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Let's start this section by saying that I know a lot more about automotive wiring than I did 12 months ago.  This is one area that I wish I could just start and keep going until finished.   Using loads of forum suggestions, some wonderful assistance from Garage Freak and.... a few of my own ideas, I managed to design a schematic.   It started with a Painless Harness but basically scrapped everything but the fuse box..... used relays wherever possible, went with better wire, solder spliced, covered all joints with double wall heat shrink tubing, integrated a 37-pin AMP master dash disconnect,  mounted everything (drilled and tapped) possible on a hinged lower dash cover, and will cover all wiring using a high quality nylon loom I got from Waytek Wire.   The schematic is pretty cool.  Although this took an enormous amount of my time, I like to look at this as one of those things that sets my car apart ...... hmmm.... I wonder if you get one of these if you buy a Shelby or Superformance?  

As of 1/12/07 everything is connected .... every wire had a mate - I am still a little surprised at that.     I have tested everything (in as many combinations as I could imagine) with the exception the starting system.   Once I receive my CSR t-filler (hopefully this weekend).... this car will finally come to life.  

Cooling Setup:  I used a fused relay to power the fan (highly recommended) and added a toggle switch in case I wanted the fan to come one before the thermostat decided.  While adding a quick disconnect is not as necessary as say the headlights .... I decided to keep with the theme and add Weatherpacks for any external device.   In general they allow a nice robust way to disconnect devices and they are built to withstand outdoor conditions.  

Fuel Circuit:  Even though I'm using a carburetor,  I installed a fuel shutoff safety switch.  It will stop fuel flow in case of a rollover by preventing power from reaching the fuel pump. 

I also added a manual switch to turn the fuel pump on/off.  Kind of a "cool" factor but also adds a small level of added anti-theft security.   

Note:  The fuel safety switch is a very simple device.  When it is upside down, a ball bearing pushes the switch open.   The switch can only only be reset (closed) when it is in the upright position and weight of the bearing is off the switch. 

D.U.I. Ignition:  For those of you that spent a little more than you should have on a custom DUI like mine (which includes a custom distributor curve to match my engine profile).... here is how I wired it.  
Ignition CircuitA few guys have asked about how to wire a start button.   I am sure there are many ways but this is how I did it. 

 - With this setup the key must be in the "Run" position before the start button is pressed.

 - The "Crank" position of the key is not used (or wired).   You can turn the key to "crank" but nothing will happen.

- The key must be tuned off to disable the ignition (stop the engine).  (The start button is a start button only .... not a start/stop button)          


Master DisconnectI am sure that there are a few ways to wire this circuit.... this is how I did it ....and includes the following:

- remote battery terminal lugs

- the alternator and battery will both be shut down simultaneously - required for some tracks

- a 100A circuit breaker is protecting the system from alternator spikes

- a 60A circuit breaker is protecting the fuse box  

Headlight CircuitThis circuit is a culmination of a bunch of great forum ideas:

- VW latching relay and Flash to Pass  relay are controlled by the momentary button on the end of VW turn stalk. 

a) With the lights off, the high beams can be flashed as quickly as you can push the momentary button.

b) When the painless headlight switch is used to turn on the low beams,  the high beams can again be activated by pushing the momentary button.   

 - Since pin 56 and 56B are tied together, the low beams remain on when the high beams are turned on.  (more light) 

- a separate high beam relay is used to take the load off the switch and reduce heating issues that other members have noted with the painless setup.   

- the rheostat on the painless switch is used to dim the dash lights

 - to keep the front park lights on when the headlights are, connect both the parking light wire and tail light wire together and attach to the tail light terminal of the Painless switch. 

It all fits: Not a lot of room left though.  If you are curious... I created a separate section titled Dash Wiring.    
[Product Image]Relays:  Spared no expense here...Horn, High Beams, Flash-to-pass, Dimmer, Starter (for button or key starts), Fan, Fuel Pump and two extra  (a total of 9).  Also used  relay "connector" boxes to make wiring much easier (and more professional).   [Product Image]Dash Disconnect:  This 37 PIN Puppy took days to put together and solder.  It is cool and serves a purpose but...
Circuit Manual Reset Breakers replace Mega Fuse:   First Step - get rid of Mega Fuse.   Instead I used a 100A manual reset breaker to protect the fuse box/harness from nasty things that may come from the battery and/or alternator.   Then I used a 60A manual reset breaker to protect the fuse box/harness from spikes generated in the main fuse box power supply.     

Diodes & Secondary Circuit Breakers:   I used Radio Shack 6 amp "rectifier" diodes #276-1661 to restrict current flow. These diodes also have a 400A surge rating.   Because they are sensitive to heat, I decided not to solder but instead use some bus bars as my connection method.  Turned out pretty clean.

I also needed a few extra circuit breakers so I added 2 (20amp) and 2 (30 amp).  Notice that I also used the circuit breaker mounts and protective covers.         

Russ Thompson Turn Signal:   To keep with the theme of an easily removable dash I used two leftover WeatherPak connectors (3 pin & 2 pin) to provide an easy disconnect between column mounted turn signal and harness.     I am using the button on the end of my turn signal as my flash-to-pass switch. 

