When you turn the key, there is a slight click but the starter does not engage, and then it’s just like the battery is disconnected – the lights won’t work, the dome light does not come on, etc. If I disconnect the battery completely and then reconnect it, the dome light and headlights work, but turning the switch produces the same result. I’ve tested the battery (it checks good) and I replaced the starter solenoid with one I had from a previous electrical problem, but no change.
First clean all the battery connections.
Just because the lights work doesn’t mean the battery is still good. Starting a car requires several magnitudes more amps then the lights. It may have enough power for the lights, but not the starter.
As Rod_Knox said…first clean the battery connections. If that doesn’t work…either jump the car battery or put on a battery charger to charge it. Once started, then drive someplace to get the battery and alternator tested .
If it still won’t start after battery is charged, then could be the starter. More and likely it’s a battery issue.
do you have over 12 volts on both sides of the starter solonoid when turning the key to start? the 1985 F-150 should have the firewall or fender mounted starter solonoid, so this should be very easy to check. This is also very easy to short across and see if the engine will try to kick over.
but, from what you are telling us- this sounds like a weak battery or loose/dirty cables or connections. Verify those are all good.
How did you test the battery to say that it is good?