got battery trouble

[mean machine]

hey guys and gals i have a 89 ranger with the 2.9 and 5 speed the problem i noticed today is that the battery idiot light was lit up but the volt gauge showed normal charge ever with all the lights and stuff on but if i wiggle the key it goes out what is it cant figure it out checked batt termanals and ground connections and all of the connectors on the alt it doesnt allways do it just once in awhile please help jason

 

[RonD]

Check the wires on the back of the alternator, look for frayed or loose connection.

If it all looks OK you will need to check the key switch.

I would first get a Volt meter, and check the battery voltage when light is on, that light also comes on if too much voltage is being sent to battery.
Engine at idle should show 13.6 volts, approx.

Voltage should never be above 15 volts or below 13.4 volts with engine running.

 

[mean machine]

well i didnt actually check the battery voltage when light is on but the volt meter on dash didnt move from where it usually is at which is about 1/2 the way up the light comes on and goes off at random but the gauge never moves

 

[Andy D]

Get yourself a volt/ohmmeter and read the instructions. This goes for everybody.

 

[hondaxr650]

Wiggling the key making the light go out makes me lean towards a bad ignition switch. Replaced a lot of switches under a recall back in the 90's.

 

[naford]

+1

 

[mean machine]

ok guys i think i figured it out i noticed it only does it with heater on high or the ac max on if its off the light is off i noticed it today going to work but the volt meter on dash stays in the safe rang yes it moves down a little when heater is on high but it does come back up ?? all other positions its ok low and med its fine im thinking heater switch or resistor?

 

[RonD]

Dash volt meter going down when heater fan is switched to high is correct and then back up just after is also correct, that means voltage regulator is working.

Voltage regulators job is to keep alternator from burning up the battery, i.e. sending it 15volts all the time.

Voltage regulator is set to send battery 1 volt above it's at rest voltage.
If battery's voltage is 12.6 volts with engine off, then with engine running it should be 13.6 volts
When you turn something electrical on, voltage drops below 13.6 volts so voltage regulator increase the voltage in the rotor(alternator) and increases the alternators output to get voltage back up to 13.6 volts.

Just as an FYI.
Inside all alternators are 3 fields, these are what generate the power going to the battery.
These are separate circuits and one or two can fail over the life of an alternator.
Headlights dimming slightly at idle usually means 1 field has failed.

This means the voltage regulator has sent all the voltage it can to the rotor and can't keep the voltage at 13.6 volts, so it drops to 13.1 volts and you notice this as lights dimming