Cooling:   I have included a switch to manually override the cooling thermostat ... just in case.   

Heated Seats:   Passenger and Driver have hi/low switches for their seat heaters. 

Cooling Vents:   Passenger and Driver have switches for the Cobra Earl cooling fans.  

[Product Image]Battery Disconnect:   I mounted mine behind the passenger seat.  I used nylon loom and red electrical boots to protect all high current connections. 
[Product Image]Education-Steve wanted to learn so here he is cutting wires and soldering WeatherPak connectors for the tail-lights.   He did a great job!     


[Product Image]

Courtesy Lights:

Added switched lights for engine compartment,  trunk (click image) and one for driver and passenger foot box area (total=4).     This little baby caused me a bit of electrical grief.  One of the wires passing through firewall somehow got chafed, touched the firewall and when the circuit was energized, the fuse would blow. 

[Product Image]Speedo Sensor: This is what an electronic 8 pulse speedo sensor looks like (from Classic Instruments) 

[Product Image]Headlight Wiring :  Loads of great information on the Daniel Stern Lighting website.   I chose to run 10GA wiring from the relays to the headlights (including ground).    Overkill ...absolutely ... but I since I plan to run 7" Cibie's the extra capacity can't hurt.    Note use of shrink tubing to finish the job properly.  You'll need MetriPack for this application.        

[Product Image]Soldering 101: Solder splicing... Step #1:  fan wires  

Step #2: (click on picture)  carefully fit wires together and then twist.   

[Product Image]

Soldering 101: Solder splicing... Step #3:  heat wire from bottom .... let "wire- heat" melt the solder.    

Step #4: (click on picture)  note solder has encased wires.   

[Product Image]Soldering 101: Solder splicing... Final Step:   add heat shrink tube  


[Product Image]

Heat Shrink:

Hard to see with my poor photography but I went a little crazy with the heat shrink.  To make everything look nice and uniform, I even covered the connector shell with just a little hanging over the lip.   

[Product Image]Wire Loom:  Ditched the typical plastic loom and replaced with professional grade... split nylon loom.  Used about 100 ft of 1/2" and 50' of 3/4".   This stuff is awesome - but expensive. 

[Product Image]

Wire Loom:

All the wire harnesses coming together and entering dash area (from passenger side).

N.B. Pardon the dust on the polished panels 


1) Soldering: 
bulletI personally like a soldering gun ....a half pull on trigger will heat it up fast (you will feel and hear the humm) - a full pull will maintain the heat (no humm). 
bulletKeep a wet sponge, some soldering flux and good quality 60/40  (0.063") diameter rosen-core soldering wire handy.
bullet"tin" your soldering tip by heating, dipping in flux, and touching with solder - this will help with heat transfer.    If your tip gets dirty ....clean with a wire brush and repeat above.
bulletheat from one side of the wire and add solder to the other side (you want the "wire-heat" to melt the solder).  You get a bad "cold" joint if you don't follow this rule. 
bulletMinimize the amount of solder you use... too much and it will get drawn back along the wire (under the sheath) and create a hard sport that could break (and be difficult to detect).   
bulletAn excellent soldering source is  www.fordfuelinjection.com.
bulletIf you every have the need to solder-splice 3 x 10ga wires together you may have to resort to using two soldering guns to get enough heat to suck the solder into the wires..... ask me how I know!! 

2) Heat Shrink:  I started with a box of 4" assorted diameters of heat shrink tubing from  www.waytekwire.com.  What I didn't realize is that there is a big difference between  "single wall non-adhesive" heat shrink and double wall adhesive heat shrink.   The double wall stuff is far superior.    I went out and bought a Milwaukee variable heat gun for the job - what a great tool.

 3) Delphi WeatherPak and MetriPack connectors:  Don't skip this step - these connectors will protect all your exposed car wiring and provide a nice simple way to disconnect components like headlights, horn, etc.  Again you can buy from Waytek.

3) Circuit Testing:  Rather than risk flying something when testing your harness..... buy a 12V Lantern battery.  They are low amperage but enough to test most devices.... even will make your horn chirp quietly.   

4) Battery:  Warning.... if you own a Optima Spiral Cell battery ....and you have to charge for some reason (perhaps you left it on a shelf for too long) never, never use a charger that supplies more than 12V-1amp supply.  If you go higher you will fry the battery. 

5) Dielectric Grease:  A little goes a long way.  I have used it everywhere there is an electrical connection that might corrode.  All the Connectors, ground posts, plug wires, etc. 

6) License Plate Light:   While testing my headlights I would blow a fuse when the headlights were on.  After an hour of troubleshooting I traced the problem back to my wiring of the license plate light.   Turns out that the two studs on the back of the housing are not intended for a hot and ground wire.  They are for mounting only.   The hot and ground must be connected inside the light.    Should have looked at this light a little more carefully before wiring.     

I can be reached directly at the Legacy Garage at:  klegacy@comcast.net (SR71 on FFCobra.com)
Last modified: Sept 1, 2009