Quirky Trailer Port voltages

[mrlewp87]

[size="5"][size="4"]The Ridgeline RTL already had the 7-pin port for trailer lights. I needed to convert the wiring to the flat 4-pin type. Purchased a decent plug that allows you to custom wire the hook-up.
Before doing the final steps of sealing things up for eventual use, I used wire nuts to join the leads from vehicle port to a 4-pin trailer plug. Using a digital MM I of course checked for continuity from the new 7-pin plug to the flat 4-pin. All appeared fine, achieving all 0.00 readings for each connection.. AND confirming the correct 4 terminals between plugs.
In testing the vehicle's 7-pin port, I found readings for ground, tail lights, and emergency lights (subbing for brakes) were all good to go. Strangely though, turning on either the Left or Right signal indicated voltage at each signal terminal? However, depite this quirk, all lights functioned correctly on the vehicle. Is it possible that full voltage was correctly present for L and R, and maybe a lesser and insignificant voltage was present at the opposite terminal? Difficult to know because of how the readings swing wildly if measuring a pulsing DC voltage.
Yes, I did check my adapter's Ground connection, and the vehicle's Ground pin. Both were fine! So, what's up here?? Any guesses?
(PS; I moved this post from the Honda Ridgeline forum, with heavy editiing done. Hope I made it clearer than the origiinal)

[shorod]

So are you splicing into the wiring for the 7-pin trailer jack with a 4-pin connector with pigtail wires? If you disconnect the 4-pin splices, do you still measure voltage on both turn signal wires of the 7 pin jack? Do you have a old style test light that you can use instead of the digital multimeter? I'm assuming there was no trailer connected at the time you did the tests with the meter, correct?

-Rod

[mrlewp87]

(i wasn't sure what my thread would look like after some major edits on the original. Then doing a copy/ paste as a new thread, different forum. It was all very 'glitchy' and weird behavior. I finally gave up, wondering why I couldn't just MOVE my original post from one forum to the other?)
To your questions; I think it could be assumed that I was testing the 7 pin port terminals, without anything else connected.(the trailer) I then noted that the truck lights were operationg normally, despit the odd readings at the trailer port.
Here's where some 'glitching' may have occurred in trying to copy and paste my original post AND new information that followed when replying to myself. If anyone had wondered, I did test out all lights on the trailer using a separate 12V source. They all worked fine.
Then, despite the odd readings on the truck's 7 pin port, I went ahead and connected the trailer using my 7 to 4 pin adapter (<thoroughly tested, and good) Even more confusing; truck lights still working fine, I know the trailer lights and wiring are all good .. but NO trailer lights are responding at all now that it's connected to the truck!? I thought that at least the running lights and perhaps the brake lights would work, with the L and R signals flashing together per the odd voltages found at the truck port. But nothing at all!, was a stumper.
And for my final Reply to Myself, plus "problem solved" message. Since all behind the truck had been tested, I delved into the fuse question. (btw, this vehicle is new to me. I hadn't even lifted the hood yet!) Finally located all fuses having to do with trailer lights. Pulled each and eyeballed them, then used the DMM on Ohms. Sure enough one 7.5A fuse was blown. That one little fuse, identified as trailer hazard or such, caused all this chaos with the entire light system. Now all lights are a GO!
I could've led with this, right? I have my reasons but choose to not say. I should know from past experience that choosing the obvious, relative forum heading doesn't always get you the results you hoped for.

[shorod]

I'm glad to hear you have it working now.

For future, this is a pretty good example of why you may want to sometimes reach for the old fashioned test light when a digital multimeter (high input impedance) is providing readings that don't make sense with some of the other observations (such as reading voltage but not having light). The test light will provide a load on the circuit which a DMM will not. When working with circuits involving incandescent light bulbs especially, a DMM may read what looks like battery voltage through the bulb even when the current capability is too low to light a bulb. I'm not positive that's what happened here, but since you had an open fuse, it seems plausible.

-Rod

[mrlewp87]

Thanks, shorod. I get what you're saying there. I've moved on to other pressing matters, and got behind in my emails. It never occurred to me that there might be separate fuses for the truck lights and trailer lights. With there being 2 fuse boxes inside under the dash, and 2 fuse boxes under the hood it took a while to narrow the hunt down for a possible blown fuse.