Question about wiring coming through bulkhead firewall, including the resistance wire

Hi folks,

I’m in the process of replacing the wires that come through the bulkhead firewall into the engine bay, including removing the resistance wire (hiding it actually as per the help instructions).

I have a couple of questions but I will start with some info:

The following is the bulkhead firewall wiring based on Figure 12-108 in the Cadillac repair manual:

To starter:

18 G Yellow (goes from starter to coil directly)

12 G Dark Blue

10 G Red

To coil:

20 G White with orange and violet cross tracer

18 G Yellow (goes from starter to coil directly)

To thermostat:

18 G Dark Green

Here is what comes out of my bulkhead firewall:

12 G Dark Blue that goes to a connector. The connector also has the 18 G yellow coming in AND out of it. See photos below.

10 G Red

18 G Dark green

On my setup, the white resistance wire is connected to a 18 G Yellow wire via a clip that connects to the coil (see first photo). If I delete or disconnect the resistance wire, I assume I need to run a new 18 G yellow wire from the coil to the starter, correct?  

If yes, then I can delete the connector that splits the dark blue wire (first photo) and just run a new 12 G Dark Blue wire to the starter?

I also have a white wire in the bulkhead firewall harness that loops from one side of the loom to the other with a female connector on each end (see photo below). I don’t see this wire in the repair manual diagram, so I have no idea what it’s for. Any thoughts?

Thanks in advance for both your input and patience as I fumble my way though this.

Oh and here are a couple of progress photos for your entertainment!

Balanced crankshaft

My good friend Bruce checking tolerances.

Almost there...

New vacuum lines run, new brake hard lines, suspension work underway. Then everything else...

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Most aftermarket setups will require a full 12 volts.  Regardless you will need power to positive side of coil at cranking and run position with ignition switch.  Yellow wire from starter already provides 12 volts in Crank position.  To get full 12 volt in run position, simply replace resistor wire back to where it ties into pink ignition wire behind dash with a new regular 13 gauge wire. 

Thank you Jason! That makes total sense. Now to find where the resistor wire ties in to the pink ignition wire....but at least the dash cap is off so that shouldn't be too hard.

On some parts cars I have been able to remove the screws holding the cranking harness bracket from the firewall and pull all wires forward enough to reach the "pink ignition wire" but on some cars it seems like that is not possible. Might be worth a try. Regardless, here is a picture of the 64 cranking harness showing the relative position of the firewall and how the resistor wire ties into the pink ignition wire. Might be of some help as a reference. Note the resistor wire path is outlined in blue from coil connect to tie into the pink harness inside firewall. (click picture to zoom in)

Thank you Jason.

I tracked down the connection point behind the dash and will swap out the resistance wire for a 13 G as you recommended.

Thanks again for your help! It is very much appreciated.

Really like your new fresh engine build
Great item to have in a new extensive restoration

Do be sure to double check that the rocker arms are installed correctly before firing the engine up
An error it seems many of the engine rebuilders ( best ?? ) have a problem with leading to bad oil circulation ( bad trouble ) from the get go when breaking in a brand new engine ---which is horrible
Motor oil that is correct for --a flat tappet cam is a must also for a sucessful break in

Hope you get many miles of enjoyment from your project
A very special Classic Antique Cadillac --i would say


Thank you Tony,

We have the rocker arms installed correctly in terms of oiling. We double checked everything during the build.

What is the recommended oil to use?


I think we need to know if you WB running a point dist or the pertronics electronic ignition
You will need the resistor wire installed if using stock points in your dist
The pertronics needs a full 12v always to operate so no resistor wire with that unite


I am going to install an electronic ignition system, specifically an HEI conversion:

Nice job on this tread gentlemen
Looks like Chris is squared away with the wiring issues


most oils you purchase at your local auto store off the shelf are no longer good for engines with the older flat tappet cams 

they are lacking the— zinc and phosphate quantities in there formula to protect our older engine 

they will damage a flat tappet cam engine ( cam goes flat ) 

I can only give you a heads up to be sure the motor oil you chose will be the correct formula  combination to protect your older engine 

We need that new engine performing great for the LONG HAUL after a good break in run 


Sorry I do not have —a brand - that I can recommend as there are ever so many opinions on oil brands 

a big part of the problem is finding a ——10w-30 motor oil weight ( per the shop manual ) that meets the requirements of the flat tappet cams 

this is one of the more difficult thing that we have had  to deal with —to keep our cars in good running condition that has changed over the years and requires some serious attention to keep our engines sound today 




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