87 GTA 350 with rally gages

I have battery voltage on the battery lug at the back of the alternator, red sense wire is also battery voltage, the middle brown wire is battery voltage with KOEO, the black wire never gets anything.

I have had the alternator tested by two different auto electronic shops, it tested good. with car running DVOM reads battery voltage only, never gets to 13.6+. I have the dash cluster out and have changed all the bulbs just to be safe, but there is no specific battery light bulb. I assume it is the battery icon under the volt gauge that is supposed to light up when KOEO and go out when the car is running, but there is no bulb for this in the back of the dash cluster. before i begin pulling the harness for this from the engine to the firewall can anyone tell me where on the dash cluster I should see the battery light come on at? and what else I should check to find and isolate my problem?

Thanks
RJMcEachern

EDIT: I took the cluster apart and there is no bulb on it for the ignition on ... now removing wiring harness starting from the starter...

 

Here's a diagram for the charging system for your gta. Hope this helps. There should be a charge light somewhere on the cluster plus a volt gauge.

 

Thanks jermdm for the diagram and the reply. I have verified continuity with a DVOM set to tone and I get the tone signal from the wiring plug at the alternator to the c100 connection, I forgot to check resistance on the wire but can do that easily enough first thing this morning. I am now working under the dash to get to c100 inside the firewall and chase from that point. I had the dash cluster out and checked the bulbs, they all work, I even added a couple of additional bulbs to be safe, one is the shift bulb, and the one other, forget which one it is. I even took out the volt/fuel gauge to see if there is a hidden bulb inside of the cluster unit and both are sealed units. there is a bettery icon right below the volt gauge but it does not have a bulb behind it.

One thing is on the diagram it shows the .8 brn wire on the L connection of alternator, I never get power or any reading from this wire, and on my harness it is a black wire, sorry for the long ramble, just trying to give as much info as possible...

RJMcEachern

EDIT: The other bulb added is a yellow idiot light with | / | the forward slash has a circle in the center of it

 

i went out and checked continuity to the upper plugin for the dash cluster, I have continuity and resistance measured 00.00 for the black wire, I am unsure which circuit on the board to check for continuity and resistance

so i have verified up to the dash cluster wiring is good, is this the section that goes off to fuse panel? going to install the gauge cluster and check both sides of gauges fuse...

RJMcEachern

 

I would ck the plugs that conect to the alt itself , sometipes the wire pulls free from the conector . and you cant tell because the insulation looks fine . this happened to me once .

 

i would agree with you, but by checking continuity from the plug at the alternator to the connector in the dash I think I have eliminated the plug at the alternator from the equation... Please let me know if I am missing something and need to perform another check to rule the alternator plug out

RJMcEachern

 

the copper wire it made up of severel strands all twisted together , My problem was only 2-3 strands were still conected at the plug , showing continuity , but the other 18 or so strands were broken off . found out bu pulling the plug and wire , and it streched , not good so I cut the plug off and put 2 wire conectors on ,and pluged them in individually . It was fine after that.

 

ah that is good to know, i will have to check it, i'll have to admit it does look very suspect as the wires are all bent at crazy angles and such, i didn't think the individual wires and connectors would come out?

RJMcEachern

 

I looked at the diagram some more. If the L wire is fine at the alternator, the problem is elsewhere. When the alternator is unplugged, the L wire should show 12v on it which you are not getting. Since you see a battery icon but there isnt a bulb to replace, the bulb probably isnt replaceable. In the diagram, there is a resistor in series with the battery light. That resistor might be bad causing you not to have 12v on the L wire. Other firebird guys might know more about it. I'm not that familar with the firebird clusters.

 

thanks jermdm for the reply, I would agree that the L wire is at issue, I just called autozone and they can order the airtex/wells replacement part number 1P1067 for me, 15 bucks and 3 days wait. I think to be safe I will replace this for that price, but I do not expect it to resolve my issue..

I went out and tested, with the gauge cluster re-installed into dash both sides of the gauges fuse and the L wire and did not get continuity or any measured resistance, The wiring harness is connected back to the firewall but the engine side of the harness is not re-installed, do I need it to be re-installed to check for continuity or resistance? I would think no to this question but unsure where to go from here, I am really beginning to suspect the gauge cluster resistance portion of the circuit and I believe this is inside the gauge itself or on the back of the printed circuit of the cluster...

