Ignition, HEI, 351w keeps running

[dnfitz70]

I recently swapped in 351w. I added HEI into mix. After much research, I tapped power to wire in ignition switch to bypass resistance. Motor starts, all seems great until I turn key to off. Motor still runs until i have to pop lead at coil on HEI. When I test power lead with key in off position: 0.00 v. Key in run position: 12.1v

I resurrected engine sitting dead for 15yrs so I get she wants to run, but what am I missing here? Appreciate your input.

 

[bmc69]

That's usually caused by the alternator in a "one wire" setup. You have include a diode in the voltage "reference" wire that excites the alternator. Where did you tap in tho 12V?..and what model alternator are you running?

 

[Broncobowsher]

Alternator backfeeding ignition circuit.

 

[DirtDonk]

Original wiring harness it sounds like, since you said you had a resistor wire.
You can also occasionally get some backfeed through the starter relay if you are still using the brown “I“ wire terminal.
The HEI doesn’t need it, but if it was left connected to the ignition circuit, that could do it.
Is your bypass wire running straight from the ignition switch to the distributor? Or is it running from the ignition switch to the old red with green wire?

 

[DirtDonk]

Also, ignition switches do fail. You might have had a momentary failure, but when you tried to measure with the meter, the switch had temporarily corrected itself.
Have you tried firing it up again and turning it off to see if the problem persists and is repeatable?

 

[dnfitz70]

Original wiring harness it sounds like, since you said you had a resistor wire.
You can also occasionally get some backfeed through the starter relay if you are still using the brown “I“ wire terminal.
The HEI doesn’t need it, but if it was left connected to the ignition circuit, that could do it.
Is your bypass wire running straight from the ignition switch to the distributor? Or is it running from the ignition switch to the old red with green wire?

Thanks for the feedback. It was suggested to clip the red/grn (or salmon) at the ignition and run new feed from hei to clipped wire ignition side. The brown wire is still on "i" post, I was told and thought read that the brown wire is the extension of red/green. Red/green seems to be resistor. Maybe I'm wrong. Hindsight should have posted for advice. I have 71, original harness, came with 170, then 302 now 351w. Don't know exact alternator model. 65amp, intending to upgrade to one wire 100÷ amp

 

[DirtDonk]

It was suggested to clip the red/grn (or salmon) at the ignition and run new feed from hei to clipped wire ignition side.

The salmon colored section under the dash is the resistor wire. Generally speaking (though not 100% universal) the red with green wire is normal wire.
How much of the pink/brown/salmon wire was left and did you splce to that?

The brown wire is still on "i" post, I was told and thought read that the brown wire is the extension of red/green.

Correct. At the back of the engine at the multi wire connector, the brown wire is molded into the red with green wire.

Red/green seems to be resistor.

Not quite. It’s only the visual end in the engine compartment, of the resistor wire under the dash.
Under the dash the salmon colored wire is the resistor wire. Usually routed separate from the rest of the harness and covered in heat resistance, leaving to keep its heat away from the rest of the wires.

Hindsight should have posted for advice. I have 71, original harness, came with 170, then 302 now 351w.

A 71 should have had wire harness branches coming out of three places in the firewall. A bundle through a grommet on the passenger side, bundle through a grommet on the driver side, and a bundle through a grommet near the throttle linkage.
Is this how yours is laid out? Or do you still have these two large rectangular wire bundle connectors behind the engine on the firewall?
That layout ended sometime between 70 and 71, so thought I would check.

Don't know exact alternator model. 65amp, intending to upgrade to one wire 100÷ amp

Do you still have a voltage regulator somewhere on the fender or firewall?
Since you’re not sure about the model, you might double check to make sure there’s a voltage regulator connected, or not. Or what case style the alternator is.
There are 65 amp swaps from GM models that some people put in their Fords. Some of those could be one wire already.
If in doubt, post a picture of yours.

 

[Broncobowsher]

If it is a stock ford alternator with the external voltage regulator, try unplugging the regulator and start the engine and see if it will turn off.
Warning! Never plug or unplug the regulator with the engine running. This will fry the regulator most of the time.

