Well, let me start off by saying I am new here and not a big car person! Although, i am trying my best to really get into the whole concept. I can only do the small basics on vehicles, but always learning new stuff. So, now what brings me here. My brother has a 1988 F250 4.9L Fuel Injected Straight 6...it has sat for about 3 years but ran STRONG before she sat. I am looking to buy it off him now and get her all pretty, but looking to get her running first. When i turn the key, nothing happens at all, as if the battery was completly drained. From there i tested the battery which was good. Then i took the starter off and got that tested at Autozone which was also good. Then i had a friend who knew a little bit about trucks come look at it, and i believe what is called the relay? right above the battery, he tried to jump that and when we did it would make loud clicking noises which he said was good. So, i am out of ideas on what to do and need your help! Oh, also i tried to give it some extra juice before all this by jump starting it and when that was hooked up i had a little power to the lights, but when i attempted to turn it over it would make one short click then nothing. Any advice would be appreciatted! SORRY for making this so long haha. Thank you!!!

 

You stated the battery tested good, but you didn't mention if you charged the battery fully. Even if it was charged and tested good, it might need to be replaced after a long period of sitting without use. The plates inside the battery can become sulfated and the battery will not work.

To rule this possibility out, replace the battery with a known good one. Maybe see if you can borrow your friend's battery. The jump starting idea was good, but if the truck's battery was not really discharged, it would be hard for it to jump without letting it first absorb some charge by letting the running vehicle run for awhile at about 1500 rpm to give the truck battery some juice. The fact that the lights were only dimly working means that you did not have full voltage, we need to get full voltage from the battery before ruling it out.

The clicking from the starting solenoid relay is a good sign, it should make one solid click and the engine should begin rotating. If it clicks with no engine rotation, it is usually a sign of a weak battery.

The battery in my truck recently died, and I tried to jump it using a spare battery. It wouldn't work, it acted weak. So I installed the spare battery and it started fine. The jumper cables result in a lot of lost voltage and the already weak battery in the truck may be lowering the voltage further when you try to jump it. So that is why I suggest installing a known good battery.

If the known good battery doesn't make the engine rotate strongly, let us know your progress.

 

I did forget to mention, that my friend did bring a strong battery that was fully charged and it did the same thing as the battery that was in it. Well, I should also say that the battery that is in it, is fresh from a van. So both batteries were good. Im no car major so all i can think of is some cables running to the relay or starter is what may be causing the problem? Maybe because its still getting power to lights and such, the cables may be corroded inside the insulation? What do you guys think?

 

If the battery is good, and starter is good, then it is either the cables or the solenoid relay is bad. Usually, if the solenoid clicks it is working, but it can fail. You can bypass the solenoid relay by connecting the two large terminals together with jumper cable, which will cause the starter to engage, and the engine to rotate if the battery cables and starter are all good. There will be sparks created if you bypass the relay as described. Be careful. If you get good cranking speed with the relay bypassed, the solenoid relay is probably bad.

There is a small wire to the solenoid relay that is powered when the key is turned to START position. You can use a test light to see if the small wire gets powered when the key is in START.

You can also try jumping power from the positive battery cable to the small stud ("S" terminal) on the starter solenoid relay where the small wire connects. This should cause a strong click and engine rotation. If you turn the key to RUN position, then jump power to the small stud, the engine should rotate and start.

There are some good tips for testing the solenoid in the video below:
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You can find more videos by searching "Ford solenoid" and similar terms on youtube.

You did not mention if the engine rotated when the solenoid clicked. Is it rotating at a proper starting speed? Rotating at all?

If you see a lot of corrosion in the cables, go ahead and replace them all. I replaced the ones on my 88 because the insulation on the cables was cracking apart badly, and the positive cable could have touched the fender and grounded out, causing a serious meltdown/fire. I did not find a lot of corrosion, but yours could be a different story, it depends on how much salt and moisture the truck sees.