RJMcEachern

EDIT: The resistors on the back of the printed circuit paper test good, I get continuity and resistance is 00.00, but the gauge itself is a sealed unit and I am unsure how or where to test it, the pink/blk wire in the diagram, I am wondering if the bulb is in the sealed unit of the gauge itself???

took out the sealed unit and it does appear to accurately measure voltage on the gauge itself, I used a 9v battery and the two bolts that mount the gauge, so now to move onto the pink/blk wire

 

It looks like the engine harness doesnt need to be plugged in to test the circuit. Just the C100. The L wire comes straight from the alternator to the C100 connector then to the cluster. No other connectors are involved in the circuit. I guess another thing you can check is see if you have 12v at the cluster connector coming from the fuse at the pin that feeds the light. That way you know you have 12v feeding the circuit up to the cluster.

 

You can also check the resistance of the cluster for the battery icon. With the cluster out, measure the resistance of pin 9 connector 1 to pin 12 connector 2 on the cluster, not the harness. You see this in the diagram. You should have resistance, if not, there is an open in the cluster.

 

the cluster checks out using those connections I get tone and resistance is .005...so onto pink wire now

RJMcEachern

EDIT: The pink/blk wire is fine to the fuse panel from the cluster connector, on the fuse panel there is a one large pink wire feeding power to this section of fuses, so I am going to hook up the alternator and the wiring harness back into the engine compartment and get the cluster back in and see if I get tone or if my break is in either of the cluster connections, maybe a tab isnt making full contact?

 

I now have it all back together, but the wire harness is not installed in engine bay, I am testing the L wire at alternator plug and the pink/black at the gauges fuse on fuse panel to test the whole circuit. I have already ruled out each individual component i think

if anyone knows what the dash light that looks similar to this is for please let me know

|/| with a circle in the center of /

RJMcEachern

EDIT: checked from alternator L wire at plugin to the pink/blk at the gauges fuse and no tone, somewhere I am losing contact on this section of the circuit, seems like it is most likely the dash connector for the cluster it self as these are somewhat rounded to make contact with the printed circuit paper, I am going to try and expand these some to ensure they are making good contact, i also plan on tracing the pink/blk wire back from the fuse panel to the cluster connector..

 

so with all back in and checking from under the dash the back of c1 number 9 to the alt plug in I do not get tone, check each individual component I got tone, when connected together I do not

one thing I have noticed that is different and don't know if it matters is in the diagram it shows the L wire as being brown, mine is black, also on the c1 number 9 it is black and not pink/blk

jermdm can you post a diagram of C1 and C2?

RJMcEachern

 

so i went back and checked and if I jump the top connector 12 and the bottom number 9 i get nothing, if i reverse and do bottom connector 12 and top connector 9 i get tone, so i also checked the gauge again by using a 9v battery and it works, it reads just a hair above 8.5v, so it has to be circuit paper on back of gauge cluster??? I am assuming the C2 is at the top of the cluster and the C1 is at the bottom of the cluster?

RJMcEachern

EDIT: My C2 number 12 is a dead end circuit, goes to nowhere, but looks like it should jump with a resistor to number 9, but it is blank, i'll try to get a photo and show these details I am speaking of. 12 on C2 is where my wire is coming in and i get tone on it

 

I've studied the circuit board on your cluster. I see that pin 12 on connector 2 is a road to nowhere. I have a diagram for a volt gauge that has a black wire going to the volt gauge and it shows it on pin 12 on C1. In my diagrams, I dont see a black wire on the alternator. Here are some diagrams that I do have. I'm guessing that you dont have a charge light indicator since pin 12 on C2 goes nowhere and thats where the alternator wire is going to control the light. Your car just uses the volt gauge for charging indication. In the diagram, the volt gauge uses pin 12 on C1 which is ground. So the volt gauge diagram seems to match what you have and all is working properly. Since you are having a battery charging problem, I would be looking at the charge wire from the alternator to the battery for high resistance or the other 12v supply wires S and F on the alternator for high resistance. With the alternator connector plugged in, back probe terminals S and F and see if you have 12v with the engine running.

 

yea it is very weird isn't it? i really think tomorrow first thing I am going to wire a 194 bulb inline to a KOEO power source to the L wire on alternator and start the car and see if I get voltage above 12.8v at the battery, battery lug, if so I think I will wire a gauge pod volt gauge on the A pillar and be done with it, tired of trying to fix the default factory wire harness... thoughts?

RJMcEachern

 

Not Forsure if you read my post since I've edited it. I wouldnt worry about the 194 bulb thing. The L wire doesnt have anything to do with the alternator charging. It just controls the charge light which your cluster doesnt have. I would start checking the power wires at the alternator for resistance since your original concern is the alternator isnt charging.

 

i will try to get out this week and get those measurements

RJMcEachern

EDIT: too cold outside to get these readings, weather is expected to be better later in the week, will have to check then..