Installation of an original ballast resistor style "Rally-Pac" on my 65

Woody3882

Member
Jun 19, 2018
56
7
18
70
Bradenton Fl 34212
65 Mustang coupe 289. I need some help with a simple task that has turned into a cluster.
I am trying to install a Mustang “Rally Pac” tachometer and clock on my 65. No problem with the clock.
The tachometer instalation sheet states that there must be Ballast Resistor or a Resistor wire for the Tach to work properly. The 65 only produced the resistance wire from the ignition to the coil. But in order to accommodate the pointless ignition with full 12 volts, the resistance wire has been removed and replaced with regular wire. This practice was commonly done years ago to get full voltage and better performance with the pointless distributor.
My question is this, How do I get the tachometer to work without a resistance wire or can I modify somehow to make it work.

Question #2 The tachometer has three wires, one for the light bulb (black with blue tracer) no problem, The other two wires are the issue, they are one red and one black. I have read instructions and viewed various videos that give conflicting instructions. One wire goes to the ignition source and the other goes to the coil. Does anyone know which wire goes to where.
I appreciate any input that anyone can provide.
Thanks Woody
 
  • Sponsors(?)


StangNet created a new car social app called knowmoto! Add your Mustang or post a photo in the knowmoto app and enter for a chance at a $100 gift card from LMR. Click the LMR Logo for more about the knowmoto Mega Thread!

wicked93gs

10 Year Member
Sep 30, 2006
1,100
167
93
Nashville TN
Well....all a resistor wire is is a wire with a resistor in it...so really, all you need to know is what size resistor to use. You can fingure this out if you know what the voltage the rally pack is "supposed" to see...for example, the resistor wire running to the coil drops the voltage from 12v to 9v(give or take)...so if the rally pack needs to see 9v...just wire in one of those resistor wires and done...if needs to see some other voltage, then you need a different size resistor...you can figure out what resistor size you need with a formula once you know your desired voltage.

From a general tachometer perspective...there are 2 types of tach inputs:
1. Logic level...this is the type of signal received from an ECU...also known as a "clean" tach signal.
2. The other type is what vintage cars use...its a signal taken directly from a coil negative terminal.

Aftermarket tachs can use either type of signal....that rally pack(assuming its OEM or OEM-style reproduction) can only use the coil negative as a signal...so the black wire "should" be coil signal, the red wire should be hot-in-run-or-start, though I couldn't tell you where it needs to tie in to be correct.
 

Woody3882

Member
Jun 19, 2018
56
7
18
70
Bradenton Fl 34212
Well....all a resistor wire is is a wire with a resistor in it...so really, all you need to know is what size resistor to use. You can fingure this out if you know what the voltage the rally pack is "supposed" to see...for example, the resistor wire running to the coil drops the voltage from 12v to 9v(give or take)...so if the rally pack needs to see 9v...just wire in one of those resistor wires and done...if needs to see some other voltage, then you need a different size resistor...you can figure out what resistor size you need with a formula once you know your desired voltage.

From a general tachometer perspective...there are 2 types of tach inputs:
1. Logic level...this is the type of signal received from an ECU...also known as a "clean" tach signal.
2. The other type is what vintage cars use...its a signal taken directly from a coil negative terminal.

Aftermarket tachs can use either type of signal....that rally pack(assuming its OEM or OEM-style reproduction) can only use the coil negative as a signal...so the black wire "should" be coil signal, the red wire should be hot-in-run-or-start, though I couldn't tell you where it needs to tie in to be correct.
First I want to Thank you very much for your knowledgeable input. I appreciate it.
I bought a NOS resistor wire. but the problem is that the new upgraded electronic points need the full 12 volts, that is why it is common (old school method) to remove the resistor wire and replace it with a regular 14-16 Gauge ignition wire to the coil for optimum 12 volt performance. I feel that I can have either the regular 12 volt wire in for better performance but no (9volt) Tach, or a resistor wire in for 9 volts and the tach to work but lousy distributor performance. I was hoping that there was a way to keep the full 12 volts to the coil but also wire in the 9 volt resistor to make the 9 volt tach function.

A tip for others that find themselves with the same situation is that the 65 Mustang Rally-Pac sold by C J Pony/Scott Drake is a nice re-pop that is set up for the 12 volts, thus no problem. The other common online seller has the original (original being the key word) Rally Pac which requires a resistor in line to the coil or a resistor wire.
So if your 65 Mustang is restored as stock (9 volts to the coil) you need the Original Rally Pac, if you upgraded your Ignition system to have electronic 12 volt
Points then you need the C J Pony /Scott Drake Rally Pack
If I can not find a way to figure this out then I will have to spend another $300 to get the C J Pony/Scott Drake Rally Pac. Any advise is greatly appreciated .
Thanks [email protected]
 

wicked93gs

10 Year Member
Sep 30, 2006
1,100
167
93
Nashville TN
First I want to Thank you very much for your knowledgeable input. I appreciate it.
I bought a NOS resistor wire. but the problem is that the new upgraded electronic points need the full 12 volts, that is why it is common (old school method) to remove the resistor wire and replace it with a regular 14-16 Gauge ignition wire to the coil for optimum 12 volt performance. I feel that I can have either the regular 12 volt wire in for better performance but no (9volt) Tach, or a resistor wire in for 9 volts and the tach to work but lousy distributor performance. I was hoping that there was a way to keep the full 12 volts to the coil but also wire in the 9 volt resistor to make the 9 volt tach function.

A tip for others that find themselves with the same situation is that the 65 Mustang Rally-Pac sold by C J Pony/Scott Drake is a nice re-pop that is set up for the 12 volts, thus no problem. The other common online seller has the original (original being the key word) Rally Pac which requires a resistor in line to the coil or a resistor wire.
So if your 65 Mustang is restored as stock (9 volts to the coil) you need the Original Rally Pac, if you upgraded your Ignition system to have electronic 12 volt
Points then you need the C J Pony /Scott Drake Rally Pack
If I can not find a way to figure this out then I will have to spend another $300 to get the C J Pony/Scott Drake Rally Pac. Any advise is greatly appreciated .
Thanks [email protected]

What I mean is that you should install a resistor wire between the red wire on the tach and your 12v+ source. This will provide you 9v at the tach without affecting voltage to the coil. Resistors are not direction...they will resist in either direction...but since your tach is only pulling voltage and not providing any voltage on its own, the only thing that sees 9v this way is your tach.