gliderdad

Hey everyone...
Ok ..so the '87 is starting to come together.
Got everything put back together in the interior and fired it up to drive around. My voltmeter read 11.2 at the start and after driving 3 blocks dropped to 10.2.
Got the car home and pulled the battery(1 month old) and the alternator and took them down to be tested. Both tested ok...so I took them to another shop and had them tested...same results. I called another car guy and he said there is a possibility that the regulator in the alternator could be bad and the alternator could still be testing OK.
I installed a NEW alternator and get the same results.
The drain only occurs when the car is running. You can put a voltmeter on the alternator and or battery and watch the volts slowly count down.
Any ideas on why the alternator will not charge the battery, and why I am not getting a reading any higher than 11.3 volts?

adtbrown

Either a ground or a fusible link between the battery and the alt. 11.3 is about right for a battery that's not getting any charge at all.

65Z01

At the Alt there is a 3-wire connector from the Regulator:
-Dk BLu -> coolant fans
-Brn -> charge indicator
-Red -> #1 fusible link -> Jump Start Junction Block

There is a single wire from the Alt Diode Bridge:
-Red -> #3 fusible link -> Jump Start Junction Block

From the Jump Start Junction Block:
-Red -> Battery +terminal

You might check all connections and the two fusible links.
My bet is on a bad fusible link or connection between the Regulator and the Cold Start Junction Block.

For this kind of work the FSM Electrical suppliment is indispensable.

BTW, if you need to replace a fusible link the wire size is stamped on the jacket but you must cut into the jacket to check type of link. If the problem is with the #1 fusible link it should be AWG 16 wire size with a Rust jacket.

AGENT 86

If there is no voltage on the sensing wire, the alternator will not turn on.
With key on, do you have voltage on all 3 alternator terminals ?

gliderdad

Thanks for the info..

I will check those tonight after work..

Just out of curiosity..what would cause the fusible link to blow between the alternator and the junction block if the alternator was good?

I did lose the fusible link supplying fan power..but that was due to a bad fan motor.

Also, is there a cover that is supposed to be over the junction block?

SunCr

Touching the charge wire to any ground installing the Alternator with battery connected works for me - but there's usually a pretty good puff of smoke and alot of sizzle as the fusible link melts.

93Rubie

Always a PITA to get that smoke back into the wire too...

coupeguy2001

a low battery will allow the fusible link to get hot after a while and pop. it takes an alternator about 30 minutes to get a low battery up to charge.

I went with a 92 LT-1 alternator. charges better at idle, and is 25 amps bigger and just plugs in and bolts up.

Anyway, jumper the battery stud on the alternator (after you determine it has 12 volts) to each of the other little terminals in the plug on the alternator, and if your alternator starts working, it will lug the engine for a little bit until the Idle Air control valve raises the idle back up.

gliderdad

Ok...
Here are the results with the key on and off and the battery itself reading 11.7v and the 3 wire connector unplugged from the alternator:
At the Alt there is a 3-wire connector from the Regulator:
-Dk BLu -> coolant fans=11.7v
-Brn -> charge indicator=0.56v -Red -> #1 fusible link -> Jump Start Junction Block=11.7v

There is a single wire from the Alt Diode Bridge:
-Red -> #3 fusible link -> Jump Start Junction Block=11.7v

From the Jump Start Junction Block:
-Red -> Battery +terminal=11.7v

Ok...so with this info I am assuming that the brown wire is supposed to show the same voltage as the blue and red wires on the connector, as well as the 10 gauge wire on the alternator stud?

gliderdad

something else I found when testing.

There is a green w/white stripe wire going to a fan sensor? between cylinders #1 and #3. I have continuity between this wire and the blue wire on the alternator plug. I also have power to the green wire...is this right?

I checked ALL of the wires and fusible links at the terminal block...all tested OK. Still no power to the brown wire.

65Z01 you said that the brown wire was for "charge indicator"?

Are you referring to the voltmeter in the dash...or something else?

I really appreciate the responses...

Cliff Harris

The green wire with white stripe goes to the auxiliary cooling fan temperature switch. It will have about 12 volts on it until the switch grounds it to turn on the fan. You can turn on the auxiliary fan and its relay by shorting this wire to ground.

gliderdad

I pulled all of the fusible links from the terminal block and checked continuity of each one. All checked out ok..I even wiggled the heck out of 'em while checking, just in case there was a break in them.

