A Few Basic Vehicle Install Questions

[N6LAU]

I'm going to be installing a new radio in my vehicle and I have a few basic questions I'm unsure of the answers to. Radio is a UHF CDM1550LS+ and the vehicle is a 1997 Toyota Corolla w/ manual transmission.

Is it better to run the negative wire to the negative battery post or should you go directly to the body of the vehicle? Also should a fuse be used on the negative wire? What are the pros and cons of these?

[Jim202]

I'm going to be installing a new radio in my vehicle and I have a few basic questions I'm unsure of the answers to. Radio is a UHF CDM1550LS+ and the vehicle is a 1997 Toyota Corolla w/ manual transmission.

Is it better to run the negative wire to the negative battery post or should you go directly to the body of the vehicle? Also should a fuse be used on the negative wire? What are the pros and cons of these?

You will probably get a number of different answers on the fuse in the negative wire. Those that say to use the fuse are supporting the idea that the ground wire can carry the high current of the starting motor under the case of the battery ground wire to the frame going bad. The comment I have to that is you will know there is a problem long before radio damage as the vehicle will have starting motor issues. Second comment is that the antenna coax shield can be a path for the high current through the radio and the black wire going to the frame. Again I have to take the stand that you will know there is a problem long before the radio takes the hit.

Anyway, I have been in this business for well over 45 years now and have not seen one radio damaged by the vehicle starter motor high current. This goes for a very large number of fire trucks, ambulances, large trucks like Macks, Freightliners, Autocar and the list goes on.

The major radio vendors like Motorola, RCA, General Electric, and the rest of them have never supplied a fuse in the negative or frame ground side of their power wiring. You can read a bunch on the subject and get all sorts of answers to your question. My position has always been if there was such a large problem, the big radio vendors would have been supplying the ground fuse way back in day one. That has never happened. They do supply a huge number of mobile radios to the public safety and federal government. If there was a problem as some like to cast over the subject, these radio vendors would have taken action years ago.

I will say that sure there is always some dumb boob that has ignored a problem with the vehicle electrical system and caused some damage, but the signs of a problem were there long before any damage was done. Like he had problems trying to start the engine, battery wires falling off, have to get a jump start all the time and the list goes on.

Jim

[FireCpt809]

Ive been installing CDM's since they came out. Ground it to the chassis. We use a heavy duty sheet metal screw and star washer. Its usually grounded in the passenger side kick panel behind the trim. I have never fused a ground.

[Batwings21]

If your grounding to the chassis (which is normal) then no fuse should be used in the ground wire. If you were to go directly to the battery then I would use a fuse, the reason for that is you could get high current draw from the antenna ground through the radio and neg wire back to the battery IF the chassis ground from the battery were to fail or become corroded.

[Wowbagger]

IF you are going to the battery THEN you should have a fuse. This "you'll see the problem before it damages your radio" is foolish - a cheap fuse and holder vs. the possibility of blowing up your radio.

Now, if you are grounding to the frame, you don't need the fuse on the negative, as your radio won't be a potential path for current.

So, why ground to the battery rather than the frame? The idea is that taking power directly from the battery will be lower noise than taking power from the frame: the resistance of the battery is much lower than the resistance of the battery + frame, so a given amount of noise current will create a lower noise voltage. However, most of the noise in a vehicle is lower frequency - as in HF - rather than higher frequency (VHF/UHF/800MHz). If you are installing an HF radio then going to the battery may reduce the amount of noise the radio picks up from the vehicle. For higher frequency radios (VHF and above) it likely makes no difference.

[Bill_G]

Put your ground where Toyota puts the battery ground on the body inside the engine compartment (or at least on the same piece of sheet metal). No fuse required since it is a chassis common ground radio in a neg ground vehicle. This will give you the quietest ground possible, and the least opportunity for a return through the radio.

[N6LAU]

Thanks guys, this is all very helpful info. Sounds like I will be running the ground wire to the chassis.

Question... How do I find where the battery ground is located in the engine compartment? I've looked around but can't find a definite location.

Also when I do find the location I was planning on putting a ring terminal on the end of the negative wire and then using a sheet metal screw to tack it down. FireCapt mentioned using a star washer. Is this necessary also and what is the advantage?

[FireCpt809]

A star washer will scuff the paint and make better contact. If you just use a sheet metal the only contact with the chassis is the metal where the screw actually goes into the chassis against the terminal. More metal to metal contact for a better ground.

[Bill_G]

Look around again. There are generally two leads off the batt neg - a large one to the starter and a small one for the electrical return. The small lead usually isn't very long. I am not familiar with Toyotas. They may return to the starter though that doesn't seem prudent. A previous owner may have replaced the batt leads and never hooked up the body ground. But, it is usually someplace fairly easy to get to - either on the fender, or on the radiator mount. Ford uses a green self clearing screw in a stamped threaded hole. If you cannot find a body ground, you can make one. Try to put your sheet metal screw through a double layer, like a welded seam, to give you greater mechanical strength. Scrub the paint, lay down the star washer, then the ring lug, and fill it with the screw.

[N6LAU]

Okay, update. I found the piece of metal that the battery ground went to and ended up sanding the paint off exposing the bare metal in the area the radio ground was going to go to ensure good contact between ring terminal and chassis. Drilled a hole, fastened the ring terminal to the chassis with a sheet metal screw and life is good.

