Surprise#2 and the subsequent scare
When it seemed that all was well, I'd taken out all the tools, and other items out of the car, cleaned the whole place up and was ready to put the seat back in place. Lo and behold, the seat wouldn't fit in place. Two issues
1. rails on either side weren't properly aligned (one was a little forward), and
2. the left rail was touching the top of the amp
No.2 was despite me doing a trial placement of the amp even before I started the job. I figured out that this was because I'd estimated a lower clearance for the cabling dressing, but that turned out to need more clearance. I tried shifting the amp a little towards the transmission tunnel but even in the end position, there was just a 1-2mm clearance between the left rail and the left edge of the amplifier. I decided to re-orient the amp in portrait mode.
Clearance check with amplifier in portrait mode
Amplifier re-orientation - connections W-I-P
Installation of amplifier in portrait mode
Disconnected the battery negative, and then reoriented the amplifier. This job didn't take too long and all was set again. I connected the battery negative and heard a pop. It seemed as though the circuit had drawn more amps. Went to the amp and found that it hadn't turned on. Measured voltage from the 12V power pin to the ground bolt and that was fine; so was the continuity from remote line to ground. I then pulled out the two 25A fuses and found both of them blown.
An act of stupidity that caused me a lot of pain and time
I'd already been getting quite tired of working on this project, and committed a blunder which even I am not able to explain why - in the absence of two 25A fuses, I wrapped some thin wire around one of the fuses and shoved the fuse in, only to be greeted by another pop and some minor fumes. I said to myself, " This is the end!". The main in-line fuse on the line from the battery had also popped due to this blunder.
Amplifier inspection and incident investigation
Disconnected the battery negative, took the amplifier home, and opened the end cover on the power side to observe for something amiss. Although I could smell that something had heated up, there was no damage on any path - equipment, solder, board lines. What I could not understand is what went wrong. After a while, when I was putting the panel into place, I suddenly realised what I'd done - while reorienting the amplifier, I'd hooked up 12V to ground and ground to positive.
How could I, who ensured multiple times to connect the speaker leads correctly, make an error in connecting the power and ground? Two theories:
1. From the earlier evening, I'd forgotten to pick up my stuff after paying for it at a grocer, at a bakery, and at a veggie shop. Mind wasn't working at its best
2. My earlier amplifier, the Kenwood KAC-8401 had the 12V point at the outer end followed by ground followed by the remote power. Was this a case of primacy bias? No idea.
Installing the amplifier back, test run, and final installation
All I could do under the circumstances was to install two new 25A fuses, a temporary
jugaad in the form of a 30A blade fuse, and check if the amplifier powered on. It did and I heaved a sigh of relief. After the amp powered on, I connected the front channels first and both speakers fired. Subwoofer followed next on the rear channel in bridged mode and even that worked fine. The next task was to get the AGU 40A in line glass fuse.
Temporary 30A blade fuse for testing
Searching for an AGU 10X38mm fuse
I must have asked at no less than 20 places (electrical, auto electrical, accessory stores) to no avail. Two accessory stores did say that the whole set was available (the fuse inside the fuse holder) but that's not what I wanted. Eventually rode with someone to SP Road, and got the 10x38mm fuse in the ceramic avatar, rated for 32A.
Finally!
It was a perfect fit, and once lined up, the equipment all worked as intended. I ran the system at various volumes just to check if the in-line fuse heated up or whatever. All was well. Amplifier secured, seat in position and tightened, and all was well.