Car: 1976 Charger Daytona, 360ci.

Issue: I have an electric in-tank fuel pump instead of the engine-driven pump assembly...prep for an eventual engine swap to a Magnum 360 on Holley Terminator X. When running, this pump is more than enough for a stock 360 (350 LPH). The problem is just that...when it is running. I'm finding that this pump cuts in and out at random times. It has been very difficult to diagnose. The pump has a power wire from Battery Positive and is grounded at both the front passenger fender ground and at one of the two fuel fill tube bolts inside of the trunk. I'm suspecting key-on 12v power is my issue. Right now, that is sourced from the electric choke connector (CE 14 per the book) because that was the only actual point of key-on 12v power I could locate. When the car is colder and as long as it doesn't drive too far or too hard, it's fine. But drive it hard, or try to take a roadtrip and eventually the car will choke out like the alternator died and the battery went flat. Let it sit a few minutes, it'll start up and move.

In preparation of the new engine, trans and ECU, I'm looking to see if there's a better key-on 12V source under the hood I can use instead of the choke's power supply. I was looking at the starter relay for a minute, but I only see 12v hot at the top terminal, 12V to solenoid for cranking and 12v ignition. I do not want to put a hard-mounted switch into this car. Am I missing any other key-on 12v sources?

The above is confusing as you are identifying two different 12v sources
Are you using a relay with the electric choke as a signal wire to "activate" the relay? If i am not mistaken the choke power is run through a timer or sensor to control it's temperature. might be wrong on that but I remember something to that effect with the choke on the mid to late 70's cars. If that's the case you may be on the wrong side of the controller. Regardless, A better source may be the IGN power TO the ballast resistor with a relay and fused battery lead

Wire it up and fuse and protect dedicated circuits. The under hood circuit you chose will draw very little to activate it,

I think you using the chock power is timed. It may not be constant, nor 12V.

Maybe tie into the bulkhead connector for the ignition? I'm a wiring ignoramous so I'm just guessing as what I'd do. Maybe ballast resistor feed wire? That should be 12V too?

He can use the 12 volt choke feed to activate a properly wired relay.

Agreed, which is why I stated

Quote

If that's the case you may be on the wrong side of the controller

but good to reiterate incase he missed that part

To many possibilities. It is either it is or it is not. Could be a tank full of crap choking off the pumps suction. Who knows.

That can be ruled out. The tank was dropped, emptied, flushed and prepared when the electric fuel pump went in.

Fair enough. Let's see if I can make it clearer:

*12v hot from battery positive to relay
*12v key-on signal from the choke's power-feed wire to relay
*Relay ground to passenger fender ground point
*Relay's 12v hot wire to pump positive
*Pump ground to trunk interior, grounded at bolt that holds fuel tank fill pump tube

You Should have a pod in the tank to prevent cavitation. Keeping it over 1/2 should eliminate that possibility. Where exactly are you hooked on at the choke? You could make up a simple light at the tank and run it somewhere visible in the car to monitor power. When it acts up if the light goes out its a power supply. If it stays on its the pump.

The tank has been topped off during testing. The fuel gauge is about as accurate as a blind, drunk man throwing a dart. On a stock 2-bbl 360, there's a blue wire that feeds power to what I can best describe as a circuit board that transfers power to the choke's element. I'm tapped into that power supply coming from the main engine harness, before the power gets to the choke's "circuit board". I'll add a picture later this evening if needed.

great idea Anybody wanna take bets ???

there is a field load relay under rt fender for alternator, it has a key on 12v source

Back when I put Holley Projection on Warhammer I did what you are doing, hung an electric pump on the end of the pickup.

Now the factory did that to feed a carb and deal with vapor lock issues, but with fuel injection it doesn't work well. As someone mentioned, at half a tank it'd suck air as the fuel sloshed away and it'd kill the engine when I made a spirited turn. The lower the fuel level got the more it appeared. Now I know you said the tank is full and probably isn't the issue, but I went thru a couple of burned out pumps dealing with this. If you get it on the road you might want to put in a hydramat on the end of the pump, at least. I ended up going with a fuel sump fed by the mechanical pump, that in turn fed the electric pump. Something to keep in mind is all.

As for you original question, use the ballast feed (12v side) to trigger your pump relay. Since if that is flaky your ignition would turn off too and it doesn't sound like your having an ignition issue.

There is a Hydramat on the end of that pump assembly. Wasn't going to pass up the opportunity to score one of those. This engine hasn't made a "spirited" run yet in my hands...nothing wilder than a 70mph Interstate cruise. Turns out I'm chasing a voltage regulation issue. I've seen the battery terminal reading as high as 17.1 volts at idle with lights on. New alternator is in, picking up new voltage regulator today.

voltage too high can be as bad as voltage too low. Some items get flaky in operation when the voltages exceed it's expectations.

Once you get you voltage problem corrected you should recheck you fuel pressure settings