EFI- old MoPar- where to get "true power"? Start/run

We are converting a 1969 B body to EFI. Instructions say ECU needs a wire to go to start AND crank 12volt power. Power cannot drop below 9 volts. We tried the ballast, it's a 4 pin ballast, but nowhere do we get sustained 9+ volts during start AND run.

I thought relay maybe? Would 6 volt at ballast pull in a relay?

What has been done for a 1969 B body to get voltage for start and run power at the ECU that works??

There is no ONE source for that. In start the ignition switch feeds the coil 12v bypassing the ballast, in run the ignition switch shuts that feed off and feeds the coil through the ballast. You need to tie both of those feeds together to get the 12v power your EFI is looking for. Are you using the EFI for ignition as well? If so you can just tie those two feeds together. If you plan to use a separate ignition you will need to use a diode to isolate the feeds from each other while they still feed the EFI.

I'd use those feeds to run a relay and use the relay to feed the EFI direct from the battery.

On my '65 B body I tie start and run together and use the combined switched 12 volt to power the EFI and the ignition system. I also use it to power up the alternator although the alternator really only needs the run line. However, once you tie them together they are together unless you get fancy. My car has been "modernized" so I ditched all of the old Mopar wiring. No more ballast resistor, no more start and run circuits, no more passing all current thru the firewall to the ammeter, etc. Trashed all of that old school Mopar engineering.....

I did similar to Andy. If you're using modern ignition you don't want the ballast in there anymore reducing the voltage anyway. Tie it together and bypass the ampmeter circuit while you're in there

You can make a doube ended male jumper wire that slides into both of the existing female wire ends at the ballast resistor to do what you need
I do it all the time on street and race cars that I install MSD race boxes or any other ECU that doesn't want the stock Mopar ballast resitor
Simple and effective

K so...... we tried many things. The instructions are from the Professional Products kit. It says to go to the power side of the (4 pin) ballast resistor. It also says voltage should not drop below 9 volts at any time.

Voltage drops below 9 volts if wired as it says.

We tried to run side of ballast and it doesn't start as easily as if we run the wire directly to the battery.
We read the instructions again and it says to pull the power directly off the + side of the coil. But not if a ballast resistor is used. This actually works the best by far.

We then thought maybe a relay pulled in by the coil voltage with 12 volts coming directly from the battery might even work better. We are just concerned about pulling a coil in from the positive + coil terminal.

Ma Mopar... what were you thinking? lol
So.... he has an Ehrenberg box I believe the HiRev kit. Can we get rid of the 4 pin ballast somehow?
Argh.

Kit runs pretty danged good, hasn't had time to learn much but it's got throttle response and once running it's no complaint here. We don't want to fry coils and relays and wires by doing things wrong.
"True Power"? Engine maybe! We have ignition 1 and Ignition 2!
We are trying to wrap our heads around the response so far! Thanks. Thanks for being patient!

you might have wired it to the wrong side of the ballast.

check the other pin, see if it stays above 12 volts.

I noticed more than once that the wiring is reversed on the ballast, in that the side you think is going to the coil is not the one it looks like it should be.

since the ballast doesn't care which way the power goes through it, my bet is you are looking at the side coming out instead of going in if you are seeing a drop to 8 volts.

Here's our diagrams we used

We have the 4 pin ballast. We considered swapping to a 2 pin ballast. Whatever works! lol

The problem is that you are trying to keep the ballast resistor and stock ignition while also not keeping it. It is easier and cleaner to make up your mind and go one direction.

If you insist on keeping both start and run circuits for your old school ignition setup then you'll have to do something fancy to power your EFI.

Put two jumpers in instead of one
As Andy has pointed out you may be reading the wrong end of the resistors, bypass both of them

I went through this when I did my FiTech.
Simple solution to keep ballast is just add a diode across it.

https://board.moparts.org/ubbthreads/ubbt...tml#Post2387708

We have the ballast still in place and feed the fitech with it's wires. The switched/run 12v source just tells it when you want it to actually run. The b+ 12v source powers the unit as a whole.

AWESOME.

Diode hunting we go. Thanks everybody!!!!

As mentioned, either tie run and start together and use an ignition that does not use a ballast resistor, or put a Diode across the ballast resistor.

You need to know that all diodes are a one way electrical devise use to stop the current from reversing, flowing backwards, one way
I'm not sure if they are current limited or not Meaning maybe you can you blow them open with to much current They are used to rectify A.C. from alternating to direct current in alternators when used as a full wave circuit
IHThs
OP, does your EFI and ignition require a specific lower voltage to the ignition ECU? If not bypass the resitors

Yes, Diodes need to be sized for the current flowing through them.
I think the post linked ti mentions a 1N400x diode, but I think those are only rated for 1-Amp, and have a 0.7 volt drop across the diode.

I recall another thread where a 15 amp schottky diode was used.
I think looking up solar array blocking diodes. They also have less voltage drop, about 0.5 to 0.6 volts.
The diodes are pretty inexpensive too.

Correct, in the link above there's an EBay link for diodes used in solar panels.
Plenty of current capability and only $1 each.

Here it is again, I put 2 in parallel as a safeguard in case 1 of them fails.
Plus it doubles the current available.

https://www.ebay.com/itm/Pack-Of-10-Scho...a-/381734805254

Or you could just use that signal to trigger a 30A relay fed directly from the battery and avoid all the old wiring issues.

Still need to combine start and run, relays aren't small.

Did I miss something? Not sure why you need to keep the ballast at all. Just hook it up like you would an MSD by attaching the start and run wires and get rid of the ballast--that should give you the consistent voltage you need.

Yes, they are. Every new car out there used a bunch of relays to power high loads. they are not big, they are not expensive and they are not a mystery to be avoided.

Nor do you need to dance around in the nude and sacrifice a chicken to the god of electrons.

Any other objections?


This 30A automotive grade relay is 2" tall and about 1.24" square, Under $4 and includes a mounting tab.

the connector if you want one. Under $4 again.

EFI doesn’t suck lot of load. We have talked about that in several threads. Take the power from the Blue run circuit and install a Diode between ballast prongs to get 12 volts on both ign positions without affect the power to coil while in RUN

So you're saying I can replace the 1/4" diode with a 2"x4" relay? That's great news, thx for the insight.

My buddy opted to run power from the ballast to a relay, and has the ECU powered from the battery- interrupted by lack of ballast resisitor power. We might run the diode. Just getting a diode isn't easy on a Sunday!

It's a Professional Products EFI kit, says to run direct to coil but cannot drop below 9 volts. The instructions are more confusing than the actual work! lol
This is the same ECU that had me ask a couple months ago.... "Rear wheel torque for 440"!!! It wanted a value. We ended up using 400 ft lbs.
Geez

.....‘‘tis a good nite - da Bolts the ‘nucks !