The regulator is a very likely candidate for keeping the running with the key off. It is one of the few things that can do it, has both switched and unswitched power connected to it. Checking is easy, just one plug generally in a fairly easy to access location. And very likely to depower itself once the engine stops, unlike a stock I wire on the solenoid.

 

[dnfitz70]

The salmon colored section under the dash is the resistor wire. Generally speaking (though not 100% universal) the red with green wire is normal wire.
How much of the pink/brown/salmon wire was left and did you splce to that?

Correct. At the back of the engine at the multi wire connector, the brown wire is molded into the red with green wire.

Not quite. It’s only the visual end in the engine compartment, of the resistor wire under the dash.
Under the dash the salmon colored wire is the resistor wire. Usually

---

routed separate from the rest of the harness and covered in heat resistance, leaving to keep its heat away from the rest of the wires.

A 71 should have had wire harness branches coming out of three places in the firewall. A bundle through a grommet on the passenger side, bundle through a grommet on the driver side, and a bundle through a grommet near the throttle linkage.
Is this how yours is laid out? Or do you still have these two large rectangular wire bundle connectors behind the engine on the firewall?
That layout ended sometime between 70 and 71, so thought I would check.

Do you still have a voltage regulator somewhere on the fender or firewall?
Since you’re not sure about the model, you might double check to make sure there’s a voltage regulator connected, or not. Or what case style the alternator is.
There are 65 amp swaps from GM models that some people put in their Fords. Some of those could be one wire already.
If in doubt, post a picture of yours.

I have the 3 grommets layout as you described. The one in center closest to linkage also has a blue female connector. I have read it could provide power to choke. I still have voltage regulator on fender. The wire I snipped I do believe is red/grn but faded and looks salmon brown. The wire itself seemed like resistance. The core wires were more like steel, not copper.

 

[dnfitz70]

The salmon colored section under the dash is the resistor wire. Generally speaking (though not 100% universal) the red with green wire is normal wire.
How much of the pink/brown/salmon wire was left and did you splce to that?

Correct. At the back of the engine at the multi wire connector, the brown wire is molded into the red with green wire.

Not quite. It’s only the visual end in the engine compartment, of the resistor wire under the dash.
Under the dash the salmon colored wire is the resistor wire. Usually

---

routed separate from the rest of the harness and covered in heat resistance, leaving to keep its heat away from the rest of the wires.

A 71 should have had wire harness branches coming out of three places in the firewall. A bundle through a grommet on the passenger side, bundle through a grommet on the driver side, and a bundle through a grommet near the throttle linkage.
Is this how yours is laid out? Or do you still have these two large rectangular wire bundle connectors behind the engine on the firewall?
That layout ended sometime between 70 and 71, so thought I would check.

Do you still have a voltage regulator somewhere on the fender or firewall?
Since you’re not sure about the model, you might double check to make sure there’s a voltage regulator connected, or not. Or what case style the alternator is.
There are 65 amp swaps from GM models that some people put in their Fords. Some of those could be one wire already.
If in doubt, post a picture of yours.

I have the 3 grommets layout as you described. The one in center closest to linkage also has a blue female connector. I have read it could provide power to choke. I still have voltage regulator on fender The wire I snipped I do believe is red/grn but faded and looks salmon brown. The wire itself seemed like resistance. The core wires were more like steel, not copper.

 

[dnfitz70]

If it is a stock ford alternator with the external voltage regulator, try unplugging the regulator and start the engine and see if it will turn off.
Warning! Never plug or unplug the regulator with the engine running. This will fry the regulator most of the time.

The regulator is a very likely candidate for keeping the running with the key off. It is one of the few things that can do it, has both switched and unswitched power connected to it. Checking is easy, just one plug generally in a fairly easy to access location. And very likely to depower itself once the engine stops, unlike a stock I wire on the solenoid.

Well, you are on to something. I pulled the plug on regulator and started and stopped with key. So, does that indicate regulator or a portion is bad?

 

[Broncobowsher]

98% sure the regulator is bad.