ScottsGT

I need a little assistance from someone that has an ES without the dreaded alternator killing symptoms. There is no way I have killed 4 alternators in the past month without there being a problem. FYI: 1999 ES300

What I'm needing is the voltage read off of one of the 3 wires that plug into the alternators voltage regulator.
Key off reading.
it's the yellow wire I'm needing the voltage reading off of. Just unplug the connector from the alternator and take the reading inside the plug.
Center should be 0V
White (looks tan due to age) should be 12V

Hopefully this will diagnose my issue that I have either pinpointed back to the ignition switch or the Integration Relay. I just needing a good, known voltage reading to verify my suspensions.

ES300NZ

There are three wires to a toyota alternator.
- Switched Power, IG terminal - Ignition switch that turns the voltage regulator on (only live when IGNITION IS set on/run
- Constant Power, S terminal - Senses battery voltage
- Earth connection for alternator light. L terminal - Closes the circuit to the warning lamp

Find the wire that has an earth connection which turns off when the car is running (if you want to check for that)
Test the other two wires. Are they both 12v+ when the car is just sitting there ?
Something is wrong with the car, it has decided to send power down the IG wire and that it's baking out your alternator.

(possible high resistance) - If not, check all earth connections on the engine, are they good wires ? heat soaked ? if bad replace.
(possible high resistance) - Then check the condition of the wire which is called B, the output wire. Does that have high resistance, or looks damaged / heat soaked (if so replace).
(Part Failure) is there a failed part in the system, test each part linked to the alternator one by one.

How are the alternators dying ? are you over tightening the belts and killing the bearings ?
Do they stop charging ?
Do they short out ?
are you draining battery's ?

The voltage down a wire doesn't tell you much unless you understand the operation of the system. The attached document covers the charing system in your car nicely. It says 1994, but the 1999 has the same system.

pauloil

you most likely have bad wires as stated. the positive cable can be checked with a voltage drop test: google this and read how to check your wires under load. on this site there are posts how to do the voltage drop testing. look for these, and good luck