2003 mazda protege

With key on engine off (KOEO) if I load the power window circuit, my voltage goes from 12.6 volts to 10 volts. This only occurs if I continue holding the window switch down after the window hits the bottom of its travel. When actually rolling down voltage only drops to 12.4v which is normal.

With key on engine running (KOER) if I turn on my headlights there is a noticeable rpm drop although it is slight. If I conduct the same window switch test with the headlights and engine on the headlights dim out and the alternator doesn’t seem to “pick up” lost voltage. Even accelerating from a stop the headlights will dim out and then brighten back up. All grounds are functioning properly with no resistance. Primary power cable is working properly with no resistance faults.

the only thing I can think of would be that the alternator had a large amount of water splashed on it and the main fuse (100A) blew. I replaced the failed alternator and the main fuse. Not sure if the fuse block was damaged or if any wiring was harmed although no other fuses were burnt.

battery tested fine when I conducted an internal resistance and load test with my professional testers.

 

Your battery needs to be load test. Again ! Then go from there


That much a drop in voltage in your first line points to the power supply , Battery.

Dont assume your tester is not problematic until you test another known good and bad battery . The real company you choose for a user name run same test different diagnostics equipment.
Or go have it tested at a parts store that offered free battery testing.

 

Ya I understand that but I have tested other batteries with this tester. I think the battery is indeed fine but I will run the test on a different shop tester just to be sure. Testing voltage at the switch and at the battery both have the same voltage drop so maybe it is the battery. I will test and report back.

 

You seem to know a little what your are doing. So look at your load tables for a 12 volt battery . You should not be drop in the 10's starting or if the engine is normal just running with no accessories or light on. So you either have a continuity problem that must be found or you have a failing battery. Just because you tester shows fine on other batteries tested this is where you need to confirm your tester is still accurate.
The prime suspects with your issue:
If your battery is in GOOD condition and you confirm that the terminal connection are clean with good contact and the ground at he frame or engine is making good contact and the starter cable from the battery to the terminal on the starter is clean and good contact then you have a alternator issues (not totally uncommon with rebuilds) or a bad voltage regulator of a mystery load that you need to track down using a digital volt ohm gauge and a scanner connected to your OBDII connector to check for any DTC or anomalies.?

 

here’s the thing: if my engine is not running but ignition is on so the electrical systems are operational, and I perform the test it will still drop voltage. So it’s not related to the vehicles charging system

 

Never rule out anything without testing first!
But...

I need numbers?? Stabilized voltage of battery no load. Battery voltage ONLY turning on ACC position of ignition?

 

battery idle with no load on it is 12.65v
with ignition switch set to acc it is 12.6v
with ignition switch set to on but engine off voltage is 12.45v

rolling down window voltage is 12.30
once window hits the stop and stalls like they all do voltage drops to 10v flat

 

Guessing! This may be a power wire that is not circuit protected exposed? Either from wear damage from rubbing caused by engine and transmission movement (broken or word mounts0or a rodent issue chewed into your harness.
I would also pull the door panel and feel/touch the window motor or use a Mini Temp like Reytech to measure the temperature of the motor and surrounding wire and harness. Also check the relay for the window motor.

At this point I am reaching and guessing which I do not like to do so aside from everything we talked about there comes a point on a forum and trying to solve some issues must be done in the real world!

 

I rechecked my numbers. The voltage drop at the actual battery terminals is only 0.2 volts… at the window switch if I test voltage for the power and ground wires going into the switch it drops from 12.6v to 10v… if I use the nearest multipoint chassis ground instead of the ground going into the window switch voltage only drops to 11.1v

i think this may be a ground fault. Sorry for the misleading info I was very tired this morning and not thinking clearly lol