Bought and replaced battery and connectors just yesterday in my '98 F-150. It turned on fine the first three times I started it up, but now I’m just getting the click and dashboard lighting up. I dont think it would be the alternator since I replaced that about a year ago as well. Thoughts?
The problem might be with the starter relay.
Get a voltmeter and measure the battery voltage. Less than 12 volts? Jump start the truck, measure the voltage again, less than 13.3 volts or so, likely your alternator IS bad. Test, don’t guess.
The basic battery/alternator test is to measure the battery voltage before first start of the day. Should be around 12.6 volts. Now start the engine. Should measure between 13.5 - 15.5 volts. If that’s ok, and if all the good ideas above fail, look under the truck. There’s probably two wires that connect to the starter motor. A thick one, and a thin one. Measure the voltage on both when the key is in “start”. Measure between the terminal and the starter case. Both should measure at least 10.5 volts. If they both do, and it doesn’t crank, then the problem is most likely a faulty starter motor. If one or both measure less than 10.5 volts, work backwards from the starter toward the battery to find out why. Starter relay, clutch/tranny safety switch common causes. Good idea on a 98 to first double check you have a good solid ground between the engine and the chassis, and between the chassis and battery post negative.