bwirolla64

I need help with wiring my fans. Picture #1 is how the wiring is if I have a standard SBC. Picture #2 is how I think it should be wired now that I have a LS3/computer. Let me know what you guys thinn! thanks

FatfreeGTO

On mine I only have a single fan but its not done like that. Mine is done as follows.

The PCM is only completing the "ground" to the relay pin 85. Pin 86 gets 12v from the ignition being switched on. My fan doesn't run when I turn off the ignition but then again I really wouldn't want it to simply because of the drain on the battery. Pins 30, and 87 are the same as mine.

bwirolla64

On the paper from Speartech it says that the pink w/black wire is 12v key on to pin 85. the dark blue and dark green are ECM ground control to pin 86. That would be opposite from what you have described?

99VetteFRC

I am using a '03 truck PCM and it has no fan control cucuit. I am going to use a universal thermostat with a probe that goes into the radiator fins to control the fans. They have a small screw to adjust the temp.

bwirolla64

If I go that route should I remove the coolant temp sensor from the driver side head that has a plug or leave it plugged in?

99VetteFRC

You have to leave it plugged in. The PCM uses that signal for a/f ratios and open/closed loop operations.

bwirolla64

VERY good info to know!! Thanks 99

bczee

iTrader: (12)

On my Chevelle. I used a standalone system that is not linked or wired into the PCM. I used two SPAL fans and there standalone controller. I can set the two temp to come on for low and high speed on the fly. I was able to use the 99 temp sender on the driver side head to input into the SPAL PWM controller. Has worked well for over 5 years.

Just another option.

FatfreeGTO

You are correct mine is 85 12v, 86 ground. It was late and I guess I wasn't thinking straight.

bwirolla64

Lol lol I know how that goes! I will try it out and see if that works.

cutlass_455

iTrader: (2)

Check out this pic of how is used to be done in old days of the LS1/6.

Its for low speed and high speed control.

Andy1

I did my LS1 ('01) using that factory fan switching scheme, and it works great. I prefer the idea of the two low speed fans and two high speed speed fans as opposed to the one high speed fan or two high speed fan switching; the latter is a lot noisier.

I'm not familiar with the LS3 PCM switching, but by your scematic it looks the same as my LS1. The stock LS1 switching scheme runs two fans in series (so each fan sees 6V) for low speed, then switches to parallel (so each fan sees 12V) for high speed.

Andys