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Old 03-10-2016, 10:26 PM   #1
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Diodes in the tow car

I am just setting up a geo tracker as a tow car for my 1999 safari contenital 4006 40 footer. It is my understanding that diodes are required to protect the m/h electrical system. Is this necessary? I plan to place just one diode on the brake light line as this is only line that could feedback power ( i have a brake buddy in the tow car) all this said I thought prehaps I could simply pull the brake light fuse in the tow car in place of a diode .? any thoughts
would be appreciated. Thanks all

Wayne
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Old 03-10-2016, 10:33 PM   #2
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I have wired a couple vehicles for towing. I used the RoadMaster diodes in both and never had any problems. But I did follow their instructions as the Ody has quit a bit of electronics in it, plus it was still under warranty. Even so the Honda dealer tried to blame the wiring for a bad antenna wire even after I showed them a magazine article about the bad antenna wire.
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Old 03-10-2016, 11:04 PM   #3
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Waynepacy,
Well Sir, there's a couple of schools of thought on this matter. We've towed 8 different Jeeps, one Toyota pickup, one Honda CRV and one full sized GMC Sierra 1500 extended cab 4x4. Each and every one of them were all wired the exact same which, utilized the stock tail light bulbs for toad lights. And, in all of those vehicles, I've installed only two diodes, one for each side of the brake/turn wire.

And, I have NEVER, EVER wired in a diode to "protect" the coach wiring, in 35 years of towing. There are some that think it's absolutely necessary. Well, if they want it then, be my guest and wire them in. The primary reason for wiring a diode into the toad side is, to protect the M/H wiring.

Well, I suspect that in our life time, towing all of those different toads, that we have "back fed" the coach, oh, maybe a hundred times or so and, not one of our coaches EVER went up in flames due to no diode for feed back protection to the coaches light/wiring.

I do however, install a diode, one in each turn signal/brake light wire, IN THE TOAD wiring to prevent the signal from traveling up stream to the toads steering column which, would confuse the entire lighting system and nothing would work correctly.

And, I've not ever purchased the expensive diodes sold in Camping World or, any other RV parts supplier. I simply purchase mine at Radio Shack for about, $3.50 for a four-pack of the largest diodes they have. I solder them in and, DONE!

Now, this is how I do it and, like previously stated, not one problem, ever, in any of the toads wiring or, not one time was any of the coach wiring in jeopardy. The wife handles the toad prep side for connecting and disconnecting while I handle the tow bar/cables/pig tail/ auxiliary brake attaching.

And, occasionally, she beats me to the point where I'm disconnecting things after we've arrived at our campsite and, fires up the Jeep or, what ever we're towing at the time. Well, when she does that, the lights (usually daytime runners or, even marker lights) will light up on the Jeep. If I've not disconnected the pigtail before she fires up the Jeep, then that signal travels through the pigtail and, lights up the coach lights, BIG DEAL!!!!!!!!!!

Four coaches and 35 years and, not one has ever had any electrical damage due to an action like that.

But, if you, or anyone feels the need to prevent that, then install a diode so that can't happen. Good luck.
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Old 03-11-2016, 01:39 AM   #4
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in line radio shack diodes

Thank you so much for your overview. I agree the radio shack diode should be as good as any with respect to backfeeding the m/h,

This was and is my only real concern as i towed the tracked down south this seaon with no diodes. My only concern was that the tow vehcile lights were dim. I have to travel with the ignition on to unlock the steering and now i am about to start using a brake buddy with a break away kit. With the brake buddy the tow car brakes will start to be used by the brake buddy when i am hard braking and i am concerned that the same line will carry the signal to the lights from the m/h. So the diodes should protect the m/h.

thanks again for your input

wayne
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Old 03-11-2016, 08:21 AM   #5
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Wayne
I have a 7 pin connector on the coach to a 6 pin connector for my Blue Ox tow equipment. I believe the center pin of the 7 pin cpach connector carries 12v DC from the coach. I connected it to a spare connector on the 6 pin vehicle connector and wired a 12ga circuit to the battery post in the vehicle. This keeps the battery topped up and in your case, is likely mandatory with the ignition on. Be sure to wire a 10+ amp automatic reset breaker in the line to the battery and you should have bright lights again.
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Old 03-11-2016, 08:36 AM   #6
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My understanding is with newer toads and motorhome the diodes are suggested to protect both of them. As you put on the turn signal in the motorhome, the current goes back to the toad and without diodes it can travel back into the toad's system. If there is any electronic systems connected they could be effected. Same way for the tail lights. As you turn them on, electricity flows to the toad tail light bulb, and without a diode it can flow back into the toads system. Also if you hop into the toad and put on the tail lights, without a diode current could flow back into the coach. Same for the Brake Buddy. As it applies the brakes in the toad, current flows to the brake lights. These same brake light filaments can be used for turn signals. If so, than without diodes the current will flow back to the motorhome.

