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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hey i have a 92 v6 RS, im not getting charging voltage, even if i increase rpms the voltage doesnt change.
i checked for voltage on the red wire at the alternator it has 12v, the Brown has 12v and i took it off and got it bench tested 3 times it passed every time, what can i check now? is the black a ground wire?
Is the battery discharging or dying on you? What are you getting at the positive battery and red, black, and brown when it is running? The black goes to the positive side of the battery, should not be a ground.
All 3 wires go to a 12V source. Red, to battery (at the starter). Black is the voltage sense wire that goes to a main distribution point (sensing actual system voltage under load and adjusting alt output to maintain proper voltage AT POINT OF ACTUAL LOAD). Brown is ultimately powered by the ignition switch to excite the field coil in the alternator and begin the charging process (notice it says "hot in run" on the diagram). It's actually only needed once at startup to begin the charging process, but is left hot any time the key is in the RUN position. After that the field coil in the alternator is self-exciting and will keep supplying voltage until the next time you shut down the engine.
Now, if that brown wire is NEVER supplied with 12V, the alternator will sit there like a bump on a log, spinning, spinning, but never charge, no matter how much you rev the engine.
Easy to test for. Check to see if the brown wire is getting 12V with the key in the run position.
There are no external grounds on the alternator- they are all internal to the unit and ground through the body of the alternator itself.
plot twist: red and brown have 12v at the alternator, but the black wire didnt have a reading, do you happen to know location of the junction block? also i just put a new battery in it.
there are 2 wires in the plug: the tan one goes to the ignition switch as already pointed out, and the other wire can just be looped to the terminal on the back of the alternator, which has a cable on it that feeds directly to the battery.. GM liked to use way too much wire for simple things sometimes, and the third gen Camaro is one of those cars where they used too much wire in the charging circuit...
Or you could just trace it back and figure out why it's not connected to anything (you might find other wiring issues that need to be addressed while you're at it!). Remember the point of having that wire is to read voltage AT THE POINT OF USE, which may be slightly different than what it is at the alternator post.
it works just fine at the post on the alternator, which should be hooked directly to the battery (the ultimate "point of use) with a big cable... GM even did it this way on some cars in the 80's..
Yeah, I agree. Tractors that use SI-series alternators often have the voltage sense wire hooked directly to the output terminal of the alternator for simplicity. The problem with doing it this way on cars is: 1. GM uses maybe a 10 ga. wire off the back of the alternator's main post, which is pretty marginal when you're under strong load with an 80+ Amp alternator and 2. The wires on a car are much longer, generally, than a tractor so more chance for voltage drop across them.
If it was me, I'd want to figure out where that wire ended up just out of curiosity, and in case somebody went hacking other things in the general vicinity. Really that second reason would be what would probably drive me to trace it back. I find it difficult to walk away from a good mystery. But you're right- it WILL work the way you described.
Hey just posting a quick update, the bat post (black wire) had 12v supply, s post (red wire) had 12v supply, the f post (brown... looks black) did not. anyway i do continuity checks from it back to the coolant fan relay, and c100 firewall terminal connector all checks out, check for voltage at c100, none. so i trace wires back to fuse panel and the fuse connectors are dead, i cut the power supply wire, i assume goes to ignition switch and the fuse connectors are live... im thinking in between the fuse panel and ignition switch the wire was grounding out somewhere (probably inside the steering column, the vats wires where broken inside and i bypassed vats after some intense digging. but long story short i just have one side of the fuse disconnected and the other going to the regular wiring (relay/post f). and it seems to be charging fine around 13-14v.
also for anyone thats wondering where the junction block part of this circuit is, here's a pic.
I think I followed that. Sounds like it's the field coil "excite" wire that's not sending 12V to the alt. in the "run" position of the key (that's the ONLY position it should be sending 12V down that wire).
Whatever you do to hook that wire up, do NOT hook it to a battery-hot source. It's ONLY supposed to be powered when the motor is running. You'll drain the battery if it's powered all the time. Might damage the alternator over the long term, too.
WORST CASE SCENARIO, run a fresh home run back to a terminal in the fuse box labeled "run".
When you said your car was an 'RS' I assumed Camaro. Clearly that's a Firebird and yes, that's where the main junction point is on a 3rd gen Firebird- behind the pass. headlight.
08-01-2015, 07:08 PM
