battery terminal and the end of the cable which you disconnected.
Any substantial amount of current flowing means that something is drawing power that shouldn't be. Don't worry about milliamps, only a more substantial amount of current. Tiny amounts of power are of course used at all times by the computer and clock etc in the vehicle, whether it's running or not.

Good luck,
And while I'm certainly not trying to bash you by saying this... just trying to be helpful--- Please try a quick google search before asking a question as elementary as this.... There are a thousand youtube videos out there which will quickly demonstrate this procedure for you.
If you can't quickly and easily find the answers you're looking for, THEN come ask here.

Take care!

 

Oh yeah... and just to reiterate: If I were you the first thing that I would check after testing the battery voltage(if the battery is charged, then your no-start problem is not a battery or alternator issue) would be the connections at the starter solenoid and the starter.

I've experienced an intermittent no-start or very hard start condition due to corrosion at the starter solenoid connections before on my 1988 E-250.
A quick touch up with very fine sandpaper to bring the metal back to a nice shine on the terminal and connector corrected the problem immediately.