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Something to think about

Discussion in 'Mobile Radio Systems' started by K0BG, Jan 21, 2019.

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  1. AI7PM

    AI7PM Ham Member QRZ Page

    From Ford. Though I think this one was from the 11 or 13 year, it applies to multiple years. I have always only gone to the battery for the positive. Interesting that the ham gear handbooks still promotes the fused neagtive to battery nonsense, and even using their flimsey wire that is unsuitable for the under hood environment. Yet, look at Motorola, Harris, etc. and you find commercial and public safety gear instructions to ground to chassis as close as possible to the gear.

    Attached Files:

    KD5BVX likes this.
  2. WB2LBV

    WB2LBV Ham Member QRZ Page

    If there is a sensor on the negative terminal of the battery, the one thing you do NOT want to do is connect your negative/ground cable directly to the battery terminal. Doing so will result in the sensor being bypassed and the battery connected straight to ground/chassis. This will cause issues with the vehicle electronics and may affect the charging system and set trouble codes. Use a good chassis grounding point instead.
    AI7PM likes this.
  3. KF5LJW

    KF5LJW Ham Member QRZ Page

    You are correct a fused negative at the battery post is long antiquated and can be dangerous. I started my career at a electric utility communications department in 1979, and even then the negative battery return was always connected to chassis, and fused battery directly on the battery term post. I left the utility and went into Telecom to make my career. Well today I have made full circle and back with the same utility that has grown tremendously with mergers and now that utility operates in 12 states and my job today is designing a extremely large P25 Phase 2 radio network using Harris radio products. The company auto fleet is over 1200 vehicles with over 20 radio shops through out the network. I work a lot with the field guys which some are hams.

    OK here is what I am driving at. The radio guys have most of the major auto manufactures, even Japanese and Euro's electrical diagrams and documentation. I have talked with the techs who do the installs and looked at the documentation. What they have access to is not available to the public in general. They have the documents for Law Enforcement radio installs. Most have pretty much universal instructions with some minor exceptions. However there is one thing in common with all manufactures with respect to the Negative Battery Return. Without a doubt they all recommend connecting directly to the chassis at the nearest hard point which may or may not be under the hood. most likely NOT. Most radios are installed under the seat, behind the seat in Trucks, or dash mounted. There are a few reasons for this most notable is all the manufactures run a bonding strap with the factory wiring harness and it bonds to the chassis at various points as it works it way back to the rear taillights. This forms a Equipotential Ground Plane which means you will have both extremely low resistance and impedance. In other words will minimize voltage loss on the dc battery return and minimize noise. Running battery return back to the engine compartment is counterproductive and will result in poor performance.

    The chassis hard points are pretty easy to find. You find them by finding the wiring harness and look for where the harness is bonded to the chassis like under the front and rear seats, or behind the dash board. The nonsense about galvanic corrosion is moot point if you know what you are doing and make it a practice to use a anti-oxidant for every electrical connection. For $5 you can buy a can of the best anti-oxidant ever made and will last you a life time of trouble free connections especially around the battery itself called SanChem NO-OX-ID A Special. Utilities, Water Departments, Telecom use it for all electrical connections. When you find the hard point use Dragon Tooth Lock washers to make the electrical connection. Use a very light coat of No-Ox on the wire skinner and contact area,

    Positive battery connection and routing vary a bit but real easy to figure out. Start by looking at the battery Term Post. Many manufactures provide an empty fuse terminal as part of the Battery Term Post connector assemble. May or may not already have a fuse installed. If it does have a fuse will likely be to high of a rating for your radio wire. If a spare terminal is not part of the Battery Term Post Connector, follow the heavy gauge wire to the Battery Fuse Distribution Block. There you should find an Empty Terminal for you to use. If they provide a fuse like I said is likely too large and you have two options. Replace the fuse and cut off the in-line fuse provided with the radio. Or leave the auto manufacture fuse in and connect your radio wire with the in-line fuse provided. Again use NO-OX on wire skinner and contact area.

    Routing is pretty straight forward on the drivers side wire channel underneath the plastic rails cover rails along the bottom of the doors on the floor board. Just pop them off. To penetrate the firewall there should be a empty grommet that you remove and replace. Be sure to put a drip loop where it passes through the firewall. Rout and secure the battery cable if zip ties along to battery either down the driver side if battery is on driver side, or up and over along firewall if battery is on passenger side.
    AI7PM likes this.
  4. N4MU

    N4MU Ham Member QRZ Page

    To summarize:
    1. Connect NEG radio lead to nearest chassis bonding point (probably in cabin area; not in engine area).
    2. Connect POS radio lead to battery terminal or, better, to "spare" fuse point on main fuse box if adequate amperage.

