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I think I would attack the drain problem first. Something has to be draining the battery, it does not have to be a steady drain. It could be something serious for 30 min in the middle of the night. You may need to pull fuses one at a time to try to narrow down the circuit. it could even be a weak component in the alternator or computer. I know you said you replaced the alternator. If it goes down overnight, it should also go down during the day. Can you leave the meter connected and check it every hour or so ? ? Another component that could be suspect is the key switch. I know you said you checked it, but it could be a part-time problem. When the starter or relay clicks, I would want to know how much voltage I have at the starter post, and coming out of the key switch. Then how much at each point in between. You also have a neutral safety switch in that circuit.
Its not the starter. Could be a long list of things - a mechanic would check for drain by disconnecting the battery and using a test light or VOM to check each circuit. Common items are small lights and stuck relays.
Have you confirmed by going out to the car at night that none of the interior lights or lighted visor lights truck or hood lights are staying on? That is by far the most common cause of a battery drain. Other less common cause is a defective alternator rectifier diode Disconnect the battery overnight as well to confirm you don't have a shorted battery cell, that to will run the battery down, it is called an internal drain. Also make sure the top of the battery is clean of any acid.
leaving the radio on all night would not cause the battery to drain away like this providing its a good one .try disconnecting the battery overnight and see if it still drains as sometimes a battery can drain flat on its own which is caused by sulphation across the internal plates in the cells ,then if if it starts the next moring the battery is ok ,so next is to discoinnect the alternator large terminal off the alternator and try that and if it starts the following day renew the alternator as a rectifying diode is down running battery flat ,if still a proble then out comes the tester to look for a relay that has the contacts stuck together or the favourite boot light but this is a pick up truck so i would suspect the alternator
Pull interior light fuse and the clock fuse, then disconnect the NEGATIVE battery terminal, and place a volt meter in between the terminal and the cable... There should be very little current. You can also wire a light in between the batt and cable, if no voltmeter is available.
Most common issue is diodes in the alternator. Alt can test okay on some tests, and still have an issue. Failed diodes leak power to ground.
So, keep disconnecting stuff until you get no voltage at the meter or light in series with the battery and cable...
With this method, you should be able to find the culprit.
BATTERY VOLTAGE CAN DRAIN THROUGH STARTER RELAY OR BAD DIODE IN THE ALTERNATOR.I WOULD REPLACE THE STARTER RELAY.I AM LOOKING AT A ELECTRICAL DIAGRAM.YOU HAVE A 40 AMP IGNITION FUSE THAT FEED THE STARTER RELAY.IF STARTER RELAY HAS A SHORT IN IT.IT COULD DRAIN THE BATTERY.
If you are jumpering the starter, then the battery is not being drained, the starter may have a bad solenoid.
If the problem still is a dead short, a painstaking troubleshooting is required.
Remove one fuse at a time, check for voltage drop, and see which one is the culprit. Then you woud have to locate each item on that circuit and trace the wires for one that is broken, or pinched & contacting ground.
Also, check at night or in a dark garage, as trunk, door, or hood pin switches may be stuck in the open position - and will keep the lights on.
Interesting note - your having to jumper the solenoid on the starter indicates a possible worn/damaged ignition tumbler. If your tumbler is not seating on the OFF detent, your ACC may still be left on even with the key out of the ignition.
Try disconnecting your alternator temporarily. It may have a shorted diode but that would also normally drain the battery too unless it charges over a relay.
The starter relay can't cause this alone and the currents through the ignition switch mostly control relays.
If removing the alternator cable didn't work, I would remove the starter (only a few bolts) after disconnecting the ground cable from your battery and try turning it by hand.
It should be stiff but not impossible and if it refuses to turn, it may have a short from the field to the case.
It isn't really possible to use a multimeter to check the starter's windings because they are very low resistance when normal (the beast draws 120-200 amps to start) and would look like shorts on a standard meter anyhow.