Purpose of these ECU leads?
05-31-20, 02:26 AM
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Purpose of these ECU leads?
Wiring gurus out there...I've been going through the wiring in my '91 NA S5 M/T trying to understand how some systems work/clean things up. I've gone through the diagrams and have been able to find most answers, but below are some ECU leads whose functions I'm still not fully clear on. If anyone could help me confirm/fill in any of the below for me, I'd appreciate it!
ECU leads -> function
1Q (clutch switch) -> engine idle control? Also looks to interface with cruise control logic (I guess deactivate cruise?) from diagram.
1R (neutral switch) -> engine idle control?
1S (fog light switch) -> ?
1T (Back-up light and 5th switch) -> 5th switch activates split air solenoid in ACV. The pinout also labels back-up light here. How does back-up light play into this, if at all?
3L (headlight switch) -> ?
3O (blower switch) -> ?
3P (rear defroster switch) -> ?
In particular 1S, 3L, 3O, 3P have me confused. I was under the impression these functions on the FC aren't interfaced through the ECU like in modern cars with CANBUS. Are they perhaps to signal the engine to idle up to increase alternator output?
ECU leads -> function
1Q (clutch switch) -> engine idle control? Also looks to interface with cruise control logic (I guess deactivate cruise?) from diagram.
1R (neutral switch) -> engine idle control?
1S (fog light switch) -> ?
1T (Back-up light and 5th switch) -> 5th switch activates split air solenoid in ACV. The pinout also labels back-up light here. How does back-up light play into this, if at all?
3L (headlight switch) -> ?
3O (blower switch) -> ?
3P (rear defroster switch) -> ?
In particular 1S, 3L, 3O, 3P have me confused. I was under the impression these functions on the FC aren't interfaced through the ECU like in modern cars with CANBUS. Are they perhaps to signal the engine to idle up to increase alternator output?
Last edited by Chef Jih; 05-31-20 at 02:44 AM. Reason: clarification
05-31-20, 08:48 AM
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the 1Q and 1R pins help the ECU determine idle. rpm needs to be under ~1100rpm, zero throttle and either the transmission in neutral or in gear with the clutch pushed in.
the others are so the ecu knows there are additional electrical loads on the engine, it changes the idle, some might do speed some do timing, i think there is a chart, but that might be from the S4's
the others are so the ecu knows there are additional electrical loads on the engine, it changes the idle, some might do speed some do timing, i think there is a chart, but that might be from the S4's
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