Master Switch Wiring

Background
There have been at least 4 variations of wiring for the master switch on the SRF.   In this article, I’ll review all 4 and present the pro’s and con’s of each.
Wiring Style #1
This is the original wiring for the first 33 cars that were at the Runoffs in 1993.
.Master Switch _1.gif (11696 bytes)
Pro’s Con’s
- No parts of the car are “hot” with the master switch off.
- Zero current drain when the master switch is off.
- Engine does not shut off when the master switch is opened.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.
Wiring Style #2
Same as wiring style #1, but with a shorting resistor added to kill the alternator output when the master switch is opened -- thereby stopping the engine.
Master Switch _2.gif (11935 bytes)
Pro’s Con’s
- No parts of the car are “hot” with the master switch off.
- Zero current drain when the master switch is off.
- Engine shut off when the master switch is opened depends on the integrity of the shorting resistor and its wiring.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.
Wiring Style #3
Some significant changes here.  This diagram appeared in  the 2/17/94 update from Roush to SCCA Enterprises.  In this wiring style, the power to the ignition switch is taken through the normally open auxiliary contacts of the master switch.  Opening the master switch (putting it in the “normal” position), disconnects the battery from the alternator and the starter and --via the auxiliary contacts --- the alternator is disconnected from the ignition switch.  The tape-wrapped EEC power wire remains connected to the battery at all times.  This is the way my car is wired.
Master Switch _3.gif (11561 bytes)
Pro’s Con’s
- Fault codes are retained after the master switch is opened.
- EEC “learned” information is saved when the master switch is opened.
- EEC is “hot” at all times the battery is connected.
- Clearing Fault codes requires disconnecting the battery.
- EEC draws some (very small) current at all times
Wiring Style #4
This is the current “Green Book” wiring scheme.
Master Switch_4.gif (11775 bytes)
Pro’s Con’s
- Zero current drain when the master switch is off. - Alternator is “hot” at all times the battery is connected.
- Fault codes are not retained after the master switch is opened.
- EEC “learned” information is lost when the master switch is opened.

Rev. 3/14/98

Feedback
I welcome your comments or ideas on this information.  Feel free to drop me a line via “Comments for the Bro’s”.  

Barry

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