Ignition questions

[lazyguy]

My '76 J truck has the prestolite ignition system with the motorcraft alternator and it is not working so well. When I go to start the truck it will just crank and crank and after a couple cycles of this it will start. I have checked the voltage to the coil with the key on and I get 11.8 volts on the first try but if I turn the key on and off again and let it sit for a little it will kick up to about 12.00 volts and then It will finally get spark and fire. It seems to be getting worse. My question is what could be causing this and is there a resistor wire in this ignition system? Some manuals say yes and others don't even mention anything. The reason I mentioned the motorcraft alternator is that it seems to be not charging to its full potential and I thought it might be related. If it doesn't have a resistor wire would using a coil made for a external resistor have something to do with it?

[Ryan]

resistor wire is the brown ni-cad wire coming from the back of the alt and going into the cab. If this wire is cut or shortened, it won't allow the alt to charge properly.

[lazyguy]

i don't have that wire, I just have a red output from the alt to the cab which powers everything, no brown wire and I have a factory service man wiring diagram and I can't find a brown resistor wire anywhere. I'm starting to think that I don't have one. I would just like to fix the low volts to the coil so it sparks its best so I can tune the carb and get a reliable running vehicle.

[Ryan]

Does your alt have an external voltage regulator?

[lazyguy]

yes. I just put a new one in along with an alternator

[Ryan]

that explains it. The ni-cad resistance wire is for the internally voltage-regulated alternators.

[lazyguy]

Why would you even want a resistance wire on the alternator? Shouldn't the internal regulator take care of voltage output? I just seems redundant.

[Ryan]

wait, are you trying to use LOGIC when looking at an AMC design??

The alts on the internal voltage regulated 10 & 12 si alts used a brown ni-cad wire to tell the alt when to charge / not charge.

[lazyguy]

alright

[lazyguy]

figured out the reason it wasn't staying running. Ignition Module took a dump, put a spare one in that I had on the shelf and bam started right up. I also made my own relayed ignition setup to a switch in the dash.

[lazyguy]

So I'm thinking now its time for me to upgrade my ignition system to an HEI or MSD. What would you guys recommend? Are all the HEI you offer the same or do some offer better performance than others?