Car that Goes Boom - Part 2

Continuing the fun from the last post about the amplifier install into Oliver. When we left off, we had selected an amplifier and an install location. I had concocted and fabricated brackets to support it, installed the amplifier and did some tests, both by sitting near it as well as a road run to verify the brackets held. Today, I will go through the wiring aspect and fire this thing up.

Wiring Rear

In the last post, I mentioned there are 2 methods for wiring signal to the amp. I used the pre-amp / RCA cables method. To achieve this, I first needed to find and label 6 RCA cables. I found a few old RCA cables from my A/V stash, but they were over a meter (4 feet) long. On each wire, I marked a (F)ront, (R)ear or (S)ub prefix and (Left) or (R)ight. I did this on both ends. Why? So no matter which end I was doing maintenance on (or replacing a component) I knew what the wiring was without having to jiggle wires or unhook the other thing to figure it out. On the amplifier end, I plugged the cables into flat 6-pin pigtails, keeping the F/R/S wires together. Next, I pulled the stereo out of the center console, and passed the RCA cables through. There are a few wires that need to be removed from the big plug in the back of the stereo, and the rest remain. Simply: all of the speaker wires need to be removed from the plug. Consider, the "signal-on" wire needs to be made available to the amplifier. I had not used it at this point, so I needed to add an extension so it would reach. With the RCA cables plugged into their correct holes in the stereo, the power, switched power, ground and "signal-on" wires connected, the stereo can get put back away. Last, I plugged the 6-pin plugs into their respective slots on the front of the amplifier, noting that "(F)ront" goes to channel 1/2, "(R)ear" goes to channel 3/4 and (S)ub goes to channel 5.

There is a 4-pin for the remote bass and "signal on" as well. The remote bass is a knob that I will install later. For now, it is tucked behind the center console near the driver side foot well, but it is wired. The signal on wire I had located was connected to this pigtail and heat-shrinked. To keep things clean, I zip tied the bundle of cables and wire together, and tucked them into protective wire wrap (like this) I picked up at Harbor Freight. The black wrap made the cables disappear. I routed the whole thing up and over the top of the amplifier before routing it behind the center console. This should keep the bundle out of the passenger's feet while still keeping the controls available for fingers.

Wiring to Speaker Box

clamped screwdriver as wire spool

Up until now, the wiring going to the rear of the car had run through the cockpit. I ran the 2 wires along the transmission tunnel on the passenger side. Now that I was adding another pair of wires, though, the cable had become too thick, and was making a lump under the carpet. So, I decided to route the speakers under the car. Again, leveraging protective speaker wrap (smaller diameter this time), I routed the wires for the 2 rear speakers plus the sub woofer to the front of the car through a wiring feed hole (mostly hidden by the sub box). I think it used to control the fuel pump because it has spade connectors in it. From there, the cable ran along the underside of the car with the other bundle of wires that run front-to-back all the way from the fuel pump to the starter.

Because of the location of the wiring hole in the trunk, I did not leave much slack in the wires back there. Instead, I considered ways I could get the wire bundle to stay up against the box. I decided to leave the cable wrapped almost all the way to the sub-woofer plug, and figure out how to tidy it more later. With the other ends of the wires for the speaker box hanging under the glove box, I was entering the final phase.

Wiring Front

$3 wire wrap protects

Out the back of the amplifier are 12 threaded-bolt wire mounts: +/- for both front (4), +/- for both rear (4), a pair for the sub (2), and one each for ground and power. Since I had done everything else so cleanly, I didn't like the idea of running a bundle of wires at the amplifier. For maintenance and ease of amplifier removal, I wanted something easier. Also, the only slam on this amp in the reviews was about these connections, so I wanted it to be set up once and then forgotten about. So, I got some multi-wire connectors from BritishWiring.com. With these connectors, it would almost look like it was part of the original MGB. Unfortunately, they don't sell any even numbered pins, so I used a 9-pin for the front/rear speakers and a 3-pin for the sub. I wired a few inches of wire from the amplifier to the male plugs (see the second picture from the top) and then wired the speakers and ground/power into the female plugs. That sentence was quick to write, but it took me a several hours of effort.

Wiring Power and Ground

Test fit - RCA cables too long

All I had left was the ground and power. I had intended to use the extra pin on the odd-numbered plugs. When I set out to do the wiring into the plug (see top picture) I quickly discovered that the 10 gauge power/ground wire needed for the amp were very different animals from the 14 gauge speaker wire I had in the rest of the plug. Quite simply: the 10 gauge was too thick to pin. So, I bought a 3rd 2-pin plug designed for a GM alternator from the local NAPA. It had male and female plugs on it, so I could cut it into two pieces and continue the plan. Similar to the other plugs, I put the male end on the amplifier side and wired the female end into the car. With a ring terminal on the black wire (ground), I leveraged the rear bolt from the amp mount. This was a solid ground, based on my connectivity and voltage tests. For the power, I ran a blue wire from the alternator, through a 10A bladed fuse and through the rubber-lined wiring hole in the firewall behind the glove box. This dropped the power supply nicely near the amp.

Once both were connected through to the plug, I was ready to plug everything in for a test. I think, ideally, it would have been better to wire the power into the battery, but the battery is behind the seats, so the wire run would have been longer, creating a greater likelihood of a short. I ran a couple connectivity tests to make sure everything was set to go, and then re-connected the ground on the battery.

Test Fire
I had already identified a couple of things that needed to be changed, but with everything hooked up I wanted to see if it worked before I started changing things. So.. in short, the speaker wires were moved from the head to the amp, the amp was wired with power and grounded, and the power-up signal from the head was routed into the amp remote switch. Everything should be set to go. With the battery still connected to a tender, I slapped the face back onto the head unit and turned it on. All the lights came on, but I couldn't hear anything. I turned the stereo way up and could barely hear sound, so I concluded the gains on the amp were too low. Second attempt: turn the stereo back down to single digits and turn up the gains. Now we have sound.

With Rush's "Spirit of the Radio" cranking, I set the various levels so Getty Lee's bass snapped and growled, Neil Peart's drums punched and Alex Lifeson's guitar sang. It sounds so good inside the cabin with the top up. Once I get out, the sound really doesn't travel outside of the car as much as I would have expected. Of course, once the top goes down, things will change. This leaves one last test: driving at speed with the top down. That will have to wait until Summer. In the meantime, I tried the classical station for a different sound signal and it sounded really good... but not as good as Rush did. There's just something about Rush. Maybe it's the punchy bass. Whatever it is, the next test will be an early Dead show, like, maybe, the Music Box from Feb 1968, and then a wall-of-sound show.

Thanks for following along. I still have to install the passenger seat into Oliver, and then I may start working on the interior door panels. Or, maybe, I'll just finish the trunk. I don't know. I'll see how I feel when I get to the garage.