12v Source under key on and cranking?

[68CoronetRT]

Wondering if anyone knows why I'm not seeing 12v under cranking? Using the Brown/Blue wire tied together for a 12v source with key on and cranking, but it drops down to 10.2v under cranking.

Is there any other source for a constant 12v under cranking? Or is it time to just wire in a switch off the battery or something?

[Nacho-RT74]

ok... several ways to do it... but need to know what's for... and what ign system will you use or are using

if is just a trigger on signal, several devices ( such as MSD ) are able to be activated at low voltage rates since is just a trigger, not a power source.

some other devices needs a full 12 volts signal no matter if just a trigger

sooo, be sure on the need for a 12 volts signal for triggering on ( or not ) by the manufacturer

so to give you a better response, give us the full info on what you want to do or what do you want to connect

[68CoronetRT]

Trying to make a Holley Sniper EFI fire. The switched 12v power wire needs to see a minimum of 10.8v under cranking. Currently my 1 wire that I have everything else hooked up to only pulls 10.2v.

What about just wiring my MSD box, Holley EFI, Holley Dist(requires a 12v cranking signal as well) all onto a relay? Maybe that's too much voltage after its running since it's pulling off the battery tap at that point?

I believe all 3 are just triggers to fire up another relay which then gets its full power from the battery connection. If that's the case then why would it need to see 10.8v? Really any voltage should let it fire.

Maybe I should actually just wire it all up and give it a try and see what happens, and if no spark, then go in and do this wiring.

[Nacho-RT74]

ok... let see.

the deal on Mopar stock ignition system is just the double ign wiring system to be able to bypass the ballast resistor during cranking ( called ign 2 )  for full batt voltage at coil + lead... while this happens the ign 1 or "run circuit" is getting back the reduced voltage through the ballast. This voltage uses to be anywhere between 4.5 and 9 or 10 volts depending on the load going thorught the ballast and the engine temp.

Once engine started up and ign switch is returned to RUN position, the ign 1 is the circuit feeding everything from ign switch getting full 12 volts, including coil BUT at reduced voltage being the voltage to coil is now running through the ballast ( once again, anywhere between 4.5 and 9 or 10 volts ).

MSD instructions ( modules, not RTR dist ) states the signal to trigger is enough to be used the same that it sources the coil, whitout need to remove the ballast, soooo, no matter if gets the reduced voltage while in RUN, ALTHOUGH tipically everybody removes ballast and splice all wires together, sourcing on that way full 12 volts on both ign switch stages.

If you were to keep stock ign system, which requires the ballast, and the device you want to wire demands a full 12 volts for trigger it on ( so not like the MSD modules which accept reduced voltage ), yes, will need a relay and wiring job on the wiring around the ballast to be able to source both system ( full and reduced voltages on both stages )... however if you will run an MSD Module won't need to keep the ballast setup

However you can also modify the stock ballast removing resistor element and installing jumper wires on grooves so won't hack up the wiring what happens when removing ballast or use ugly jumper wires attached to front of  ballast ( in case you want to reverse the job to the stock system ) to "bypass" the ballast and get full 12 volts on any stage just like this.

( I didn't make it, but I suggested and this guy did it )

[TommyGun]

What I would do is tie the brown and blue wires together and then use that to trigger a relay to feed power to the efi.

[lukedukem]

What I would do is tie the brown and blue wires together and then use that to trigger a relay to feed power to the efi.

Bingo. And Typical 12V automotive relays have a "pull in" voltage around 8V-9V, I believe. So it should be good

Luke

[birdsandbees]

I'm sorry guys.. but if when cranking you are pulling the voltage down below what will trigger your EFI then your battery is not up to the job, or your starter is on it's way out or both! Another option would be a small "alarm system" type battery that's only job is to run the EFI and recharged via the alternator through an isolator so it doesn't get pulled down by the main cranking battery.

[TommyGun]

The efi stuff is real picky about voltages. Could be more going on but pretty normal to pull voltage down a bit when cranking. At this point with upgraded ignition and alternater there really is no reason not to tie ignition 1&2 together as I think it's the easiest solution. Actually it's kinda funny the op put this up as fitech had a post about this on Facebook today and they recommend using a relay to supply correct voltage to the white wire.

[Nacho-RT74]

If he is thinking on use MSD, despite any relay. Ign 1 and 2 can be spliced together, jump both sides of ballast or mod the balast as the one pictured... nothing less nothing more.

If was to keep the original ign system, a relay should be used, and there are couple of ways to use it.

Would need to confirm if the relays catch the trigger signal on reduced voltage though, to make this job on one or another way ( is being discused at Moparts at this moment )

[68CoronetRT]

Maybe I should have been a little more thorough with my answer. Sorry to have you guys type out all these answers. I was really just trying to ask about a relay off the ignition for switched power.

Battery is brand new Yellow Top Optima.
Starter is a gear reduction mini starter
Brown and blue wires are tied together, ballast resistor is bypassed.
100amp GM 1 wire has been installed and amp meter bypassed.

Yes, Fitech posted that yesterday after I yelled at the owner over the phone 2 or 3 days ago because their tech support is a flat out joke. Luckily Summit is taking the fitech back and Holley kit is replacing it now. Unfortunately the Holley system needs to see a minimum of 11v at hard crank. The fitech only needs 10v.

I would have stayed with Fitech but after my system passed all their tests and proved their computer was dead, they denied it and would not help me out.

The voltage drop in my system has to be either the lack of battery wire from the trunk to the starter, or lack of grounds. That or I'm trying to use switched power after the bulk head connector and it's loosing it there. I'm just going to add a relay to the battery post(Starter solenoid), trigger the relay from the brown/blue wire, run ground with the EFI and starter solenoid. Done!

[JR]

Have you tried temporarily hooking the 12v signal input wire directly to the battery, just to see if it will start and stay running?

[68CoronetRT]

Ok, just to confirm the relay wiring.

86= Switched power source (Brown/Blue wires tied together)
85= Ground
87 = Power ON to MSD, EFI ECU etc... when key is on/cranking.
30 = +12v battery power (fused).

[TommyGun]

Correct.