Please help: Smoking 308GT4 ballast resistor !

See here for all the tech info you could want on the dinoplex system, some of the above diagrams seem to be adaptations of this.

Magneti Marelli Dinoplex Repair and Restoration Documents

didn't want this link to get lost in a long post so it's separate for those who may refer back in the future.

 

this is on capacitors and points and the circuit layout.

Keeping the ignition circuit from broadcasting is only one function of a condenser in an ignition circuit. The other is making the points last longer. A LOT longer.

Without a condenser, metal will migrate from one point to the other until they're unusable. With a condenser exactly matched to the size of the coil (capacitance = inductance) there will be no metal transfer. Too much capacitance and the metal will move the other way.

You can never exactly balance the two, so all you're really doing is GREATLY slowing down the transfer. When the points open, current stops flowing. Well current doesn't stop flowing, so, without a condenser it will make a nice big arc --- which carries the metal from one point to the other. With a condenser, that "arc" essentially gets shorted out. It gives it a place to go. that's due to the BEMF of the coil, magnetic fields don't switch on/off.

Typically an ignition condenser has one wire and the case is grounded, a 2-wire condenser is actually two capacitors in a single case, for a dual-point ignition or if they simply ran a second lead rather than using the case for ground.

the altered diagram with the removed R2 points has removed the capacitor from the charging circuit that is used to help save the points and also improve the pulse shape. recall the BEMF that charged the condenser, well that charge is now used to induce the next pulse when the circuit is closed. If you look at the charge flow from the electron view vs the conventional it tends to make a bit more sense. negative to positive btw, for the non EE guys.

 

Call me insane,

but just buy new points, new condensers (they are cheap, they match Fiat parts if I recall), install them, set them, and set the wiring up properly as per the provided diagrams. You can experiment to find the cause of the hot resistor, but:

1 -the resistor is hot bc it is getting too much current flow for some reason
2 -the wiring is clearly incorrect and non-original*

Maybe throw in some new coils at the same time.

I too want to understand exactly what's going on, but the real answer is to simply put the system back to a correct condition. Hopefully you can source some properly color coded wires, so that everything isn't red. The energy required to figure out what somene else did, who used non-stock colors and wires and left you no diagram, will be far more than the energy required to put the system back to stock. If you were paying me by the hour, or it was my GT4 that had smoke coming from the engine bay...

Now, you'll have to decide on the value of having two sets of points, and if you want to wire them up properly using the correct off-idle switch to shuttle between them, but that's a totally different philosophical discussion.

Another solution is to install a Pertronix - it'll keep your car looking original but work much better than points. It'll still require resetting some wiring to stock, but then adding the pertronix units instead of setting up 4 sets of points.

Jonathan
The Fiat RN
Denver, CO


*it mostly works, but that doesn't mean it is correct!

 

Yes, that is the shielded factory wire connecting the R2 terminals on both distributors. It can be safely removed from your setup as you don't have the microswitch in place anymore.

With the original factory wiring, there would have been a similar wire coming from the microswitch and going to the R2 terminal of the distributor serving bank 5-8.

 

this looks familiar

 

First of all, the 1975 308 GT4 does not have a Dinoplex ignition. It has 2 Marelli type 159 distributors. Ignore all the comments about the Dinoplex.

I am unclear about that wire connected to the case of the condensor, but if it is connected to the case it's connected to ground. If you've got B+ connected to one side of the resistor and ground to the other side smoke will result.

I agree with the suggestions in the following post, but I'd like to know what Fiat points cross reference to the points in the 159, which, as I recall cost about $65 each (4 required, can get by with 2 if the R2 set is disconnected). Here are the Ferrari part numbers I have for those points:
71 007 106
71 007 107

If FiatRN has Cheaper Fiat cross references I'd like to hear about them.

 

I'm very aware of that, some of the posted diagrams are adaptations of the Dinoplex ones, Ferrari was famous for this type of "sharing" hence why I posted the GT4 one that's different and correct (mostly, it is Ferrari).

I'm short on time at the moment but I'll post up hopefully two schematics late tonight, one for the R1 & R2 and one with just the R1.

 

That hack retards your ignition timing permanently, you should definitely remove it. Please see the chart in post#14 as a reference how your final wiring should look like.

 

Thats what I suggested in post #23. But I have to say I doubted my own post because this would cause one bank not to fire at all. So why both banks were working is a bit of a mystery!

 

Looking at the wiring diagrams in this thread I notice that some have the ballast resistors upstream of the coils, and others have them downstream. It doesn't seem like it should make a difference which way they're connected, right? Someone must have rewired mine because they're upstream in my NA 75 GT4 unlike what's in the manual.

 

The corrext position of a ballast resistor would be between the coil plus terminal and the iginition feed, so they can be directly fed by the starter actuator wire for more spark output while turning the starter.

 

Right, but I guess it wouldn't matter in the 75's w/o the 12V feed at startup

 

Correct, but you could always retrofit the relay for better starting.

 

Put electronic ignition on it, and stop trying to fix something that has -literally- been obsolete for 40 years.