MS3X IAC1A as boost control
 

I hate asking about this, but I can't locate the reference I used when wiring this up.

I read somewhere that you can use 1/2 of the stepper motor controls (IAC1A or IAC2A) on a MS3X to control a slow frequency solenoid valve (such as a MAC 4 port.) 6 months after completing my wiring harness (and after putting some miles on the car), I get around to hooking up the boost valve. I wire one side of the valve to 12V and the other to IAC1A. Now the oil cooler fan turns on as soon as I reconnect the battery, without the power to the ECU turned on. Power up the ECU, and the main engine fan turns on. Did not leave it on long enough to do any testing. I cut the wires on the valve and everything returned to normal. The car still runs (yea!).

Wired like this:

MS3X:
24 Nitrous 1: Oil Pressure warning light
6 Boost: Main Relay (late model NB2 ECU controls this, and my wiring harness is out of a 2005)
25 Nitrous 2: Main Fan
26 Tacho: Tach
27 VVT: VVT
9 Idle: Idle
21 Spare ADC: Oil Temp
22 EGO 2: Oil Press
23 EXT_MAP: Rotrex oil temp

MS3:
25 IAC1A: Boost Valve
29 IAC2A: Rotrex oil cooler fan
30 Fidle: Oil Cooler Fan

Thanks for the help,

John

Do you have the flyback diodes installed for the fan?

also, do you have your main relay (or was it the fuel inj relay?) unplugged in the fuse box? Because if it is, the main fan will come on telling you it's broken or unplugged. Had this happen to me before where I forgot to plug it back in when powering up the megasquirt and the fans kept coming on making me think I had messed up my wiring