I have converted my l67 swapped 86 gt in the signature to OBDII from OBD1 using a harness from fieroflyer. After the swap I was driving the car and notice that my battery gauge was low and the car began to run like the battery was low. I got the car home where it died.

I tried to charge the battery and it would not charge overnight so I swapped it out with brand new one under warranty.

I noticed as soon as i connected the new battery that the alternator was humming faintly key on or key off it did not matter it made a humming sound putting a draw on the battery.

I started the car the gauge read 11v after a few minutes of it idling the voltage began to drop. So i pulled the alternator and had it bench tested which it failed (low dc volts and low stator volts) Replaced alternator with a cheap advanced auto parts reman unit no humming anymore!

Car ran fine at a solid 14 volts no issues for about 10 minutes. Shut car off thinking job well done.

Next day car started up just fine drove it a few miles to the gas station on the way I noticed the volt gauge was low again around 11-12 volts and dropping quickly.

parked the car shut it off and now the alternator is humming with the key off again drawing voltage again!!!

Took the new alternator off and had it bench tested and they are saying its fine.

I included a picture of my connector. Red wire is switched 12v, green does nothing, and orange wire is constant 12v. Is this correct?

By the way I spliced the red wire into switched 12v as it wasn't getting power at all before

Thanks in advance!



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Black 1986 Fiero GT, L67, 5 Speed, Firebird dash and door panels.
2006 GMC Sierra 2500HD LBZ Duramax
2006 Infinity G35 4 door (Wife's car)

[This message has been edited by CoFieroGt (edited 11-02-2014).]

I forgot to add that i have all brand new battery terminals and wires, and now brand new alternator and battery. System worked before the swap to OBDII so I am guessing that the problem lies somewhere in the wiring?

Wired wrong... And get a new connector.

Basic plan...
See my Cave, CS Alternator
and Alternator Sense show why S wire go to alt output.

If PCM controls the Alt then would need more data.

Battery must be charged full or CS alt won't turn on.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

[This message has been edited by theogre (edited 11-03-2014).]

Yes follow Ogre's advice. The L should not go straight to switched 12V, there should be a 30-500 Ohm load in between (usually provided through the lamp circuit on your dash).

The humming may be from a leaky/bad diode, shorted regulator. I don't know how the parts store tested your alternator, but it may be failing.

[This message has been edited by cyrus88 (edited 11-03-2014).]

Thanks Ogre so your saying run the sense wire to the post on the alternator?

Yes, 194 bulb is = ~52Ω resistor.
Is why LED here can cause problems. Many LED inline resistor are too much/little Ω.

Got it hooked up and working, I took the L terminal to the brake lamp output (switched 12v with the light for resitance) as my firebird dash does not have a battery light. And I ran the S terminal straight to 12v constant. Also that new alternator was fried probably from not having any resistance in the L circuit. Got it swapped and good to go! Thanks guys!