FULL ON/OFF 12V

[brunoffrance]

Hi the community,

I try to install an electronic ignition PERTRONIX on my 73 and I have to connect the coil ignition to a full ON /OFF 12 v ....
Where can I find and plug to get a FULL ON/OFF 12 v ?
Is the alternator a good choice to share his 12v ?

Thank you for your advices .

bruno.

[Lee]

Bruno, there may be 12v sources under the hood that are live with the key in the ON position (you’ll need to check with a meter), but if you go that route, make sure it is also live in the START position. There are some disadvantages to this method, namely, possible voltage drop across a circuit that was never designed for the added current draw. No matter what you decide to do, I would avoid the temptation to use one of the cheap tap-splices. They never last very long in my experience:

Assuming you have the Pertronix 2 or 3, I would suggest that you do it the way I did: get one of the very cheap and common Bosch automotive relays (normally open), and trigger it with the existing resistor wire to the coil. The 12v source can then be pulled from the battery side of the starter solenoid, and you’ll be assured of a strong 12V source at all times.

So, in the diagram below, pin 85 will be the current + wire to the coil (the relay coil is very high resistance, so the resistor wire doesn’t matter, it will still have sufficient voltage to operate the relay), and pin 86 will go to a good ground on the body or engine. Pin 30 goes to the battery side of the starter solenoid, and 87 goes to the coil + terminal. This method has been very reliable for me.

[brunoffrance]

hi Lee,

Always in first position to reply and thank you one more time ....

Pin 85 ; is it the red wire (+ ) from the distributor PETRONIX III to the coil or the stock wire (+) ON/OFF from key contact ?

You advice me the pin 30 to the battery side of the starter solenoid ... which pin ? the pin from battery (+) or the other (- )?

may be a schema with the relay and the PERTRONIX ( 2 wires ) to be sure of the wiring ....

Thank you by advance?

bruno.

[Lee]

hi Lee,

Always in first position to reply and thank you one more time ....

Pin 85 ; is it the red wire (+ ) from the distributor PETRONIX III to the coil or the stock wire (+) ON/OFF from key contact ?

You advice me the pin 30 to the battery side of the starter solenoid ... which pin ? the pin from battery (+) or the other (- )?

may be a schema with the relay and the PERTRONIX ( 2 wires ) to be sure of the wiring ....

Thank you by advance?

bruno.

Pin 85 attaches to the stock wire that goes to the coil (the resistor wire).

Then 87 goes to the coil:

For pin 30, you will need to run a new wire and large ring terminal to the battery side of the solenoid (whichever big terminal goes to the battery, some solenoids are mounted upside down). I would use 16 gauge or larger.

[brunoffrance]

Great, I'll going to do what you say with the relay .... I've to find the famous starter solenoid and the good plug in red on your picture ( 2 possibilities ? ) ....

[1Bad55Chevy]

I am pretty sure the Mark IV does not use a remote solenoid. From my understanding the 70 Mark iii was the last to use to remote solenoid. The solenoid should be mounted on the starter.

[Lee]

Thanks Chevy. I didn’t know that.

Bruno, if that is true, then just attach your main 12V terminal (pin 30) to wherever the positive battery cable stops. You are just looking for a good strong source of constant 12+ volts

[brunoffrance]

OK for that .... Thank you for the advices !

bruno.

[brunoffrance]

Hi lee & chevy,
finally I 've taken the positive and negative, directly from the battery .... the circuit with relay is made and the engine didn't want to start . After a lot of time to find the good adjutement , turning by hand the motor, it starts and it was possible to get a 14 degree advance @ 650 rpm with a strobe light lamp ... but what a work ! When PETRONIX said " plus & play " ... it's a joke !

Thank you one more time for yours advices !

[Lee]

Glad to hear it Bruno! I think you will be very pleased with the performance.

[Bamboobert]

After I read this post, I built in the Petronix this way in my 72 MK4. Works great! I took the 12V direct from the battery, should there be a fuse build in somewhere?