There's a pattern in the FJ modification projects I'm undertaking – they always seem to expand into bigger, more complicated projects than I initially expected them to be.
A current project provides a great example. I'm installing a CB radio. How hard could that be? It's a small box with two wires coming out the back (power and antenna). Easy, right?
Well.
Where do I mount the thing? In the cramped interior of an FJ, there's really only one place that we liked: on the ceiling, in the middle of the car (between the driver and passenger). That way we can both use it, and it's out of the way of both us and the airbags.
That means I have to take the headliner out (the “headliner” is the fuzzy-coated plastic piece over your head when you're sitting in an FJ). It was not obvious how to do that, so I bought temporary access to the online shop manual to find out. The good news: one can remove the headliner with just the tools I already owned (one slightly special tool is involved: one that makes it easy to pop off the special fasteners used on many interior parts). The bad new: removing the headliner requires
first removing most of the interior of the FJ – something like 50 plastic and metal parts. That took an entire day.
The antenna is mounted on the rear door hinge. That means the antenna wire has to be routed through the rear door – and that means the rear door has to be disassembled. Compared to the headliner, that's easy – but still, that took another hour.
Then I discovered that there's a 1.5" gap between the headliner and the actual metal roof. I could fill that gap easily with a piece of 2x4, but how do I fasten the 2x4 to the roof? Some research gave me the answer: install powerful magnets in the top of the 2x4 piece, and use glue. The magnets act like a clamp to hold the piece to the roof, so I don't need to make any holes in the roof.
It took me nearly a day to route the antenna wire just 12 feet. First I had to get it through the door, which is accessible only through an awkward hole. Then I had to route the cable through a pre-existing rubber “boot” that holds all the
other wires going to the door. Naturally, that boot is almost full of wires, so snaking the antenna wire through there was a challenge. Then I had to route it around all the bits of framework and around the side “curtain” airbag mechanisms, attach it to the roof, and get it over to where the CB radio would be mounted. All of this work was overhead – not my favorite :)
Then I needed power to the CB. The radio came with a 6' long power cable, with an inline fuse holder just 8" from the radio. A fuse holder under the headliner seemed like a really bad idea – I'd have to disassemble the FJ just to
check the fuse! Plus the 6' cable wasn't nearly long enough – it's 10' just to get under the dashboard.
Where do I get power from under the dash? More research in the online shop manual convinced me that I really didn't want to even try that; it was better to be in the engine compartment, so I'd have a place to mount a “real” fuse holder. That means 14' of cable. The original power cable is 28 gauge copper, just barely big enough to give an acceptable voltage drop at 6'; too small for 14'. So I upped it to 14 gauge (overkill, but cheap), spliced it right next to the connector that led into the radio, and routed the cable into the engine compartment.
Now I needed power. That's easy, right? Battery is right there! But wait...I don't want the CB to work when the car is turned off; leaving it on accidentally might drain the battery. I want power that's on only when the ignition is turned on. But that doesn't exist within the engine compartment, at least, not in any obvious way. Back to the shop manual. It turns out that there are two places I can find power that's switched by the ignition: one for the ignition coils, and one for the fuel injectors. However...both of them are fused for just their intended purpose, not for my CB. So I need a relay that turns on and off with the ignition coils, and a circuit that senses the ignition coil power without drawing any significant current from it. That's something I might want for other purposes as well, so I fused the relay input for 30 amps, and I put a secondary 3 amp fuse in for the CB. The engine compartment is starting to get a lot of wires :)
And that's all just for the CB! I have a bunch of electrical projects to do: CB, roof-mounted headlights, dual battery system, 2KW inverter, and the on-board air compressor. I'm quite likely to have other things down the road as well. So all the under-the-hood stuff I built to be easily modified and extended – but of course that adds even more work.
Projects are ever-expanding...
So I designed and built a little circuit to solve this problem. It detects that the engine is running by sensing the battery voltage. When the engine is not running, the alternator is not running, and therefore the battery voltage will be something less than 12.8 volts. When the engine is running, the alternator is also running, and the voltage will be variable, but certainly over 13 volts (as measured in the FJ, it's generally over 14 volts. So a simple comparator circuit, com)paring the actual battery voltage to 12.9 volts, does the job quite nicely. The comparator's output drives a MOSFET relay driver, and the relay provides 30A that's on only when the engine is running. Since I was going to this trouble anyway, a minor addition also provides a separate output that is on whenever the ignition is on. This duplicates something already in the truck, but it does it with a separate relay and fuse – better than tacking it onto the stock system.
Here you see it all installed. I put a pair of LEDs on the front, more for testing than anything else. The relays are the four little cubes off to the right.
