I have a 1950 3800 with '55 235 that was converted to 12v with an alternator before it came to me, and I'm trying to figure out how it is supposed to be wired to the starting system.
I attached photos of the starter motor, the side stud with the small black wire went to the 12v ignition coil, the larger wires on the switch to the motor came from the battery and the ignition switch as well as what looks like a resistor. I think the ignition switch was bypassed to just need the foot switch to start the motor?
I'm going to rewire the entire truck, but since the system is 12v and not original I want to make sure it is wired correctly, at least the ignition/starter system!
-Starter motor wired directly to battery pos. on the foot switch button -Ignition wired to ignition coil pos. and battery as appropriate -Ignition coil neg. wired to distributor cap post on side and the main wires as appropriate
Hope that made sense! I'm not very familiar with electrical so I hope someone can point me in the right direction or provide a wire diagram applicable to this situation.
The keyed ignition wire should go to one side of a ballast resistor which should have been added when your truck was converted to 12 volt. The other side of the ballast resistor connects to the + side of the coil. The side terminal on the starter also connects to the + side of the coil.
Your coil, even if it is marked 12 volts, is actually 6 volts. The ballast resistor reduces the voltage from 12 to 6 to keep you from burning out your points. The side terminal of the starter connects to the coil so that you have a full 12 volts going to the coil just for starting. When you release the stomp starter, that side terminal disconnects and the coil is powered with the 6 volts from the ballast resistor.
6 volt systems don't need a ballast resistor because, well, they are 6 volts and don't have to be reduced.
There are real 12 volt coils, but you won't (shouldn't) be using one if you are using a points ignition system.
RUN- - - - -do not walk, away from a Pertronix system! If you want an electronic ignition system, use the original equipment GM distributor used on the 230/250/292 engines.
You need a Delco coil marked "12V" on the housing. It operates at approximately 9.5 volts, which is why you need a ballast resistor to drop the current carried by the points during normal running. When a very cold (or hot) engine is being cranked, the load on the starter drops battery voltage to the mid-9V range, which is why the resistor is bypassed during cranking. That's the purpose of the small stud on the side of the stomp start switch. A wire from that terminal to the coil (+) supplies full battery voltage to the coil when the engine is being cranked, then the circuit goes back through the resistor to supply the coil with 9.5 volts or so while the charging system is producing 14+ volts during normal running. Without the resistor, the points will pit and burn very quickly.
The "12 volt coil is actually a 6 volt" myth has been repeated so often that some people believe it. The Delco coil with "12 V" embossed on the can is a 9.5 volt unit which is correct for ALL GM vehicles with a 12 volt point type ignition system. There are two types of coils for GM vehicles- - - - -"Delco" and "Wrong"- - - - -ditto for voltage regulators! Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Jerry, I see a lot of different model # Delco coils offered for sale by the usual suppliers. Will the brand new ones work OK or do I have to track down an older version with "12V" embossed on the housing? Is there a preferred ballast resistor part #?
Use a ballast resistor specified for any GM vehicle produced from about 1955 to the late 1960's. They're all the same. According to Rock Auto, you need a Delco U505 coil and a Standard Motor Products RU10T resistor. The RU10 will also work, but the T series has connectors that resemble the original equipment part if that matters to you. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
