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griffin3

Dim TOAD lights through diode harness

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I am pulling a 2007 Chevy Avalanche behind my 1994 Bluebird Wanderlodge.
I am using the Roadmaster kit made for the Chevy Avalanche that has diodes and connects to the tail lights through the harness connections.

The problem that I am having is that the tail lights through the harness are very dim, no where near as bright as the lights when the truck is providing the power to the lights.

  • I tested the 7 pin to 6 pin tow cable and it tests good with little resistance.
  • I checked the voltage at the 6 pin end and I am getting 12 volts on each of the signal wires for the tail lights, turn signals, and brake lights. 
  • My RV does not have a tail light converter.
  • I converter the tail lights on the RV to LED.

Is there a way to check that the diodes are not eating up to much power? 
Should I be running a tail light converter to push more power to the TOAD?

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You will lose about 1/2 volt through a diode.  Its not comparable to judge the brightness from the truck when its running to when you are powering the lights from the motorhome.  You have 13.5 to 14.3 volts from the truck vs the same voltage from the motorhome but the 35 to 45 feet of number 16 or 18 gauge wire drops the voltage.

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Have you confirmed a good ground connection? Not sure if you have a separate ground wire in the harness or not. I had a trailer once which used the ball hitch to make the  ground connection, and it created a problem like you're describing. If you do have a separate ground wire in the harness, verify that the connection to the chassis is clean and tight on both the coach and the toad.

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Measure the voltage with everything connected if you can.   Perhaps across the bulb(s) themselves.  

Measuring 12 volts (or 13 or ??) at the connector without the lights connected is meaningless.  A high resistance connection (or ground) will still pass the full voltage when no current is being drawn. 

I like to use a 12 volt trouble light to probe the wires https://www.amazon.com/Voltage-Continuity-Current-Tester-Indicator/dp/B01BGZ9XRS/ref=sr_1_5?keywords=12+volt+trouble+light&qid=1572750908&sr=8-5  Try it across the battery first to get an idea of how bright it should be.  If there is a bad connection somewhere the light will be dim.

If you use one of these be sure to connect the ground clip to the ground lead in the plug to verify it is tied to a good ground.

Lenp

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griffn3,

Welcome to the Forum.

A quick way to check the ground to see if you have good contact would be to hook up as you always do. Then take your jumper cable and connect the chassis of the coach to the chassis of the toad. If your lights are better then  check the ground on the coach.

Herman 

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Change the tail & stop lights on your toad to LED. Leds are not as voltage sensitive as incandescent bulbs. 

 

Richard

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On 11/2/2019 at 5:02 PM, griffin3 said:

Is there a way to check that the diodes are not eating up to much power? 
 

YES.  Check voltage from the IN side of the diodes to toad chassis ground.  Then check the OUT side (going to the toad lights) to ground.

With no RV diode-based converter you should see close to RV chassis battery voltage on the IN side of the diode, so likely in the mid to high 13's. 

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Griffin3,. Welcome to the FMCA Forum !

The problem that I am having is that the tail lights through the harness are very dim, no where near as bright as the lights when the truck is providing the power to the lights.

Direction of current flow through the diodes to the load. 

       Output to load is the Cathode_ banded end  ----{<---  The input voltage goes the anode. 

Installing them in the wrong orientation will make for dim lights.  The wrong orientation can cause a number of issues depending on what type / or the circuit function. 

 Power in at this end     Related imageLoad end. Lights, fan or relays.

Rich.

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While I am not a fan of adding another bulb for each of the functions, our local RV dealer, Roadmaster and Chevrolet dealer state that wiring into the original lighting should not be done. Therefore, I added Roadmaster’s LED lights and their module to provide full voltage to them. All are equally bright. The module mounted in the rear takes the signal from the towing vehicle and uses power from a #12 wire that connects directly to the towed’s battery to operate the LED lights. No drop in voltage. I do have a charge line from RV to towed to maintain the towed’s battery. 

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A diode is reliant on its forward threshold voltage. If the voltage does not reach that the minimum voltage of the diode that is required,  it will not function properly.  Battery voltage level down can affect the output. There could be something causing a voltage drop at the anode and that would cause dim lights. Start checking voltage, first without the diode(s) inline and then with the diode(s) inline to see if there is a voltage drop at the anode. I'd even go so far as to install one diode at a time and check voltage.

The diode is nothing more that a one way switch. It keeps the voltage from feeding back into the system.

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The Forward Threshold Voltage is the amount of voltage needed to get the PN junction to conduct and allow current to flow in the forward direction. It's around 0.3V for Germanium and 0.6V for Silicon. If the voltage reached those thresholds, the lights would be beyond dim. They would be out.

 

Richard

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