Loosing taillight voltage with trailer?

[Bryan]

Hey guys, we are trying to wire up for attaching a trailer. When we hook it up, all the taillights on the bus get dim. Also the trailer lights are dim. Any suggestions? Thanks!

[Bryan]

and to clarify, the front marker lights are not affected, only the rear end of the bus (taillights and markers)

[Ace]

What kind of bus? Led's on either! More info!


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[luvrbus]

It's a ground problem fwiw

[Bryan]

What kind of bus? Led's on either! More info!


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GM 4107, there are no LEDs, but would that help?

[Bryan]

It's a ground problem fwiw

would the ground problem be on the bus or the trailer? As you probably know, underneath the engine hood directly behind each taillight housing there is 5 screw in connections for wires.

screw#1. Ground
screw#2. Reverse (which don't work) [any suggestions?]
screw#3. Blinker
screw#4. Brake Light
screw#5. Markers

We have connected the trailer ground wire to the bus ground connection screw #1. If the ground issue is within the bus, would it be smart to run another wire from screw#1 to a metal part of the bus? or does that even come close to fixing the possible problem? Of course when I look at ALL the wiring in the engine compartment, it's quite intimidating  LOL!

Thanks for your help

[Seangie]

Bryan - if its not a ground problem it could be that the locaton the lights for the trailer are tied in is on the other side of the bus tail lights wiring the trailer lights in series with the bus lights as opposed to being wired in parallel.  That would cause a voltage drop across the lights.


-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Don4107]

When I picked up our 4107 and turned the lights on as it got dark my chase car said tail lights are flashing on and off.  Was only grounding through the hinge.  A pair of vise grips to hold the broken ground wire to the frame got me home.

Don 4107 now MCI5B

[luvrbus]

GM got real creative with the wiring on some of the 4107 and 4108 buses ,I fought grounding on 1 for a week till a GM guy told me some operators ordered those buses with the grounding done through relays a piss poor idea IMO  don't you know the one I was working on was ordered that way

[robertglines1]

If a big if here! any type of 3 to 4 wire box converter is used. Lots of problems are traced back to them being unable to handle the amperage needed of many lights. I think that prompted the led question.  Ground is of course the first choice..  Bob

[Bryan]

One thing I failed to mention is that we don't actually have the trailer hitch attached, just the wires which has a ground in it. I know that sometimes the hitch makes the ground but I figured the ground wire would be enough

[Bryan]

Bryan - if its not a ground problem it could be that the locaton the lights for the trailer are tied in is on the other side of the bus tail lights wiring the trailer lights in series with the bus lights as opposed to being wired in parallel.  That would cause a voltage drop across the lights.


-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

Thanks Sean. I'm using the right side of the bus for all the connections with the exception to the left blinker, are you saying that we need to use the left side with the exception of the right blinker? Thanks!

[Oonrahnjay]

...   I know that sometimes the hitch makes the ground,,, 

      Yeah, some people do that but it's about as bad an idea as you can come up with.  You *really* do want a good, low-resistance wired ground from and through your trailer harness to a solid ground on your frame (or other appropriate ground point). 

      The ground thing just screams out at me, too, but what Sean said about wiring in series is something to think about -- that's exactly how the lights would work (it would drop the voltage in half on both of them) if that was the problem.  It would be possible to have a good ground to one light and have it bright and a bad ground to another and have it dim (of course, a combined bad ground would dim them both) -- the fact that both lights go dim when they're together and at least one is bright when they're not wired together puzzles me.

      Of course, the biggest principle when dealing with electrical stuff is "NEVER assume that you have only one problem"!  In this case, I'd check bulbs and sockets for corrosion, the grounds (and I'd check to see if the resistance/ohmmeter reading is the same from all the bulbs), and the "hot side" wiring -- and everything else I could think of.  If you have more than one problem and you only fix one, there's a good chance that the one(s) you didn't fix will show up on the side of the road late at night in a cold rainstorm.

[Bryan]

okay, thank you everyone for helping me with this. Here is a new update. Just incase it was the fact that I didn't have the hitch attached, I hooked jumped cables from the hitch to the bus frame. This made NO difference. Wiring in series and parallel was a little confusing to me, so what I did was detached the wiring harness all together, leave the jumper cables on, and ONLY attach the marker lights (screw#5, as stated in earlier post) wire to the trailer. Although the trailer markers lit up, they are still dim, and it also dimmed the bus lights as well. Here is a short video to show the amount of dimming when connecting to trailer... www.youtube.com/embed/PLwuUhMdhxM

[Bryan]

I've continued to research this, and I found a suggestion that since I have a lot of running lights on my trailer (about 20), that it could be sucking all of the voltage out, if that is the case, I found this product to upgrade the voltage, basically you hook it to your battery and to your tail light wiring, then connect it to the wiring harness... http://www.etrailer.com/Custom-Fit-Vehicle-Wiring/Tow-Ready/119179KIT.html

here is my question, I'm concerned that being that the bus is so old, could this potentially create bigger issues? or is the worse case senario I blow a fuse and have to replace it? I certainly don't want to short out my tail light system entirely. 

Thanks for your input guys! What would I do without you BusNuts?