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We needed a place to install the cooling fan relay box.The Littelfuse housing that we selected to switch the power to the cooling fans needed to be located near the fans. This spot underneath the blow-off valve and behind the coolant expansion tank seemed like it would be good enough.
Sometimes I think Tom’s favorite pastime is drilling holes into perfectly good cars.
The Littelfuse HWB18 enclosure comes with a nice mounting bracket. Just bolt it in and then the enclosure slides onto the bracket. The enclosure uses a retention clip for securing it to the bracket.
You can see in the corner what the assembly looks like when it’s slid onto its mount.Tom is digging around trying to install both the ground as well as the main power that comes from the starter positive. Remember that we are feeding the cooling fans via a fuse/relay system that gets its main power from the starter, which gets its main power from the contactor that is the main cut-off for the entire car.
Battery -> contactor -> Racepak supply -> starter -> cooling fan relay assembly.
Got it?
Also note that the Haltech Elite 2500 ECU is what’s going to be controlling the cooling fan operation. When the Haltech decides the engine temperature is too high, it will engage the cooling fan. However, ECUs generally want to switch to ground when it comes to actuating relays. In other words, they want to sink current, not source current.
That meant that we needed to have constant power to the coil side of the relay, and then the Haltech ECU would ground the other side of the coil, which would engage the relay. This also means that you want the fuse on the high/positive side of the relay coil. Why? If for some reason the relay coil shorts out internally to ground, the fuse will blow. If the fuse is “after” the coil, and the coil shorts internally, then your fuse does nothing and your relay melts.
Remember: ECUs switch ground for driving digital circuits.
