Hi I have a 2003 mondeo and when you try to build up speed in 3rd or 4th the coil light comes on and losses power but if you turn the car off and back on all find any ideas please 

Hi Tony - Welcome to the Ford Owners Club.

What do you mean by the "Coil Light" ? Is your car petrol or diesel?

Sorry coil light it’s diesel 

Do you mean the Glow Plug warning light. It's normally an orange light looks like a spring lying on its side ?

Yes that is the one lol

In that case I would guess that you have a fault with the Glow Plugs. What mileage has the car done?

It has done 209.000

Holy S*** I didn't know that the dashboard could count that high 🤣

You possible have one or more of the glow plugs failing. I don't know how much of a mechanic you are but if you're up to it, take them out and inspect them. you can test them with a multi-meter for resistance but I wonder if one or more is mechanically damaged.

Coil light means the ecu has detected a fault and logged it in memory.  On a mk3 Pre-facelift and early facelift models, they're NOT OBD2 compliant, so to reliably read the codes you need a code reader from Tunnrat electronics (around £20) or a Fordiag from Czech Republic (around 90 Euros) both run on Windows (you'll need a laptop with USB port) , but Tunnelrat they also do  an Android one.  On a mk3, the glowplugs won't throw up an error code if any of them are faulty. At that mileage, it could be fuel pressure related... re-reading the original post, that losing power is known as  limp mode.  Is the fuel filter overdue for changing? I had a faulty/worn accelerator pedal that was bringing on the light, and it also caused limp mode, but without reading the error code I wouldn't have had a clue what the problem was. (mine's an 02 mk3)