Although I was originally considering putting the heater in the rear trunk near the controller, after further reflection, I decided to put it in the passenger compartment, below the dash, between the driver and passenger. The main reason was to simplify the wiring. A secondary reason was that the heater did not fit especially well in the rear trunk. First step was attaching the heater mount to the firewall. I used rivets:
I then mounted the heater on the mount. I made sure when placing the mounting point that the heater did not interfere with any of the pedals or the steering linkage (it's hard to tell from this picture, but the steering linkage is not all that close to the heater blower):
I used 10-gauge red and black wires to deliver power from the 144-volt pack to the heater. I routed them through the original (now useless) windshield sprayer hose grommet:
Next up was work in the middle compartment. I mounted a power post so I could attach several negative cables (the original negative cable from the most-negative point, along with negative cables to the charger and to the heater):
Next, I took the contactor I ordered...
...and mounted it on a piece of polyethylene along with the large fuse which protects the 144V heater circuit:
I hung the board from the middle battery box using tie wraps (also visible in this picture are the three wires going to the negative terminal post):
I then ran a yellow wire from the +12V input to the contactor to the switch location on the dashboard. I also ran a brown ground wire from the contactor to the grounding stud in the gas tank compartment. Note the yellow rubber cap on the negative post - I have a story to tell about that down below...
Here is the switch that will go into the dash to control the heater. The red wire goes directly to unswitched +12V (because I want the heater to be able to run without the key in the ignition). The yellow wire is split to drive the contactor and a relay for the heater blower motor in parallel:
This is the relay - a standard 12V 40A automotive relay, normally open. The yellow wire is from the switch above, the red is directly from unswitched +12V (I used 12-gauge wire since the blower pulls a fairly large current). The brown wire ties into grounding wires behind the dash. The black wire is +12V power for the blower, and the orange wire is ground for the blower:
Here's the wiring around the heater - I wrapped the contacts of the relay in electrical tape (to avoid shorts) and tucked it up above the heater:
It all works pretty well. You turn the switch on, and hot air blows out of the heater. Originally, I was going to attach hoses from that to the original heating system. However, I tried that, and the warm airflow was unsatisfactory. Fortunately, the heater is well-positioned to keep my feet toasty. I may install the flappers that came with the heater so the driver and passenger can independently control airflow.
Last, here is a wiring diagram of the heater circuits. Originally, I had the contactor and relay in series with the switch. However, this led to an excessive voltage drop which meant that the contactor did not close. So, I changed and wired them in parallel as shown here:
Remember the yellow rubber cap on the negative post I was telling you about? This is why it is here. I was tightening the bolts on the most-positive post, but my normal electric-tape-wrapped wrenches (that I use on the batteries) were not the right size for that bolt. So I used just a plain wrench. I managed to brush the top of the negative post while the wrench was touching the positive post. It resulted in a most exciting spark, including blast damage around the positive post and a flash burn on my hand that was holding the wrench:
Moral of the story: be very careful when working with high voltage... If you think you are being careful, think again, and find another way you can be even more careful. I was very lucky not to have damaged myself more than that flash burn on my left hand. I really need to get around to purchasing and installing that high current circuit breaker I've been thinking about...