Finally got through to FiTech tech line, they said ECU needs 12V, lower won't work.
When I explained problem with Mopar ignition not having these 2 simultaneously, his response was , "you need to find a source".

Sounds like John's relay may do the trick.
Only concern, if the ECU voltage is so critical, what about the relay switching time between engine crank and run?
Won't there be a few msec of dead time as the relay switches between the 2 sources?

yes John's Relay diagram will do the job JUST if the relay really don't work with low voltage either... if does, will need a diode coming out from ballast or just right before the splice to feed the 86 prong to keep safe from the low voltage triggering the relay

Don't worry about ECU... is designed to work on the way it is and it has being in that way since ever

the death time between the switching is not critical, and is in fact unnapreciable. If was important, system wouldn't work

I was talking about the ECU in the FiTech throttle body.
Really surprised they don't have a suggested implementation for this.
Hopefully they have MANY Mopar's using their system.

ok, I don't think will be critical either... MSD ( even digital units ) works the same on same Mopars system. I'm pretty sure the points inside meets at certain point. I actually never have advertised a death point when cranking. You can see that while you are starting up your car at brake light on cluster. The RUN and START switching is noticeable on that light, when cranking the brake light dims a bit because is getting feedback from the ign2 circuit through the ballast up to the ign1 circuit

wrong... brown circuit is allways hot while in RUN, NOT COMING FROM IGN SWITCH but from ballast, so it gets reduced voltage. Thats how the coil is allways hot too

check it and think on it

He can't remove ballast &/or splice brown and blue circuits together using stock system ignition, becauise will overheat the coil [/quote


Check the factory service manual. I've done many. Dark blue wire from the ignition switch is hot in Ignition (key on) but dead in crank. The brown wire from the ignition switch feeds the ballast with 12 volts in crank only (dead in ignition position).The original intention was to bypass the ballast in crank for full ignition feed voltage to the coil in crank only (brown wire), then to ballast voltage (dark blue wire to the positive side of the coil. That's why the brown wire is on the output side of the ballast, it bypasses it.
Doug

Thanks, this threads happens to be at the perfect time for me.....

Correct, brown wire bypasses the ballast during cranking saving the low voltage for a stronger start up, then when ign switch returns to RUN, the brown wire is not anymore feeded by ign switch BUT keeps linked to the ign circuit through the ballast buddy!! So KEEPS HOT unless you disconect it from ballast, which is not posible because is spliced into the same coil wire and if you disconect it, will stall the engine

TEST IT! Start up the engine and test for voltage at ign switch brown wire and will get a low voltage power there. Is te same power the coil is getting!

I can't believe this si being really discussed! Its so clear!

;quote]
I can't believe this si being really discussed! Its so clear! [/quote]
Lets try this again

I thought it was clear to me as well until i reread the entire post, my mistake. The fact that the stock style box is being used with an aftermarket FI system would indeed need the ballast. My incorrect assumption is that it was using an aftermarket ignition box. In this case it would be best served by using the relay as John suggested. With an aftermarket ignition ignition the wiring I described would be all that is necesary.

[quote] BUT keeps linked to the ign circuit through the ballast
buddy!! So KEEPS HOT unless you disconect it from ballast,



[quote] brown wire bypasses the ballast during cranking saving the low voltage for a stronger start.

The brown bypasses for MORE voltage to the coil during crank.


I hope this clears it up.
Doug

yes the brown wire bypasses the ballast for FULL batt power at coil, full 12 volts from ign switch through Ign 2 circuit instead the reduced voltage coming from Ballast from Ign 1 in RUN.

BUT the brown wire while is connected to the ballast is ALLWAYS HOT... no matter if not being feeded from Ign 2 at ign switch. The ballast IS A SPLICE that links both circuits, just a diff voltage rates on each side due the Ballast propperties

isn't the coil wire allways hot ? full power while cranking from ign 2 or reduced voltage from Ign 1 through the ballast is allways hot. If wasn't on that way, the engine wouldn't work, that's a fact... or isn't a fact ?

If the Ign 2 wire coming from the ign switch is SPLICED INTO THE BALLAST end to feed the coil wire at full power when cranking ( bypassing the ballast )... doens't mean that THE WIRE coming from the ign switch will be ALSO hot no matter if is not cranking BECAUSE IS ON THE SAME LINE THE COIL IS BEING FEEDED AT ANY IGN SWITCH STAGE ?

so, the ign 2 circuit is ALLWAYS HOT just like THE COIL, on same voltage rates than the COIL on any of the stages. There is no way to cut the power on ign 2 circuit wire between ballast and ign switch because is spliced on the same line than the coil is being feeded!!!!! The ign switch is just selecting what voltage rate will source the coil... full while cranking, or reduced at run because that source is before the ballast.

if the Relay suggested to be used to feed 12 volts to the EFI, is able to be activated at 86 prong at the reduced voltage the coil is getting, THEN the 87 prong will be allways closed to the 30 prong AT THE REDUCED VOLTAGE TOO.

what we don't know is IF the relay actually will respond or not to the low voltage rate.

IF the relay reacts to the low voltage input at the 86 prong, THEN a diode will be required to be sure the 86 prong just will react at the bypass step coming from the ign switch on ign 2, and not react to the low voltage rate being feeded back from the ballast end.

is clear now ?

I don't know how explain it clearer if is not now

If the relay doens't respond to the low voltage rate, then won't be a problem... so we need to figure it out.

Need to note the low voltage rate coming from ballast is not a constant and changes with temperature and load going through... so teh relay COULD be responding sometimes yes and sometimes not.

conclusion... IMHO, I will add a diode on the ballast output to the ign 2 circuit ( anywhere between the ballast and the splice to feed 86 prong, BUT NOT between the splice and the 86 prong )

It is to the rest of us.
Doug

Unfortunately it'll be a little while before I can give the relay a try.
I need to fix a leak in the return line, and I have to put that on hold because I have to go out of town for work.

Any idea what the typical voltage drop across the ballast resistor is?

4.5 to 9 volts is the usual... changes with the load and temp

If concerned about feedback from the ballast, add a diode to the IGN2 circuit but a diode connecting the IGN2 to the IGN1 would provide a constant 12V source without the need for a relay.

As mentioned, a diode should do the trick without the need of a relay. I don't run the stock style ignition (with ballast resistor), so I just connect both wires together, and use an aftermarket CD ignition box.

Eeehm... if splice both without the relay, will be bypassing the ballast even with the diode

And have done it successfully several times, including on my 38 with a GM column/switch, and Mopar electronic ignition with ballast. UHH its be in place over 40 years,

Well, is true, but not on the position its on the diagram. Will need to be making the brigde or "jumper" between both circuits just right where the relay is, but diode triangle pointing out to the ign 1 circuit... then take the signal to the EFI from the ign 1 ( RUN ) circuit.

If want to use a Relay, should be just like the upgraded diagram by John.

That Diode in place of the relay should in fact give more power to the ignition ECU while cranking, and won't make dim out the brake light in cluster.

Sorry the multiple post but think on details after every post.

The link with the diode couldn't affect the ballast performance adding extra load or circuits to the coil circuit ( by the default on the jumper ) while in Run ?

Same problem with Gen3 Hemi swaps using Hotwire harness. Easiest solution is to wire in a push button start using low amp 12v push button to trigger starter relay. Turn ignition to run, which will power up the EFI then push button to start. Done.