I drive my car every day and no problems with cranking, then I get in my car day before yesterday and it wouldn't start, inside lights come on and you can hear the starting relay trying but no cranking. So first thought, battery, it seems ok but replace it anyway. Still same issue, take the alternator out, it tests fine, so I put in the car and have it tested that way, the guy tells me that its only putting out about 12 volts and it should be around 13.5. I get a new(reman) alternator and still same issue, the dashboard ammeter still is almost touching the redzone. I have hooked up my autotap and the ignition voltage is reading 11.7-12 when its running, which should be 14.5 according to Autotap. Any ideas on where to start looking??

 

Check for corrosion on the battery cables.

 

The connections on the cables look good, also I checked with the voltmeter between the negative terminal of the battery and several ground locations on the engine/alternator and teh resistance is zero which would indicate proper grounding correct?

The voltage across the battery when the car is running is 11.8V and drops a little when I turn on all the accessories. Also the ACV is less than 0.03 volts between negative terminal and the output post of the alternator so that is ok. It appears that the alternator is not charging at all. I read somewhere about the excitor(sp) wire?

 

Ok I cleaned all the ground straps, all the connectors on the left for both the negative and positive terminals but still no change, the car still is running from the battery........

 

The voltage on the exciter wire without running the engine is 11.8V with the battery at 12.2V. Is this the correct voltage on the wire? From reading on this forum I am not supposed to run the alternator without that wire attached?

 

using a ohm meter is useless. ESPECIALLY when the circit is closed. the rigtht way to check if a wire is usable or not is by a method called "voltage drop".

Using MulitMeter reading DCV, put negative on the negative battery terminal. then postiave on the the engine ground and crank the enging over. if you meter reads above .5V you got a problem on that wire. Do the same on the posative leg of the circut.

 

UPDATE:
Well I performed the test as I mentioned above: new pigtail with a 470ohm resistor to a 12 volt source and now the alternator works! However, the dashboard shows also that the alternator is now charging. It was my understanding that the single wire from the alternator feeding into the wiring harness was what gives the voltmeter in the dashboard its reading, which I guess it does not. Now I am up to having to find a bad wire that leads to the alternator, any ideas where to start looking???

 

Use the voltage drop test mentioned above on the wires going to alt. its the most valuable test I ever learned when elextronics are related.

http://en.wikipedia.org/wiki/Voltage_drop

also, figured I would throw this in. dont know if you have it or not. :

(this is for a 95Z28. no one knows what you have without a SIG, please add one. if this is not your year let me know I will get the rite one)

http://www.picvalley.net/v.php?p=u/1196/494374023.JPG

http://www.picvalley.net/v.php?p=u/895/532772949.JPG

 

Kyle,

I got my signature updated, thanks for pointing that out. I have a 96 Z28. Btw, the link to the pictures are not working. I have done the voltage drop and everything is fine when using my jumpered connection. I have been reading the wiring diagram and it shows that the red wire from the alternator goes to the instrument cluster and into a solid state "box" then to a fuse. Have any idea what this solid state box is? Is that a chip on the instrument cluster circuit board? Does anyone have any pictures of the back side of the instrument cluster? Thanks for the help btw Kyle, it is appreciated!!

 

oh, the pictures are just wiring diagrams anyway. it will load the site is just slow but it does not matter since its a 95 and you already have them.

thanks for adding a sig, that helps for sure. and I would like to see that custome fuel pump door man.. lol. jk. :-)

anyway. hmm. all it says is solid state?.. where is that wiring diagram from?

 

I took a picture of the wiring diagram:
www.auctionsilo.com/downloads/P1010975.jpg

It is from Hayes but Chilton lists the same thing.

Unfortunately, I did not take any pictures of the fuel door but if you ever need to do the fuel pump look me up there are some great resources on here to do it right.

 

ok. that is actually the guage itself withing the cluster:

 

ok. you say that you have bypassed the gugage to to full field the altenator and it works.. well the description of operations says that the guage takes part in voltage regulaton. and since you bypased it and it worked good, Im guessing you could have problems up there in the guage.

 

Are you sure? Reason I ask is if I am looking at the diagram below the gauge is actually connected to the power feed of the whole dashboard. Furthermore, the wire in the first diagram is disconnected now and the gauge now reads that the alternator is charging.
www.auctionsilo.com/downloads/P1010979.jpg

 

Thanks for the info Kyle!!! Where are you getting that from if I may ask? I am doing what it says "suitable external resistor to L" and now it works. I did measure 11.8 volts on the wiring harness wire to L but I am wondering if maybe the resistance is too low somehow?