TUTORIAL:

MFJ-1126 Radio Power Distribution System Installation

1999 Jeep Wrangler

MFJ Enterprises

300 Industrial Park Road

Starkville, MS 39759

662-323-5869 Voice

662-323-6551 FAX

www.mfjenterprises.com

Getting power to all of the radio and other equipment was a bit of a concern, but nothing that could not be resolved quickly. This Jeep came from the factory with an upgraded electrical package. The upgraded alternator is rated at 117 Amps. We eventually replaced that with a really nice alternator from Wrangler NW, and a dual battery system as well.

A Warn HS9500i winch was already installed when we got this Jeep. Good amateur radio practice says that you should fuse power cables as close to the battery as possible. However, the cables for both the inverter and the winch are not designed to have a fuse in-line, and the manufacturer instructions indicate not to install fuses on those lines. Considering that they can draw over 100 Amps (fuses larger than 100 Amps are very hard to find), that they are internally regulated, and that their cables are very heavy and have hefty insulation, fusing them at the battery simply isn't practical.

The alarm system and the ARB Air Compressor are also directly connected to the battery. They were previously installed and have fuses in-line, but further from the battery than I might like to see. We corrected those as soon as we were able. 

We used Anderson Power Pole connectors on all of our power wiring for the radios and other products we added. I even went through and put them on the electric door lock wires that were previously installed. If you are not familiar with these power connectors, they are used heavily by HAM radio operators. They are capable of handling a lot of current, are self cleaning, and are easy to use. There is more detail on them in the manual for the MFJ-1126 - which you can download via the link at the end of the article.

I wanted a good way to connect all of the gear we were installing to the battery, and to make an organized power center. With the work we did in the glove box installing the Cobra Inverter, we had plenty of room still available in there. I just needed to find a good box with a bunch of Anderson Power Pole connectors. I didn't have to look far.

MFJ makes all sorts of neat accessories for HAM radio, many of them very specific niche items. They also have a set of power junction boxes pre-wired with Anderson Power Pole connectors. We needed connections under the dashboard for the following units. I have also listed the maximum current drain for each unit.

The Whelen PAP112 was connected to an auxiliary, always on, 10A power circuit in the Jeep. It draws a maximum of 8 Amps, so we didn't include it in this part of the installation. This power installation relates only to radio-related gear. The radar detector is a radio receiver, that's why I included it here.

Assuming that we had everything connected via the Anderson connectors running at maximum power, we would be drawing a total of 39.05 Amps. I don't see this happening - but the potential is there if we have ALL of the radio gear running at maximum power. I don't think I have ever seen the 706MKII-G come up to 20A, and I know that the others all normally run well below their rated maximums.

We would need space for 8 devices at 39.05 Amps. This requirement fit perfectly with the MFJ-1126 (8 devices at 40 Amps). We just had to make sure that there was enough room to fit this in the glove box area. The 1126 measures 9" long. That was also perfect, we had about 1 inch to spare.

The unit comes with 6 feet of 8 AWG cable. It is already connected inside the MFJ-1126 and comes out through two grommeted holes. There are connecting rings attached at the far end. It also has a separate ground terminal.

I metered everything out, the ground terminal is electrically connected to the case, the negative power wire to the battery, and the negative terminals on the Anderson connectors.

It was easy to pull the attached power cables through the dashboard and firewall, and it made it to the battery without stressing the cable at any point. It literally fit just right.

I was interested to note that it does not include any fuses near the battery terminals. It does have a 40 Amp master fuse on the unit to the left, but no in-line fuses near the battery terminals.

Since this is only a 40 Amp circuit. I was able to solve this with a quick trip to the local Wal-Mart. Whatever you think of them, they are often handy for certain things. They sell automotive stereo amplifiers. That does nothing for us, except that they also sell the accessories to install automotive stereo amplifiers - including in-line fuse blocks and fuses rated up to 100 Amps. The product line they carry is from Scosche, and for under $18.00 you can pick up two in-line fuse blocks that include both a 40 Amp and an 80 Amp fuse each - take your pick.

We cut the cables close to the battery, stripped back a bit of the insulation, and installed these fuse blocks with the 40 Amp fuses. Good amateur radio practice says that you fuse BOTH positive and negative cables as close to the battery as is practical and possible. It may be overkill to fuse the negative side, but we did it anyway.

