Wiring questions on new MS3X install

Hoytster

I don't dare do that to my Knob
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Dec 30, 2002
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I have a couple questions concerning the wiring for a couple functions from the MS3X expansion board I am hoping I can get some help with. For a little background, I'm planning on using an MS3X 3.0 ECU on a 363 cu/in boosted engine running COP and sequential injection. This is my first time wiring an MS3X so I'm trying to make sure I'm doing this correctly.

Tacho output:
I have (2) tachs I want to drive right now, the factory tach and an autometer 5" monster tach. I plan on using the "tacho" output on PIN 26 to drive the autometer directory since I'm pretty sure this tach will accept a 12V square wave input. I believe the factory tach will require a high voltage tach signal so I will need to convert the 12v square wave for this to work. Question is, can I tap the high voltage circuit off the 12V square wave signal going to the autometer and drive both tachs at once? Or will I need to use another output from the MS3X?

Variable fan speed control:
I'm planning to use PIN 27 to output a PWM signal to drive a Hella H41773001 SSR for fan speed control. I am going to wire a standard relay that is activated by ignition on power to apply and remove 12vdc+ to pin 30 on the SSR. Since the Hella SSR is only rated for 20amp continuous, I'm considering running each individual fan on my dual fan setup off (1) SSR. Question is, can (1) PWM signal from MS3X successfully drive (2) SSR's concurrently or will I need to use two outputs? Also, is it advisable to provide a full speed fan override circuit to drive the fans in case of an issue with the PWM control from the ECU? I'm thinking I could wire in a simple switch that would sink terminal 86 to ground and provide an override, but I didn't know if this would hurt the MS3X to do this?

Variable fuel pump control:
I'm planning on using PIN 25 for future fuel pump PWM speed control based on a fuel pressure input (I'll probably use PIN 21 for this). Same as the fan, I plan on using a Hella H41773001 SSR for this and will be wiring a standard relay controlled by the fuel pump output from the ECU to apply and remove 12vdc+ to pin 30 on the SSR (once I go to variable fuel pump control that is). Any concerns with this plan and would a manual speed override circuit be recommended here as well?
 
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a91what

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Tach, you should be able to make both happen with one output.

Fans, the pwm signal can be shared. an override should not damage the pwm output

Fuel pump, you would need to have a serious fuel pump requirement... for this to be needed.
 
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Hoytster

I don't dare do that to my Knob
10 Year Member
Dec 30, 2002
951
628
144
38
Cornwall, PA
Tach, you should be able to make both happen with one output.

Fans, the pwm signal can be shared. an override should not damage the pwm output

Fuel pump, you would need to have a serious fuel pump requirement... for this to be needed.

Awesome, thanks for the reply.

I'm running an Aeromotive A1000 equivalent (older Carter by Aeromotive pump, same flow). I don't have any problems right now with the fuel heating, but I might have to move to an eliminator pump down the road and just wanted to make sure I have option if needed. Aeromotive recommends a controller for the A1000 and eliminator for EFI street applications, so just CMA.