Battery draining while driving. New alt and battery stays charged in other vehicle

Since the alternator and the battery are both new, there should be no reason the battery is not charging while the vehicle is running. Check the B+ or Output of the alternator. You might offend your mechanic by suggesting this, but it is your vehicle, and electrical things usually equal expensive diagnosis. You can kinda see and feel this area from above, but you really need to be underneath. This is the bolt looking thing on the end opposite to the pulley. This bolt is longer than the area the nut sits AND the nut might be a touch loose. The wires that go on that should have an eye-like end that slides over that bolt and will seat on that location. If this connection was not tightened correctly the alternator can not charge the battery. Make sure there is a flat locking washer and a nut on the end of that bolt. Tighten the nut, but don't go crazy. Firm. Then snap on the insulator cap that is attached to that wiring. Push it until both sides snap. If the insulator is not on correctly, it will come loose. The B+ is a pretty warm place and without that insulator it can melt nearby wiring. Makes a bigger mess if it is overlooked.

Seen this "mystery drain" many times. Check spark at the battery to see how big the drain is. For this simple test, blow away any (explosive) battery charging fumes. Leave one terminal on and gently touch the other to its post in fairly dark surroundings. Then try it again with the wires taken off the alternator. Your spark is now probably much less. Usually bad diodes leaking electricity backwards through the alternator cause this drain. Replace the alternator or the diode pack inside it. Some mechanics recommend actually measuring the drain.... hahaha. OK whatever.

The alternator may charge fine but could drain the battery through a bad diode,have you checked the alt for a bad diode?Disconnect the battery positive cable.Put a regular 12v test light between the battery positive post and the positive battery cable.If the test light is bright you do have a drain,if dim it is OK.A dim light may mean the drain is internal in the battery.If you do have a bright light remove a fuse ,one at a time from the fuse box until the light goes dim.Once dim you have identified the bad circuit.If removing all fuses do not dim the light,disconnect the alt charging wire at the alt,if that dims the light,then you do have a bad diode.DO NOT create a drain(bright light) when checking for the drain by turning on the key or opening a door/trunk etc.
Also,do an overnight battery check by disconnecting the battery overnight,if things are fine the next morning after the battery was disconnected then it is a drain in the vehicle,if the battery is dead even after being disconnected overnight,,then the battery is bad.

Check the battery voltage when the vehicle running on idle, it must between 13-15 volt.
Check the battery voltage on full electricity load (turn on headlight, A/C, radio, wiper), it must between 12,6-13,8 V, If the voltage under 12V, check the radiator fan and radio/power amplier

its the alternator problem

Check the drive belt tension and wiring connection at the alternator and at the battery. Check for a blown fuse in the fuse block . -hope this helps

As the car re-started, the battery is not flat.
The voltages measured indicate a problem with either the power or ground connection in the circuit between the alternator and the battery.

You likely have a intermittent / poor ground connection somewhere in the power system.
Check battery terminals are clean and firmly attached.
Check battery cable and alternator ground connections are intact and in good order.

Sounds like you regulator points are staying closed, thus causing the no-charge condition as well as the severe drain on your battery. Check the fusable links, the ES1 and ES2 motors were famous for this in 82-85, but if they are fine, replace your alternator.

Kevin

Generator with Integral Rear Mount Voltage Regulator, Internal Fan Type With the key in the RUN position, voltage is applied through the charge indicator lamp I circuit to the voltage regulator. This turns the voltage regulator on, allowing current to flow from the battery sense A circuit to the generator field coil. When the engine (6007) is started, the generator (GEN) (10346) begins to generate alternating (AC) current which is converted to direct (DC) current by the rectifier internal to the generator. This current is then supplied to the vehicle's electrical system through the battery positive voltage (B+) terminal located on the rear of the generator. Once the generator begins generating current, a voltage signal is taken from the stator and fed back to the voltage regulator S circuit, turning off the charge indicator/lamp. With the system functioning normally, the generator output current is determined by the voltage at the A circuit. This voltage is compared to a set voltage internal to the voltage regulator, and the voltage regulator controls the generator field current to maintain proper generator output. The set voltage will vary with temperature and is typically higher in the winter than in the summer, allowing for better battery recharge. With the system functioning normally, the generator output current is determined by the voltage of the A circuit (battery sense voltage). The A circuit voltage is compared to a set voltage internal to the voltage regulator, which controls the generator field current to maintain proper output. The set voltage will vary with temperature and is typically higher in the winter than in the summer, allowing for better battery recharge in the winter and reducing the chance of overcharging the battery in the summer. A fuse link is included in the charging system wiring on all vehicles. The fuse link is used to prevent damage to the wiring harness and generator if the wiring harness should become grounded, or if a booster battery with the wrong polarity is connected to the charging system. Mitsubishi 215-Ampere Generator
The Mitsubishi 215-ampere generator is an internally regulated, brushless unit that is self-current limiting and temperature compensating. The regulator is integral with the generator and the fan is external.

VISUAL INSPECTION CHART Mechanical Electrical

• Before attempting to test a battery, it is important to give it a thorough examination to determine if it has been damaged.

• Batteries are tested to determine the state of charge and ability to crank an engine. The result of these tests is to show that the battery is either good, needs recharging, or must be replaced.

• Preliminary checks to the charging system should be made regardless of the fault condition. These checks include:
  • Check the fuses/fuse links to the generator to ensure that they are not burned or damaged. This condition, resulting in an open circuit or high resistance, can cause erratic or intermittent charging system concerns.
  • Check battery posts and cable terminals for clean and tight connections. Clean the posts and the cables to ensure good electrical contact.
  • Check for secure connections at the generator output, voltage regulator and engine ground. Also check the connection at the power distribution point.
  • Check the generator drive belt to ensure proper tension and no slip between the generator pulley and the drive belt. Refer to Section 03-05 in the Powertrain, Drivetrain Manual.
  • Check battery for full charge.

• Before performing charging system tests on the vehicle, note conditions such as: slow cranking, discharged battery, charge indicator lamp stays on with engine running, charge indicator lamp does not illuminate with ignition switch in RUN and engine not running, etc. This information will aid in isolating the part of the system causing the symptom.
• When a relatively new battery is discharged, test for current drain. The following are some of the most common current drain concerns:
  • Glove compartment lamp stays on with the door closed.
  • Engine compartment lamp stays on constantly.
  • License plate lamp or interior lamp stays on constantly.
  • Other electronic component concerns.

hedlight switch bad......