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Discussion Starter #1
I can't find a switched power source on the car that is hot during start and run mode...

I have to finish wiring in this fuel injection system
And this is upsetting
 

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Not sure of the year, so a generic response to suggest running the line through the Radio circuit.
 

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Discussion Starter #3
I'm sorry
It's a 66 model
I think I have only two possible solutions

Ignition switch. I know the stud won't work
But what about the other wires on it

Two. The alternator
I have a source on it. But it remains power after I shut the car off until I disconnect the battery
Then it is dead until I restart the car
 

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I have a 69 which is a little different is areas from a 66, but one thing is for sure: they all use the same basic ignition circuit. When the key is in "run or start" they have power to the ignition coil. Power goes from battery+ to the ignition switch from B to C (on a 69) and is on in run and start. This goes through the factory tach if you have one and to the pink resistor wire, then on the the coil. If you don't have a tach it just goes from the ignition switch to the resistor wire. You need to make a connection between the ignition switch and the resistor wire. Since I have no need for a 66 wire diagram I can't tell you the wire colors, but someone on here will know. Good luck.
 

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I comes out of the ignition switch with a black/green or red/green wire, then into the pink resistor wire. I just did the same thing wiring up FiTech. I had to bypass the pink resistor wire when I installed a new coil a while back to get 12 volts with key on and cranking.

 

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The pink resistor wire limits current and not voltage. If all you need is a signal wire to turn on an ECU or MSD, the current is so low it will not drop voltage. There is a + wire to the battery that carries the load to run the ECU and/or the MSD.
It depends on the application. My FiTech and Petronix CDI has a wire that goes to the battery and requires a 12v switched power source for key on and crank. If you splice in after the pink wire, you won't get 12v.

If the pink resistor wire doesn't limit voltage, why do stock coils measure 6v to 9v at the coil?

Tim
 

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It depends on the application. My FiTech and Petronix CDI has a wire that goes to the battery and requires a 12v switched power source for key on and crank. If you splice in after the pink wire, you won't get 12v.

If the pink resistor wire doesn't limit voltage, why do stock coils measure 6v to 9v at the coil?

Tim
The "pink" wire is a resistor. Resistors control current. That's their electronic/electrical
purpose. They let you determine how much current flows for a given voltage. Easy concept
if you consider regular wires as having no or extremely low resistance by themselves.

Quick summary- A resistor limits the flow of electrons, reducing current. Voltage comes
into play though because of the potential energy difference across the resistor.
 

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Quick summary- A resistor limits the flow of electrons, reducing current. Voltage comes
into play though because of the potential energy difference across the resistor.
I'm no electrician, but I understand what you are saying. My point was that regardless of how you look at it, you will not get 12v if splice in after the pink resistor wire.

Tim
 

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Toss a Bosch-style relay near your FI unit, grab the power supply from the battery (typically at the front lug on the starter solenoid) and the relay switch wire from a jumper to the "I" wire on the solenoid. The "I" wire is hot when cranking (12v) and "I" hot in run being back-fed from the coil+ feed.
 

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I'm no electrician, but I understand what you are saying. My point was that regardless of how you look at it, you will not get 12v if splice in after the pink resistor wire.
You got the basic jist right. There won't be 12 volts after the resistor. Current through a resistance causes a voltage drop. Ohm's Law. The resistor limits the current and by doing so causes the voltage on the load side (in this case the coil side) to drop accordingly. You'd use the value of the resistor to control how much voltage drop you get.

https://en.wikipedia.org/wiki/Voltage_drop#Voltage_drop_in_direct-current_circuits:_resistance
 

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I can't find a switched power source on the car that is hot during start and run mode...

I have to finish wiring in this fuel injection system
And this is upsetting
Did you check the ignition switch C (coil) terminal? That terminal has a RED/GRN wire on it and should be hot in ON (run) and START.

Paul
 

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Fortunately someone posted a 66 wire diagram and that makes this simple, so lets use that. Going from the 66 wire diagram above: run a 20 to 18ga wire to the 297 wire that comes from the ignition switch (#297 black with green stripe) or if easier you could splice in to the next wire, (#16 red with green stripe). Run your new wire to the coil of a 12v relay. Connect the other relay coil connection to chassis. Connect the relay common contact to battery+ and your EFI to the normally open relay contact.
The relay should have a 12v coil (two connections), a common and NO (or normally open) contact. That's all you need- 4 connections to the relay. For the common and NO wires use the same gauge wire as those coming from the EFI.
 

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There absolutely is not enough dedicated and switched power on the first gen mustangs. Take Mach1's advise a step further, put in a dedicated 8-circuit fuse panel with a 30A load and use a relay to trigger that panel off of switched power. You'll thank yourself later. Once in place you'll always have a dedicated, safely protected, switched power source, for gauges, tach, mini-USB, etc.
 
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