I charged the battery overnight ...again...and got it to read 12.5 volts.

I hooked the battery back up and got 12.5 v at the main lug on the alternator as well as 12.5 at the red and blue wire on the connector, but got only 0.51v at the brown wire..with the key on. The little red battery is not lit up on the information module. From what I am seeing, the brown wire is supposed to light up the battery icon if there is a charging problem...right?

Again the alternator is a new Delco and the battery is only 1 mo. old.
Both checked out OK when tested at the parts store.

this is driving me nuts!!!

Coupe guy 2001..You said to try the below jumper method...Is this a permanent solution? What does the jumper do?


Anyway, jumper the battery stud on the alternator (after you determine it has 12 volts) to each of the other little terminals in the plug on the alternator, and if your alternator starts working, it will lug the engine for a little bit until the Idle Air control valve raises the idle back up. [/B]

Hooked on Vettes

Your gauges fuse is blown in the fuse panel or the charge indicator bulb in
the driver info center is blown. That's where 12 volts to the Brown wire comes from
when the ignition switch is in run, start or bulb test.

Bulb test is when you turn and hold the ignition switch right before the
start position.

65Z01

As mentioned the Brn wire goes to the Charge Indicator (in the Telltale Assembly) and a Pnk/Blk wire from that bulb toes to the Gauges Fuse.

I would like to see what is the voltage reading on the Red at the 3-wire connector at the Alt.
Also what is the voltage on the thick Red wire at the screw on the Alt.

If either fusible link is blown it's possible to read the 11.7 Vdc at the junction block but not at the terminal on the Alt. Even though you pulled and Ohm'd each link it wouldn't hurt to test the voltages indicated above. If there are connectors between those links and the alt, it's possible a connector is bad.

If those all check out OK I have to think the Alt is faulty. When it is tested is the test done under load?

gliderdad

HOV...thanks a ton!!!
The fuse was blown..and the bulb test was interesting...(might want to grab a beverage for this one)
I changed the fuse..and still nothing. I had my test light jammed in the alternator connector at the brown wire and the bulb for the battery was lit..but very dim. My test light was lit up bright so I thought it was pulling power from the battery bulb ..I pulled the test light out and the battery bulb went out completely. I still had over 12v showing at the connector so I thought maybe I had the a short somewhere else.
I had removed the radio to find mouse chewed wires...whole nuther thread about that..and thought I would check one more time to see if I pinched something on the reinstall. I found one more wire that was chewed on. It was the black w/ white going to my heater control switch. I repaired it, hooked the battery back up and my voltmeter was showing 13.7 volts. I started the car and the voltmeter showed 13.9-14.1 volts. I think the alternator is charging my battery now but I still do not have the battery light on the info panel when I turn the key on. This is the goofiest electrical thing I have ever experienced.
I'm happy that it is charging but I feel I am getting set upfor a big let down, cuz the battery light still does nt come on. I think its working, but I cannot stand not knowing the "why" on this one.

OK I guess that was 2 beverages...Anyone want a shot at this one?

Hooked on Vettes

If you've had rodents in the car no telling what other problems you
may find.

To verify the charging bulb circuit works, unplug the connector
from the alternator. Turn the ignition On. Ground the Brown wire
to the negative battery terminal.

The bulb should light with normal brightness.

You did say the Dark Blue wire at the plug has 12 volts on it when the ignition
is On?

Turn the ignition Off. Plug the connector back in the alternator and turn the ignition
On. If the bulb no longer lights or is dim, either the alternator regulator is
bad or the alternator has a bad ground. The ground for the alternator is the case.

Verify the negative battery cable to the engine block is making good contact.
Also if the alternator bracket or alternator has been painted or powder coated
it could cause high resistance from the alternator case to the engine block.

gliderdad

HOV...You cracked the code!!!!
Thanks...I did not know how to force the light on.
It worked great!!!
I must have bent the brown wire terminal in the connector...I pushed it back after the test and everything works as it should.
Now on to the body work....

Hot Rod Roy

It's always a good idea to have a separate ground wire from the alternator case to a good chassis ground.