I am wondering why on a typical 80's style GM 3 wire alternator, 1 wire coming out of the side plug is grounded, and the other is not there. can anyone tell me if they have seen this?
One wire feeds the idiot light. The other wire goes to the switched side of the ignition switch to provide a reference voltage for the voltage regulator inside the alt. Some folks wire that second wire directly to the alternator 'B' (BATTERY) terminal and while this works it is not correct and will lead to chronically undercharging the battery. The reason for this is that the regulator is calibrated for the slight voltage drop that occurs over a several foot long, skinny piece of wire. Wiring it directly to the alternator output terminal reduces this voltage drop, so the reference signal is higher, and the regulator thinks the battery is fully charged when ther really is a ways to go.
/\ /\ /\ Interesting, I've never heard this. I just jumped mine over on my daily. Is it something that you recommend I change?
Technically the sense wire should hook somewhere in the harness a little more remote than the back of the alt., but I have seen plenty of them just looped back to the alt. and keep the battery topped up just fine.
Thanks, I have never seen this before, I just bought the truck, and is my new project. I am installing a new wire harness, and while the truck now runs fine ( after engine work ) I just decided to look into this strange wire route.
I've got three cars wired with the jumper to make them a 1 wire. One has been this way for 7 years, with no problems, and it's my daily driver. The others are 4 years and one year, and no problems. Not sure why some people seem to have so many problems with the 1 wire jumper setup.
SO let me ask.... Is the 1 wire from the plug on the side going to - (neg) on the battery OK? I have never seen this, but the engine runs, battery charges ect.
No. If it truly is an internally regulated Delco (10SI or 12SI) then the regulator voltage sense lead (pin #2) should "ideally" go directly to the + battery post, and the #1 lead is used for the idiot light. Neither of them should be connected to the negative side of the battery, unless you have one of those rare positive ground Delco's. A lot of the one wire conversions are done by simply connecting the sense lead to the large output post. It usually works out OK, but the alternator does not see the actual voltage at the battery, so there is a risk of having a battery that never gets fully charged. I prefer to wire them the way GM/Delco designed them to work.
If your alternator is a 10 or 12 SI, the simple diagram below is a correct way to (3) wire it. A diode can be used in place of, or in parallel, with the lamp. A ground (4th) wire can also be run from the threaded boss on the back of the case, and is a good idea, imo.
Car? Year? Battery positive or negative ground? None of the terminals should be grounded. Only a service lug that goes to the case might be grounded. Big lug goes directly to battery+ One side lug goes to battery + (not to big lug) Other side lug goes to switched battery (Accessory position of ignition switch) You sure that the (other side lug, that you say is grounded) is not wired already to provide switched 12v to it. But when you read it with ohm meter the it shows a low resistance. A picture of what you have might help too.
The last connection you referenced is pin #1, and needs to have an idiot light, resistor, or diode in it. Without one of these items in series you will likely not be able to shut off the car.
How well a single wire alternator will work depends on the load, circuit paths and wire sizes in those paths. If the wiring is sized large enough for the load, you'll probably be ok. The OEMs use the smallest sizes possible, so the three wire is better able to compensate for that.
If you wire #1 to accessory terminal of ignition switch will work too. It won't work with ignition terminal of ignition switch.
Did not know that as I do have mine wired that way,it will give me something to do this weekend and run a wire to the solenoid.
Actually the first time I ever saw one wired back to the output stud was a 1976 Chevy 2 1/2 ton truck, I was repairing some shorted wiring and discovered it wired that way from the factory. Kind of gave me the idea that GM probably thought it was a good enough alternative way to wire one, have done several myself and advised others over the yrs., and to my knowledge none of them had any problems keeping the battery topped up.
I am at the point, I am going to double check the Alt output, The wire kit I bought has new alt wires, which I will install. I may take the alt apart to make sure the guy before me didn't do something, this after I check to see whether its even charging. Thanks
To clarify, it WON'T work off ignition terminal if it does not have resistor, diode, or idiot lamp in series with the field terminal.
Many jump it right at the alternator. That works, but it is not right. The risk is that you chronically undercharge the battery. Think about it: would the factory have installed that extra couple of feet of wire if all they needed was to jumper the alternator? For the level of technological sophistication designed into these particular alternators, the 100% solution is to install it as described.
What is wild about this, I unplugged the side plug, cut the wire off the Neg battery lead and used the new wire from the kit. So 1 wire with a fuseable link connects to the solenoid, same side as battery. Then I plugged in the new plug, the red wire connects to the single pole out of the back of the alt ( same as the wire to the solenoid) then the other wire goes through the harness into the cab and connects to the wire in the harness. The alt still works after having the 1 wire grounded..... That amaizes me. 13.8 volts. I was sure I was gonna need a new alt.
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