Hi Guys,

I've got an '85 Firebird that has been having charging issues for ages.

Originally I thought the issue was from shorts in the wiring from some very dodgy wiring, not sure if it was from the RHD conversion or from people playing with wires, but to give you an idea of the damage, the fuse panel rails were jumped with speaker wire.

I got sick of windows winding when they felt like it so I cut the whole fuse panel off and rewired everything to a 2003 Holden Commodore fuse panel to remove all the corroded and shitty wiring.

It took me about a week to figure out all the wires and get everything wired up properly and then had to buy a new battery because it was old and I think I killed it trying to kick over the car without power going to the fuel pump.

Replaced that and drove the car but wasn't charging, revved the crap out of it and the voltmeter would register about 13volts, but would drop out again.

My mate bought me a 70amp alternator to replace the stock 85amp one with and it still wouldn't charge. I jumped the sense wire to the batt terminal on the alternator, and it was working for a bit, but wasn't keeping the battery at full charge. I've got 2 amps, subs etc and 2 headunits running in the car along with the efi so i thought maybe 70amps wasn't enough.
I'm currently running my old 85amp alternator in the car which will charge at 13v once i rev the car over 3500rpm, but every 2 weeks i've got to trickle charge the battery. I've also got a 120AH truck battery in the boot in parallel to supplement it which doesn't seem to get enough charge either.

I've just bought a new 200amp 3 wire alternator off ebay: http://www.ebay.com.au/itm/290604329...84.m1439.l2649

to rule out alternator issues, and my theory is that when I wired all the fuse panel back up, either the field sensing wire, or idiot light wire was not put back on properly.

I've since removed any wires for A/C or courtesy lighting that wasn't being used to tidy up the shitstorm of redundant and duplicate wiring, and may have cut that off in process.

In the engine bay on the wiring harness for the alternator is a 2 pin clip connector, with a thick red wire, and a thinner brown wire.
One I assume is field sensing, the other is idiot light.

What I'm hoping some can, with absolute certainty tell me, is which wire goes where and how to re-run the wires from the alternator to where they need to go.

I've seen posts saying the field sensing wire should be hooked at the end of the power line to something drawing power to detect the voltage at the lowest point to tell the alternator to charge.

I've also seen posts saying the idiot light wire must go through a bulb/resistor to send the right signal to the alternator to turn in on to charge. No-one has mentioned if this is a constant signal or just a burst signal when the ignition is turned as most cars idiot lights turn off after starting.

My firebird as far as I know doesn't have a battery light unless its the |/| light on the dash which i have no clue what it is, but since the rewiring has not come on. Also the gauge panel is the non idiot light version, with volts,oil,water,fuel,tach and speed.

Anyone who can tell me exactly how it works, I'd be greatly appreciative.

Cheers.

 

The two pin connector on your alt is the voltage regulator. pin 1 smaller wire is a key on and off ignition power (should see 12 volts with key on and running). It turns the regulator on and off. The other (pin 2) is battery volts it tells the regulator what the bat volts are. you can run it directly to the battery stud on the back of the alt. if all is good then should charge.

 

So pin 1 doesn't need a resistor or any sort of signal for the alternator, just 12volts from the ignition/accessories rail on the fuse panel?

 

Resistance wire or idiot light key-on to terminal 1 or F (field), and full-time 12V to terminal 2 or S (sense).

 

You can wire it as the diagram shows or just put ignition hot to it if you not going to use a light.

 

Afaik on a 3-wire, the field terminal has to have the idiot light or resistor (electrically equivalent) to limit current and avoid damaging the alt. Should come from a switched 12v source (ie ign on) to avoid a flat battery when engine off.

 

Ok so...

If I run a wire from the accessories rail of the fuse panel, with a 10 Ohm resistor, and then run a wire from the resistor to the field sensing connector on the alternator it will cover both?

If it just needs a 12volt line to the alternator, the resistor won't make a difference.

And if it does need the resistor signal it will work, so both options are covered and it won't cause damage to the alternator correct?

Also if I run the other pin from the alternator to the truck battery in the boot, would that be the best option for keeping both batteries charging at all times?
Or is it better to run it from a brake light or amp or something?

 

Sounds good for the field terminal; get at least a 1W resisrtor. Though if you've got the dash gauge, the factory resistance wire should still be in there somewhere - no go?

For the sense terminal - for simplicity's sake, start by just connecting it to the alt output terminal and see how it goes. I assume you've got fat wires running between batts and alt to keep voltage drops to a min.

 

Yeah I'm not sure about the field sensing wire as it might have been chopped when I removed the tumbleweeds of excess wires when cleaning it all up.

I've read that putting permanent power to the voltage by looping the voltage wire to the +batt terminal measn the alternator is always on and will slowly drain the battery or reduce the life of the alternator, is that true?

Also according to the USPS tracking info the alternator is already in Australia so I should get it tomorrow or the next day.
I've had items come from the same city take longer here :P

 

As per the diagram above, the factory has terminal 2 (sense) hooked to 12v full time, just the field is swit ched. I guess the sense terminal doesnt draw much current, I've never checked.

Back when I still had a 3-wire this is how I had it wired, never had any problems.