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Intermittent alternator issues recently, had tested and the

regulator was failing. Replaced the...
Intermittent alternator issues recently, had tested and the regulator was failing. Replaced the Optima Yellow Top I've had up front for 7 years without problems with a new AGM battery, and also upgraded the Big 3 wires. Alternator is only putting out 11.5 - 12.3volts, and the battery light does not come on with ignition is switched on. Sounds like a wire connection issue, perhaps the pigtail from the fusebox to the alternator? I've tested the connections from the battery to the alternator, and with the main + wire from the alternator to the battery disconnected while the engine was running, it was only producing 12v when I tested via my multimeter
JA: Have you tested the battery? Have you tried testing the alternator?
Customer: yes
JA: What year is your Optima?
Customer: 8/2011, it tests fine
JA: Are you fixing your Optima yourself? What have you tried so far?
Customer: I'm not using the optima as my primary/starting battery anymore, replaced it
JA: Anything else you want the mechanic to know before I connect you?
Customer: No. The alternator was charging at 14.5 volts after replacing the optima and the cable from its + to the alternator terminal.
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Answered in 6 minutes by:
9/11/2017
Ted Ritter
Ted Ritter, Toyota Master Tech
Category: Toyota
Satisfied Customers: 4,469
Experience: Toyota Master Tech, ASE Certified
Verified

Thanks for posting

What is the year and model of this vehicle please?

With all wires connected you are measuring 11.5 to 12.3 volts at the battery, is this correct? Most Toyotas have a 7.5A alternator fuse, has it been checked?

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Customer reply replied 2 months ago
Mine is a 2004 Tacoma 3.4 TRD. The alternator was replaced last January after it failed (was replaced 6 years prior). The voltage it produces right now is when the motor is running; at idle and cruise. I was under the assumption it has a 120 amp alternator fuse; at least thats the one in the under hood fuse box. Can you explain what the wires to the alternator from the battery, the fuse box to the battery +, and the fuse box to the alternator terminal are for? I've read that the pig tail (3 wire round oval harness from the fuse box to the alternator) sends an initial "excite" charge when starting the vehicle, as well as sense the alternator connection to illuminate the dash light if necessary. Something is causing the alternator to not charge at 14.5v right now, as well as not light the battery indicator on the dash when the key is switched on. I am going to replace the alternator this week, but if I dont narrow down wiring issue also, I'm confident the problem will still be present after the swap
Customer reply replied 2 months ago
If its easier for you, I dont mind speaking by phone
Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
Satisfied Customers: 4,989
Experience: 30+ Yrs of auto experience, Award Winning Svc. Manager; Just Answer Customer's Choice Award Winner
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Hello. Different expert here. Perhaps I can assist you. Please advise if you still need help on this issue. Thanks

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Customer reply replied 2 months ago
still need assistance. I've done more reading today and am certain its a wiring problem between the fuse box and the alternator, or the fusebox and the battery. Can you tell me what the function of each wire here does, with the exception of the 3 wire harness that connects the fusebox to the alternator? I'm familiar with the excite function of that; if there is anything else about it, feel free to let me know. I'm pretty certain that the main lead from the battery + terminal to the alternator is the charging output back to the battery, correct? I tested it yesterday by briefly removing its connection to the battery's + terminal (leaving it connected to the alternator) and checked its voltage using my multimeter; it was 12.2 volts.
As of right now, when the ignition switch is on and the motor is off, the battery dash light is off and never does come on when the ignition is switched on so there doesnt appear to be any voltage running across that circuit.

Let's do this first: Remove the negative battery cable from the battery terminal post. Place the negative lead of your voltmeter on the disconnected negative battery cable. Touch the red lead of your voltmeter to the battery negative terminal post. Advise of the reading you get.

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Customer reply replied 2 months ago
This is for resistance, yeah? I'm headed home now, would it be simpler for me to have you call me?

No. We need to check voltage and amperage. Not resistance.

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I will set the phone call offer screen for you when you get home

Toyota Service
Toyota Service, Toyota Expert
Category: Toyota
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Customer reply replied 2 months ago
12.68 volts with the motor off, tested as you specified. It's been on a trickle charger all day too
Customer reply replied 2 months ago
I entered my phone number and clicked continue but nothing happened
Phone call session started
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