    I have a spare fuse location that is rated at 40A in the main box. I will look into using that if I can find where the load side wiring is stubbed or how to attach to the load side fuse contact, etc. As far as the negative return...I'm guessing there will be one available under dash area on driver side. More investigation needed.
    Since I have a diesel it has two batteries; one on each side of the vehicle. Any concerns with that? That is, since they are in parallel if I must use the positive terminal (not the fuse box) does it matter which one I use? I presently am attached to the driver side's a much shorter run as you would expect. Thanks for info.
  5. KF5LJW

    KF5LJW Ham Member QRZ Page

    Is it a Dodge Ram or a Fricking Ole Rebuilt Dodge? I had a 2011 and now looking at a 2016 Dodge diesel with dual batteries, and the battery setup is identical. It does not make any difference which battery you use. On the 2011 model I had on the Driver's side battery, the Positive Battery Term Post Connector has a Spare unused terminal. I used a Marine Battery Block Fuse (MRBF) on the Spare Terminal, and ran a # 4 AWG from the battery to a 200 amp rated Relay installed on the Firewall next to the hydraulic brake cylinder 1 foot away so as to operate with the Accessory. From the load side of the relay was wired to a Battery Distribution Block for the radio and various test equipment. You will not likely need all that but what I am driving at is the MRBF is a great way to get power from a battery. It eliminates any chance of accidental shorts and makes a great connection point. You can get them directly from Blue Sea Systems or most RV/Marine shops. I use a lot of them on solar applications to connect to batteries. They come in Single and Dual. Or you can use an inline fuses.

    So if you have a Dodge, look at the Battery Terminals, bet they have a unused terminal. Only issue using it is the radio will it always have power and will not switch on/off with key thus why I used a relay.


  6. N4MU

    N4MU Ham Member QRZ Page

    LJW: Thanks for info. Yes, I have a Fix Or Repair Daily. I am going to stop by the local dealer tomorrow and see if they have any "electronic gadgets" experts and ask a couple questions. I've had the radio in this truck for 2 or 3 years now without incident but now that I'm edumacating myself I am finding more and more things that I shouldn't do. I'm waiting to hear that I should not be using a red wire because of the dye in the jacket! Thanks again. Let's see if Ford knows anything...AND can give me any hint as to where the batter(ies) ground leads disappear to. It goes down there somewhere...damned if I can see where.
  7. KF5LJW

    KF5LJW Ham Member QRZ Page

    Another good place to ask questions, well 2 places, would be custom high end car audio shop and 2-way radio shops. If I were you I would tap the breaks before you do anything. If you have been operating without issues tells me if it aint broke don't fix it. One quick thing you can do if your radio has a built-in battery voltage display, is select AM or FM mode, turn TX power all the way up, and key the mic up and observe battery voltage. If it drops more than .4 volts, would indicate some power cable issues. Ideally you want to limit voltage loss to 3% or less. and if at RX you observe 13.2 volts with engine idling, anything below 12.8 volts in TX might be worth looking into.

    Check this out:

    Last edited: Jun 25, 2019
  8. N4MU

    N4MU Ham Member QRZ Page

    Any chance of having you send me a copy...pdf or whatever, that would be more readable? Looks VERY interesting buy I cannot read many items. Thanks, Bill ( papiflaps at gmail dot com )
  9. KF5LJW

    KF5LJW Ham Member QRZ Page

    Bill here is the link. What you want to pay attention to is the top center where the batteries are located. Negative terminals go to either the chassis/frame or engine block. Once you go to the link, just use Zoom
  10. N4MU

    N4MU Ham Member QRZ Page

    LJW: Thank you. I will download and look it over. I was able to discern what is probably known as the load sensor on the right hand battery. This is the way my vehicle seems to be wired...nothing on left battery neg terminal...sensor on left.
    UPDATE: (I can't wait to see feedback on this) - Just returned from local Ford dealer and while sitting in service manager's office with him and his top technical guy I was told that no harm would occur if the radio was connected directly to the pos and neg battery terminals. I made it clear about 20 amps on transmit and they came up with nothing that would cause harm to the vehicle and/or any sensors or safety gadgets, etc. What they did say was that if using the radio with the engine off for more than five minutes the vehicle would shut down. That function being part of the 5/15 minute shut down feature...really nothing to do with the transceiver. The shut down would occur if the (I presume) load sensor detected an abnormal load on the batteries. That all made sense and I know the vehicle will do just that. Since I've had the radio in the vehicle for years without any hic-cups (or worse) I guess I'll stay on the terminals. I will however resize the zip wire to #10 replacing the #12 I have now providing a bit more "headroom" for I-R drop, etc. - Especially if I go ahead with the FT-891 plan with the dual bander already in there. I have not performed the voltage drop check yet but will do so tomorrow morning (when it's not a sauna outside)
    Anyway, thanks for the link...a good piece of material to have! Okay...I'm done...go ahead all...

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