You can buy replacement fuses for these fuse blocks at Wal-Mart. We keep a big fuse kit with all sorts of fuses - including Euro, American, and Japanese fuses of all sizes. They can be used to replace fuses in our Jeep, to help others during drills or emergencies when they blow fuses, or during a motorist assist call if on duty. You never know, and the Boy Scouts really are right - Be Prepared!

The hardest part about mounting the MFJ-1126 was deciding exactly how to mount it. We kind of had to work backwards - figure out where can we put it so that the wires will be out the way - then we made the connections.

Because of the position of the factory fuse block (center/back of glove compartment) and the location where we mounted the inverter (bottom/front of glove compartment) we needed to mount this in the top of the glove compartment. There is plenty of space up there, BUT there is a problem.

Above the glove box is a big metal box with lots of flat area on the bottom of it (the top of the glove box). The problem is that the box is the passenger side airbag housing. Putting screws into that would be a bad thing - but it was the ideal spot to mount he MFJ-1126.

To solve this we elected to use the real industrial velcro - hard side on the bottom of the box/top of glovebox, soft side on the bottom of the MFJ-1126. The real industrial stuff has a high-temperature-compatible adhesive, and it holds on tight.

With this arrangement, the MFJ-1126 can be easily pressed into place, but it ends up being upside down. That doesn't hurt it, but it means that we have to pull it down to see the voltmeter on the front of the unit. That's not too bad - we won't be using it under most circumstances. If we need to see it, we can easily pull the unit down.

Once we figured out where it was going and how we would mount it, we needed to figure out the routing of the power cables we would be plugging into it. They had to be organized, and had to be clear of the inverter when the glove box door was closed. They also had to have enough slack to allow us to pull the MFJ-1126 out to where we could work on it and see the meter with everything plugged in.

The following photo may not look really pretty...

But it looks rather good when it is installed and the wires are slipped behind the AM/FM radio antenna cable. It holds them securely out of the way of the inverter, and they can be moved to the side easily to facilitate access to the fuse box.

For additional wire management, we used zip-ties to secure the wires together in a logical pattern that unfolds when the unit is removed to work on it. This works fine, and supports them well out of the way of the inverter when the glove box door is closed.

Note the connection I ended up using for the Lowrance iFinder GPS. The GPS takes 3 volts, so the cigarette lighter plug they include with their combination power/RS-232 connector (they use a combo jack for both NMEA output and power) has electronics to reduce the voltage. We took it apart, removed the fuse, and wired an Anderson Connector to the unit, and put it back together. The fuse it is plugged into on the MFJ-1126 is a 1A fuse. Again, sometimes you have to think creatively.

We put the 706MKII-G, D700A, and Uniden BC-796D Scanner (all of which are secured in Tuffy locked units) on the 3 unswitched outlets that are pictured above using 25A, 15A, and 1A fuses respectively. These three are rated 40A total, and the maximum possible draw for these three units should be 32.2 Amps.

All of the other items (CB radio, radar detector, Lowrance iFinder GPS, and the connections for the TNC and the guest HT radio power) are on the 5 switched outlets pictured here....

Some might ask what benefit the switched outlets are in this particular installation. If we have the vehicle on display or in a situation where we don't want someone playing with certain items like the CB, we can open the glove box, reach in and hit that switch, and then close it up and lock the glove box cover - another benefit of keeping that cover. It's fast and easy. Not really a necessity, but a nice thing to have.

Directly above the switch for the switched outlets is a DC voltmeter. Not a real necessity in our installation, but still a handy thing to have.

MFJ gives you everything that you need with this unit. Aside from having the power cables already attached, they also give you a bag with a bunch of pairs of Anderson Power Connectors and extra fuses of various sizes. That is handy, and we were able to get our installation just the way we needed it using only what came in the box with MFJ-1126 and a few zip-ties from AutoZone.

All in all, this made for a great power system. It is fused, protected, and clean in appearance and function. It supports all of the radio gear that we have installed - which is about all that can be physically installed in a Jeep Wrangler - and will support whatever gear we use as replacement equipment in the future.

The MFJ-1126 is yet another one of the many cool products from MFJ. They have products to solve a lot of problems. The MFJ-1126 made the power installation for our Jeep that much easier, and it is very well made. I was impressed. I was able to test ground continuity from this box to every other metal part on the vehicle - including both of the Tuffy Security Consoles we installed. It could just as easily be used in any other mobile installation, and they are just as functional in your home station. I plan to use this unit, or their smaller ones, in any mobile installations I work on in the future.

-- James Bell Jr.