Now that power for the install is taken care of I'm considering whether or not to ditch the NMO mag-mount I'm currently using and go for the 3/4 hole NMO mount. Not too sure on how I would neatly route the coax if I did that but I definitely like the idea of having good ground to the NMO mount as opposed to the magnet. I do have a sun-roof just forward of where I feel would be the ideal spot for the mount but I never use it so don't mind if it's rendered unusable. Anyone have any advice on how to possible go about this?

Joe

[Jim202]

Okay, update. I found the piece of metal that the battery ground went to and ended up sanding the paint off exposing the bare metal in the area the radio ground was going to go to ensure good contact between ring terminal and chassis. Drilled a hole, fastened the ring terminal to the chassis with a sheet metal screw and life is good.

Now that power for the install is taken care of I'm considering whether or not to ditch the NMO mag-mount I'm currently using and go for the 3/4 hole NMO mount. Not too sure on how I would neatly route the coax if I did that but I definitely like the idea of having good ground to the NMO mount as opposed to the magnet. I do have a sun-roof just forward of where I feel would be the ideal spot for the mount but I never use it so don't mind if it's rendered unusable. Anyone have any advice on how to possible go about this?

Joe

Again I am surprised that there haven't been all sorts of comments on how and where to mount the antenna on the roof. Best advice I can offer is see if you can get the edge of the head liner to open up enough to shine a flashlight up in there. Look around and see what you have for braces and the like. You don't want to drill into a brace. There should be a track where your sun roof slides back into. You want to be to the rear of that. You can come down one of the side posts of the vehicle. It may take some doing to get the cable to run down to the floor. Be careful of any side post airbag items if your vehicle has such items.

Once you have the coax down at the floor level, you can run it to the radio. If this is a dash mount, then the best place to run the coax is in the side channel at the door. Normally the plastic either has a few screws or it just pops up. The exact details will depend on the vehicle design.

Good luck on your efforts.

Jim

[wa6ylb]

Okay, update. I found the piece of metal that the battery ground went to and ended up sanding the paint off exposing the bare metal in the area the radio ground was going to go to ensure good contact between ring terminal and chassis. Drilled a hole, fastened the ring terminal to the chassis with a sheet metal screw and life is good.

Now that power for the install is taken care of I'm considering whether or not to ditch the NMO mag-mount I'm currently using and go for the 3/4 hole NMO mount. Not too sure on how I would neatly route the coax if I did that but I definitely like the idea of having good ground to the NMO mount as opposed to the magnet. I do have a sun-roof just forward of where I feel would be the ideal spot for the mount but I never use it so don't mind if it's rendered unusable. Anyone have any advice on how to possible go about this?

Joe

Again I am surprised that there haven't been all sorts of comments on how and where to mount the antenna on the roof. Best advice I can offer is see if you can get the edge of the head liner to open up enough to shine a flashlight up in there. Look around and see what you have for braces and the like. You don't want to drill into a brace. There should be a track where your sun roof slides back into. You want to be to the rear of that. You can come down one of the side posts of the vehicle. It may take some doing to get the cable to run down to the floor. Be careful of any side post airbag items if your vehicle has such items.

Once you have the coax down at the floor level, you can run it to the radio. If this is a dash mount, then the best place to run the coax is in the side channel at the door. Normally the plastic either has a few screws or it just pops up. The exact details will depend on the vehicle design.

Good luck on your efforts.

Jim

If you find that your coax run is getting rather short, you may be inclined to make a short cut across the floorboard carpet to the radio. Do your self a favor and check underneath the floor board to find out where the exhaust and or catalytic converter is located. We have seen many coaxes become shorted by heat from either the exhaust system or even the floor heater blowing on the carpet. (you can tell where a shorted coax has melted by running the cable through your fingers in an arc - the melted area will feel "stiff" for a few inches). In central California, where it gets to plus 100 degrees in the summer, we had to go with Teflon based coax to keep it from melting under the floor mat!. (The short occurs when the cable itself gets hot and the center conductor "drifts" in the center conductor insulation, eventually shorting to the shield). If you live in an area where it doesn't get too hot and or have avoided all the heat sources from below the floorboard, then you can get away with using the black colored coax cables. If you have many extra feet of coax cable left after making it to the radio, cut it off, leaving a bit extra to connect the cable at the radio. Coaxes for mobile radios tend to be rather lossy (UHF and 800 Mhz for sure), and the shorter it is (within reason), the better off you are.
B.

[smokeybehr]

One of the problems with vehicle install cable is that it's almost always RG-58, which is fine for most installations, but if you go with power over 50W or freqs above 440, it loses a LOT of signal. Kick down the extra money for RG8x, LMR200, LMR240, RG-141/142, or RG-223, with RG141 the best for microwave (=>900mhz). RG-141/142 is the same size as RG-58, so all of the hardware is the same.

I have replaced the RG-58 with RG-8X on a lot of the mounts that I use, especially if I'm salvaging a mount that has a short piece of coax, or I need something longer than the stock 5M/17' length. I also add a little heat-shrink tubing to help the mechanical strength right at the mount. It's a foam dielectric, but I don't run anything under floormats, except along door sills.