Doing a FiTech fuel injection install.
Need to find 12V that is hot during cranking and engine running.

Where's a good spot to tap in for this?

Thx

What ign system do you have? That could change lot of things


Need to ask... that source is just to trigger it ON, or will be THE POWER source?

The factory harness has separate ignition switch wires for crank and run. On my FI install I simply spliced these together in the engine compartment to trigger the computer. It is a big splice because the ignition box and fuel pump relay need the same signal.

the downstream (brown wire) end of the ballast would have ~10 ish volts during cranking (ign2) and that same terminal would have a reduced voltage (maybe ~8ish volts in ign1 (run) with the reduction thru the ballast. (if that would be enough to work for what you have in mind).

I'd seriously advise only using this splice to control a relay that supplies the 12V to the FiTech unit.

I have the Mopar electronic distributor with an Orange box.
The connection needed during crank and run is just a trigger.
The FiTech throttle body has a built in relay to feed the fuel pump.

On my setup main power to the FI computer comes from a heavy wire right from the fender relay. The ignition switch feed I described runs a relay inside the control box to switch it on... and carries very little current. Agree the ignition switched lines I used are not suitable for main power supply.

You can use an ISO relay to supply power to the FI Tech in both crank and run.

Ok, having stock setup system ( coil feeded from ballast )and the signal required is just a trigger to turn on the system the SAFER and easier way to get power on both stages is get that signal from blue circuit before the ballast, the same used for the ECU and regulator. No need for extra relays with this.

Even is true this circuit is feeded directly from ign switch just on RUN ( ign1 ) getting 12 volts, while cranking is also sourced from the opposite side of ballast coming from Ign 2 circuit, being the ballast the splice, getting together both circuits, although getting a dimmed power while cranking ( 4-9 volts ) on run circuit. That voltage rate should be enough to keep on the EFI system working whil cranking IF is true the source you need is just a trigger on signal.

If this wasn't posible, the ECU will never be sourced while cranking either, so engine would never start

AAAAND that's why the cluster brake light dims out while cranking, because this bulb is feeded from same run ( ign 1 ) circuit BUT ign 2 coming out from the oposite side of ballast.

John, I guess your idea is use the 30 lead of relay to feed the trigger to the EFI.

althought initially it seems a good idea, remember the ballast output to the coil is allways hot, no matter the ign switch stage ( as far ballast is conected on both sides ), so even with a reduced voltage, the relay could be still being triggered at 86 lead from the ballast, so 30 lead will be getting powered from IGN2 ( 87 lead ) allways which is Also the same 86 source. There is a bucle anyway like there is no relay

The EFI system ON signal load could be SO SMALL that the coil source could work too without affect the ballast voltage HOWEVER, better use the Ign1 side, in that way the Ballast will be affected just while cranking

That's where you're wrong, in Start the blue wire (IGN 1) shuts off and the brown wire (IGN 2) powers the ignition by bypassing the ballast, in Run the brown wire shuts off and the system is again powered by the blue wire.

At no time are both the IGN1 and IGN2 circuits powered at the same time.

From ign switch yes, is as you mentioned, but once both circuits are conected to the ballast, both circuits are hot, just at diff voltage rates ( selected from the ign switch ). The Ballast is a "virtual" splice.

When in ign1 12 volts is being sourced from ign switch, ign 2 gets 4-9 volts from same circuit throught the ballast in RUN position

When in ign 2 12 volst is being sourced from ign switch, ign 1 gets 4-9 volts from same circuit, throught the ballast in START position.

And that's how the ECU even is sourced from ign 1, it gets still power while cranking ( same as the cluster brake bulb )

And for the same reason, the coil gets the power in both positions ( so allways hot ) no matter the ign switch position, but just at diff voltage rates.

Think on it

The problem is, the FI Tech (the subject of this discussion) needs a constant 12V source, not the reduced voltage from the ballast. Some systems, like the MSD, will work on a lower trigger voltage.

OOOH, OK! That's a diff story

Ok, but still, The diagram you draw will keep working from 87 terminal no matter if run circuit is linked with 87a, because the 86 terminal will keep allways hot... UNLESS, the reduced voltage coming out from ballast to feed the coil is not able to keep activated the relay at 86... what I don't really know. Never have tried to keep those relays activated with the "low" voltage could come from the ballast.

A diode will definitelly help just between ballast and splice feeding 86 terminal on ign 2 circuit, to be sure the low voltage coming out from ballast on RUN won't activate the relay and the voltage coming out from 30 to trig on the EFI will keep working with 87a 12 volts coming from ign 1 ( run )

Like John said. Splice the dk blue and the brown together from the ignition switch. Neither is reduced voltage.
Doug

i think it goes like this...

connect ign 1 and 2 to terminal 86 as the turn on voltage
85 to ground
30 is your fused 12v source from the battery
87 is your relayed output, i would look for a double output relay (87b terminal) in case i needed two relayed 12v sources...

http://www.12voltplanet.co.uk/relay-guide.html

Sigh...

87A is the normally closed circuit, so IGN1 Run power flows through it to 30 as the 12V source. When power is supplied by IGN2 in Start, it powers 86 which activates the relay and sends power through 87 which is normally open and closes when the relay is activated. This way there is 12V at terminal 30 in both Start and Run.

Is just right like John detailed and is a GREAT useage for the relay, which usually we use it on the other way around. But my main concern is if the low voltage coming out from ballast ( the same that feeds the coil on RUN ) could still activate the 86 prong to keep closed the circuit allways to 87 side ( ign 2 circuit ) which will keep on low voltage rate while in RUN. That's why I think could be a great idea to get a diode to block the low voltage coming out from ballast up to ign 2 side, just right before the splice to feed the 86 prong.

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

oh right, i didn't see that he wanted to keep all of the factory ignition (ballast and all that). figured since he was doing EFI he was doing a different ignition too.

seems using a relay in the fashion you described would work well.