In the old days when everything was simply switched connections, it didn't matter all that much, but with computers controlling just about every aspect of a vehicle, reverse current can matter. (notice my choice of words "could" and "can". Each vehicle is different and some of them may be effected and some may not depending on the electrical safeguards the designers put into the electrical scheme).



As for dim lighting in the toad, check the voltage at the plug when the toad is connected and a light is activated. I'll bet you find a low voltage there. Problem is the current has to flow a long ways before it lights the toad lights.

I see two possible fixes: There could be a comprised ground connection between the toad and motorhome. I would first run a temporary ground wire between the toad chassis and the motorhome chassis and see if that helps. If not, then an alternative solution is to install relays to take motorhome battery current and through a relay activated by a taillight signal send it to the toad. My mature Freightliner coach had that same problem of dim toad lighting. My newer Freightliner chassis has the relays and the toad lighting is fine.

Here is a wiring schematic I came up with for my 97 coach. I spent $23 buying the relays, wire, bracket and fuse holders back in 2004+-. This turned dim toad lighting brightness into normal toad lighting brightness. It looks very much like the Freightliner designed module in my 2006 coach.

One last comment/suggestion, add a charge wire to keep your toad batteries charged. With the Brake Buddy, it is using toad battery for the brake lights and as the toad battery looses charge it will dim the stop lights.
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Old 03-11-2016, 08:47 AM   #7
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No diode in my Jeep Wrangler setup. I purchased a wiring harness from CooltechLLC, which has a plug that interfaces the rear driver's side tail light of the Jeep. You plug their harness inbetween the tail light and the Jeep wiring that normally connects to the tail light. Then all I had to do was route the cable to the front of the Jeep and wire in a connector. No diodes... no problems. I can't actually conceptualize where any problems would come from anyway? I'm not connecting to the Jeep battery in any way whatsoever. To get Jeep power to the Jeep lights from the Jeep battery would require that the Jeep be turned on, and the Jeep turn signal be actuated. This simply isn't going to happen when the Jeep driver is in the RV driver's seat. (Remember... turn signals don't work when the ignition isn't on, which means that the electrical circuit is not closed. Without a closed electrical circuit, electricity cannot flow--forwards or backwards.)

Now... maybe other wiring harnesses are different... but I can only speak to my own.
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Old 03-11-2016, 09:17 AM   #8
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Quote:
Originally Posted by Bigd9 View Post
My understanding is with newer toads and motorhome the diodes are suggested to protect both of them. As you put on the turn signal in the motorhome, the current goes back to the toad and without diodes it can travel back into the toad's system. If there is any electronic systems connected they could be effected. Same way for the tail lights. As you turn them on, electricity flows to the toad tail light bulb, and without a diode it can flow back into the toads system. Also if you hop into the toad and put on the tail lights, without a diode current could flow back into the coach. Same for the Brake Buddy. As it applies the brakes in the toad, current flows to the brake lights. These same brake light filaments can be used for turn signals. If so, than without diodes the current will flow back to the motorhome.



In the old days when everything was simply switched connections, it didn't matter all that much, but with computers controlling just about every aspect of a vehicle, reverse current can matter. (notice my choice of words "could" and "can". Each vehicle is different and some of them may be effected and some may not depending on the electrical safeguards the designers put into the electrical scheme).

Agreed. Every manufacturer designs their own circuitry and may or may not design in provisions for future user-added connections. The value of the diodes is to change all the "could" and "might" possibilities to "can't" and "won't". It also offers some protection against claims that unrelated electrical failures in the car were caused by your upgrade (i.e. warranty issues).

As an FYI: The Brake Buddy in my GM toad does not operate the brake lights. The current comes from the motorhome. When the ignition fuse is pulled for towing (as recommended in the GM owner's manual), the brake pedal switch no longer operates the brake lights. The BB does use some toad battery current to run its internal compressor and circuitry, which is why I installed a small battery charger connected to the center +12V pin on the 6-pin connector.
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