I just bought a 1977 f150 with a 351w I'll post more info on it later. I went to start it yesterday morning to see how it did in the cold. It started right up and warmed up in a few minutes. I killed it walked a way and 2 hours later I went to drive it a little and all I heard was a click. I tested the battery and it only had 12.8 volts. I jumped it and nothing. Just a clicking noise. I tested the cable going from the solenoid to the starter and it had continuity. I replaced the solenoid an hour ago and still the same thing. I tried jumping it again and still the same thing. I then used a jumper pack that was fully charged and still the same thing. I cleaned the battery terminals and connectors. When I go to turn it over the lights go dim and once I release the key the brighten up. What is weir is sometimes the cab light will stay dim and same with the dash lights but when I turn the ignition off and back on it goes back to normal. When I turn the key off the voltage regulator makes a click as well. I'm not a master when it comes with older engines but I now my stuff and honestly, I haven't got the smallest idea on what could be wrong. I'm thinking the battery, starter, or ignition. I need help!!!!

 

12.8 volts is a healthy voltage, but it can be misleading. If the battery is dying, it can dump when you pull current. If the battery is dead enough, it can prevent the vehicle from being jump started. Measure the battery voltage while the key is held in START.

 

It was reading 12.2 I turned the key and it jumped around to 12.1 and 12.0

 

I don't have anything to measure amps, so I can't test the starter. I did try to bypass the solenoid with a piece of wire. The voltage regulator clicked and that's it.

 

It is either a dead battery or you didn't clean the terminals well enough. My truck did the exact same thing

 

Just checked all the connections and tried a different battery that came out of my other truck and still nothing.

 

try crossing the posts on the solenoid, I've had cheapie solenoids not work right out of the box

 

Never do either of these things. Something is not adding up. If you're only dropping a couple hundred millivolts with the key held in START, then it doesn't make sense why your headlights dim. It's one or the other. Something is not being communicated clearly.

 

OK, if your getting a real good click and the headlights are dimming the starter is more than likely shorted or the cable between the solinoid and the starter is shorted to ground, if the cable is clear, swap out the starter.

 

I managed to fix it. I replaced the battery terminal clamps and the wire from the battery to the solenoid.

 

Glad to hear you got it worked out.