Hello all, I have a 1956 F250 w/272 and recently did a GM three wire conversion and have a question for anyone who may have had the same problem. I have alternator wired correctly and it still behaves like a one wire conversion. I have attached the exciter wire (with diode) to the coil, ign switch and tried wiring it into the gen light lead. The gen light stays on and the engine needs to be reved up before it starts to charge. I am getting power to the plug and when the plug is disconnected it won't charge at all. I have tried two different alternators (rebuilds) and still not working correctly. Does anyone have any suggestions? Thanks Tom
As I recall from 50 years ago, you need to put a resistor across the gen light to keep it from staying lit.
A lot of those GM alternators have to be revved up before they start charging. I have three cars I put them on and they all do the same thing but at different speeds. My cars are too old for a red light, though. I wouldn't worry about it to much. If the exciter wire sends voltage to the alternator and keeps it there, but turns it off when the engine is turned off your okay. Try running the exciter lead direct to the hot wire on the coil. You need a resistance in the wire and a small light bulb (like the idiot light ) will do the trick. My shriveled up old brain doesn't remember if the light turns on or off when charging, though. I don't understand why you would need a diode ? I've started using all one wire setups on my own cars. Much easier.
Thank you all, I'll try the resistor. Aside from this issue it works and looks great. Thanks again Tom
I have 3 wire 10si’s on all my cars and the ones that don’t have a stock charge light I added a light. Some of the cars take a little more then cold idle rpms to turn off the light.
I've wired up a lot of three wire alternators using the diode and have never used a charge light. I save every wire up a Delco 10 SI or 12 SI Alternator in something it didn't come in here. Photobucket I haven't got any diagrams for the newer ones yet but there are some pigtails out there to connect them where a 10 SI went. For the diode installed impaired this pigtail you can get from a guy in El Paso is pretty handy for the price. Ebay number 201247906131 I got one a while back and for the price it is hard to convince yourself to run all over town looking for diode even though the diodes are cheap.
The leads on the "gen" light are as follows: one to accy, not ign, one to the white lead on the alt plug. When the key is on, engine not running the circuit is grounded through the alt and the light lights. When the engine is running, the alt is excited (regulator turned on) both of the leads are then +, the light goes out (because the ground is lost). If the alt / regulator fails, the ground is restored and the gen light lights again. Does your gen light have two leads? it needs to be isolated from ground to work with a SI style alternator. My Falcon was wired this way and worked perfectly. Good Luck. http://madelectrical.com/electricaltech/onewire-threewire.shtml
The number 2 post on the flat plug, the one that everyone tells you to hook to the 12 volt + on the alternator is the load sensing wire. It should be connected to the junction block where all of the load, or accessories are connected, on older cars it is usually the ammeter or the headlight switch. This tells the alternator to up the charge rate when there is a large draw. The alternator does not work as well if the wire is jumped at the alternator to 12V.
You need to clarify that that diagram is for a CS 30 alternator and not the 10 or 12 SI under discussion in this thread. Technical Articles - GM Upgrade to a CS Alternator (bzerob.com) [/QUOTE] This is the correct wiring for a 10 or 12 SI with a diode or resistor. t
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