Wiring the Ignition Switch...

Okay Folks,

This is one of the most important video and posts in the entire ISIS video series showing you how to wire our panel truck.  In this video, I show you how to wire the ignition switch to the MASTERCELL.  We are going to repeat this process for every other switch in the truck.

We keeping the original switches that came with the truck.  They are in great shape and we like the retro look, for now.  In the not too distant future, we are going to replace all of the switches on the dash with our inTOUCH MAX Touch Screen and take the truck to a whole new level. 

As we have been working through the truck, we have found some scary electrical things.  The truck was originally built with a 6-volt electrical system.  In the early 1980's, it was rewired with a 12-volt system.  When it was rewired, they did two disturbing things.  First, there are no relays anywhere in the truck.  This means that the full loads of the accessories are flowing through the 50+ year old contacts on the switches.  Second, there are absolutely no fuses anywhere in the truck wiring system.  There was nothing to protect any of the wires from overheating if there were any shorts or any breaks to ground.  We fixed all of that with ISIS. 

The original switch layout in the truck has a keyed ignition switch and a separate push button to engage the starter solenoid.  We are wiring it exactly like this diagram in our reference library.  This link will take you to a downloadable version of this. 

In other posts, we have talked about how the MASTERCELL inputs work.  Instead of running the full load current through the switch, the switch triggers a ground signal to the MASTERCELL.  It takes less than 1 milliamp (0.001-amps) of current to turn on an input.  This is really important since we are using the original 1955 switches.  The contacts from those 56 year old switches will never burn up because of carrying excessive current. 

The MASTERCELL inputs simply need to be pulled to ground to turn on.  The input wire goes to one terminal on the switch and the other terminal connects to ground.  When the switch is on, you have a path to ground that triggers the input on the MASTERCELL.  You have two options for ground.  First, we give you several ground wires in the MASTERCELL input connectors.  Second, you can ground the switch right to the chassis as long as you can get a good connection. 

Here's where most guys have to flip their thinking over when it comes to wiring cars.  You are going to use the switch in the car to ground an input to the MASTERCELL, instead of applying power to the switch.  In most cases, you are going to use the terminal on the switch that connected to the battery as the connection to ground with ISIS. 

In the case of our ignition switch, there is a terminal labeled B+.  Originally, that connected to the battery and was the feed to the other terminals on the switch.  The IGN terminal connected to all of the ignition switched functions.  Current flowed from the B+ terminal to the IGN terminal when it was wired originally. 

With ISIS, we grounded the B+ terminal on the switch and connected the IGN terminal to the ignition wire in the MASTERCELL harness.  When the switch is on, current flows from the MASTERCELL input wire, through the switch, out the B+ terminal to ground.  Again, this is very little current flowing so the wires can be just 22 AWG.  Compared to what was on that switch originally, there is much less bulk of harness behind the dash. 

Check out our latest video for more commentary on this. 


You can catch the rest of our video series at our website by clicking here. 

Keep watching for more videos from our F100 Install Series.