i have installed an electric fan assembly in my 69 charger from a late model challenger/charger with a hemi.
it will cool an aluminum cross flow radiator [not installed yet.
this picture doesn't show it, but the assembly has been form fitted to the core support, and the radiator will be mounted ahead of the support [yes, it will fit with a couple of slight mods to the core support and the hood latch support].

my question. which fan is the main cooling fan ? the driver's side [upper fan] or the passenger side ?
or does it matter ?
powerplant will be a modded RB.
i am also adding AC.
as is always the case, TIA !

It really does not matter, you really need a Pulse width Modulator for those fans.

is that the dodad that spins the fan[s] faster when required ?
my plan was to just run them full bore as/when needed.
what happens when to them when i do that Charlie ?

They will still work, when the fans come on these draw a lot of amps & it hits the charging system pretty hard when turned on, the fan motors will also last much longer with the PWM used, I have the Derale one it works great, both fans are hooked together , when the ac comes on the fans come on at 60%, if the coolant heats up to much the fan speed will increase as needed.

I REALLY wish I would have moved my radiator like you are doing, I might do it at some point .

do you have a link to the controller ? [or one that will work]
i'm using a 90 [100 maybe] amp denso alternator, and the wiring has not been started yet.

not a great picture, you can see it lower right where the battery used to be, I mounted it on an aluminum plate to help keep it cooled off.

If you are running just 1 of the 2 fans for most of the time and both for AC, then run the fan closest to the bottom radiator outlet hose.

Cheap fan controllers add resistance to the fan system to slow and speed up the fans.

Pulse Width Modulation controllers send the full battery voltage to the fan but its done in millisecond pulses on/off so the fan has coasting time of no voltages. Its cleaner to your charging system and does not add any resistance.

Running both fans at 100 power is very noisy when they are switched on. The PWM's ramp the speeds so at 60% its much quieter.

thanks for the feedback guys ! really appreciated !

as to the derale controller, i found two part numbers, the one you mentioned, 16975, and a number 16976.
i tried to see any difference between the two, but the description looks to be the same on both.
i guess i need to call those guys.
Thanks Again !

You could always just copy the wiring and use the resistor diode pack for a 95-99 Ford Contour 2.5 V6 and the dakota digital control to make 2-speed fans.

I have the whole Contour fan setup on my car with the dakota digital controller, they are very quiet and it runs both fans at low speed when cooling is needed, switches to high when it hits the preset point. Or you could have a switch and use a cheap controller for the slow speed.

PWM is nice but can get spendy, and I'm not sure how reliable the controllers are.

The 16975 the one in the link I posted is universal & is the one you need.
the 16976 is a replacement one that comes mounted in their shroud

how reliable has your controller been ? i'm a ways from the wiring phase, but i have the fan coped into the core support now, fitting like it grew there.
i'm now fitting the radiator, and will fab brackets to keep it in place.
it will take a bit more trimming on the lower core flange to make it fit.
after that, i'll address the flex in the top of the core channel and the mods needed to be done on the hood latch brace.

So far it made it through the summer, & it gets VERY hot here in Southeast Tx, probably 2000 miles on it so far.

after reading a few reviews, i'm not sure what i'm going to do.
it seems more than several complain about the PMW controllers not lasting very long.
i might have to re-think my plan of attack. either go with a couple of focus/contour controllers, or explore the "hoosiewhatzit" mercedes fan controller.
i wonder how that one is working out ?

hoosiewhatzit controller is still working in my car. have one of the early ones and one of the later ones.
It probably has been running on it for over 5 years, however old that thread is. probably more as I lose track of time like that.
I have sent him some bug reports over the years and he has made improvements to prevent the issues I have seen from being blamed on his controller.

I don't know if it will work on those fans, you would have to ask him.
I would bet they are probably similar to the mercedes fans.