I have a 97 f150, I have replaced the starter, battery and relays but when I turn the key the truck go's dead I have to keep boosting it and I'm at the end of my rope here what am I missing.

 

Need a bit of clarification

When you turn the key from off to start, the battery goes dead, as in < 12 V DC ?

Have you tested the battery ? Don't know if you replaced it with another or a new battery, could be a DOA battery if it will not hold a charge.

Disconnect the battery and charge it on a low setting until fully charged ( this would be a 2A setting, and take a few hours depending on how dead the battery is ).

Once the battery is charged, verify with a meter, is should show 13 + VDC ( usually in the 13.4 range ). Let sit ( still disconnected from the truck ) for 2 hours, and check again. The meter should show the same value +/- 0.2 VDC.

Let sit overnight, and check again, should be within =/- 0.2 VDC of the last reading ( or a max of 0.4 VDC from the complete charge reading post charge ). If the battery is in the 12.6 range it is questionable, but still considered OK by most. If the battery has dropped below 12.6 VDC overnight it is no good, and needs to be replaced.

Once you confirm the state of the battery as good ( will hold a charge on its own ) installed in the truck, when you turn the key from off to run ( do not start ) does the truck power up correctly ?

When you turn the key from run to start, what happens ?

 

Scully, I have to disagree with one statement, from my own personal experience. The Motorcraft batteries, when they were made by GNB (Gould National Battery) were some of the best I've ever seen as new car equipment. They routinely tested at least 12.8 when fully charged and load tested. Since about 2003, when GNB sold to Exide and Ford went to JC, they went to H*#l in a hand basket. Since JC controls about 80-85% of the battery sales in the U.S. now, they are all pretty mediocre to junk. I use JC because it's hard to buy anything that isn't made by them. MOST of those start out, if you're lucky, reading 12.6V when fully charged and load tested. It isn't very long for a good deal of them to start dropping to 12.5-12.4-12.3-12.2. They still seem to work OK but they DO NOT retain the 12.6V that they should (typically 2.1V per cell) (I know 2.17V is the technical # but it will not hold that on a STARTING battery) The '11 Camry at 13 mo. is the only one that I've had that actually would hold 12.6V at that age. (made by JC for Toyota) Even the 875 CCA Costco (JC) that I put in the truck less than a year ago will not now HOLD 12.6V. Even when I use the smart charger it will charge it to 13. or just over, but within a day or so it is already under the 12.6V. JC builds some of the best junk out there and they pretty close to have the market sewed up.