Installation of an MSD #8739 2 step box:
The reason for the 2 step install was simple: the car is extremely quiet which makes hearing the engine RPM on the starting line basically impossible, esp. when the car in the other lane is running open headers. As such, consistently controlling launch rpm is damned near impossible. In an attempt to be able to launch the car consistently--and at a somewhat low rpm in an effort to reduce parts breakage, I decided to install and MSD #8739 2 step box to go along with my 6AL box.
The car was already equipped with a basic MSD 6AL unit which was mounted on the inner fender next to the battery both for convenience's sake and to help keep it somewhat less visible.
With the battery removed to make some room to work, the 2 step box was mounted next to the 6AL and the main power feed wire was ran straight to the battery junction post on the core support. Under normal operation, the 2 step uses the 2nd "module" which is the high rpm limit. When the 2 step is activated, it bypasses module 2 and energizes module 1, which is the low side. I chose to wire the 2 step by running power direct to the box and using a switch on the shifter handle to complete the ground circuit to activate the 2 step.
With everything back in place, the ground wire to the 2 step was routed through the engine bay above the passenger side inner fender, along the firewall and down the passenger side floorboard.
To activate the 2 step for the time being, I chose the classic Hurst t-handle which has a momentary contact switch built in. The wiring was ran down along the shifter handle and through the shifter grommet and under the car. One side of the wiring was grounded to the transmission crossmember and the other was attached to the ground wire to the 2 step box.
Note: I may change the wiring depending on how well it works as-is: MSD does show an alternate wiring schematic which uses a common 5 pole relay along with a clutch pedal mounted activation switch for the 2 step. The momentary contact button on the shifter handle activates the system while the clutch switch is energized, but the shifter button does not need to be held down as it does now. Once the system is activated and the clutch switch is tripped it de-activates the 2 step and reverts back to the high side chip.
Video of the 2 step-click the pic:
Hoping to get back to the track very soon.
Will the 3rd time be a charm? [img]<<GRAEMLIN_URL>>/rolleyes.gif[/img]