i have a 1990 2.9 ext cab 2wd. I have changed the alternator and the battery but my charge light stays on? Any suggestions on what is going on?

 

Welcome to the forum

You need a volt/ohm meter, under $20 and it will save you hundreds of dollars over its life.

Battery Light is the ON/OFF switch for the alternator

On the alternator there will be a 3 wire connector, this is plugged into the internal Voltage regulator.

White wire, it is a short jumper wire to Stator, it needs to be plugged into separate connection on alternator.
Yellow wire, this is monitor voltage, it tells voltage regulator if vehicle needs more or less amperage

Green wire, this is the ON/OFF wire, runs directly to Battery Light in the dash.
Battery Light bulb gets 12volts when key comes on
Green wire at the alternator is a GROUND when alternator is OFF
So Battery Light bulb comes on.

When you start the engine and alternator starts to "make voltage", the Green wire is no longer a GROUND, so Battery Light bulb goes off

So here is the way to test if alternator wiring is OK
Get a Volt Meter and set it to DC Volts, it will have a Black Probe and a Red Probe
Key OFF
Test Battery Voltage, should be 12.3v to 12.8volts(new battery 12.8+ volts)

On the back of the alternator is the B+ terminal, put Black Probe on alternator's Case(metal)
Put Red probe on B+ terminal, you should see Battery Voltage, exactly
If not then you have bad fuse or fusible link, 1990 fusible links, there may be two, they will be attached to Starter Relay's Battery Post
(starter relay is often referred to as starter solenoid)
Battery-----red cable-----starter relay post-----(fusible link, 2)--orange wire(2)------------B+(alternator)

Unplug the 3 wire connector
Test Yellow wire, Black Probe on case, Red Probe on Yellow wire's contact, you should see Battery Voltage
If not you have a blown fuse, it will be a fuse in engine fuse box, labelled ALT

Test Green wire, same as yellow wire, should be 0 volts
Turn key ON, engine off
Green wire should now have Battery Voltage, may be .1 or so less, thats OK
If not then wire is shorted to ground

If all wires test OK then alternator is bad, doesn't matter if it is new or not, system is not all that complicated, if you test the wires and they test OK then alternator, new or not is the problem.

 

thank you for the information. I'l try it all out in a couple days, and let you know of the findings.