Klein multi-meter not giving results I expected in tracing wires.

[Yoda]

OK I took Jim's TucsonJim class at the National a year or so back. but now I am wondering if I actually passed? I am totally stumped.

Tracing the taillight wiring today. I found the red (left turn) and brown (right turn) wires along with the green clearance wire.. https://offroadofficial.com/wp-conte...6/7-pin-RV.png I actually started at the pin box and checked wire colors and then went through my various pictures and feel confident that GD did run the wire colors correctly to the rear. Fortunately there is enough slack to work with.

I put the meter to read voltage, grounded the negative to a bolt on the frame and used the positive to probe the butt connectors behind the taillights.. For the turn signal I was expecting 10-12 volt pulses as it Flashed. Nope was seeing 7 to 8olts varying but no zero reading between flashes. This was the same for both sides. Is there the a chance the meter did not like the flashing. As for clearance lights I got 9.5 volts when on and zero off. However then there was zero voltage on the right/left turn when blinker was off and just clearance on.

It got late and I was tried - will try again tomorrow. I think instead of the frame bolt as ground I will use the other probe in the white wires - maybe that was the issue?


PS For folks with older trailers check you taillight seals and bolts holding the light on. Both were loose and some screws striped. So plugged the holes with tooth picks and reinstalled once checking and calking was done. Screws showed a bit of rust - no other damage. I hope I caught it in time.

The upside is I found a good place to mount the plug on the trailer. Downside my back is killing me

Thanks for any thoughts.
Keith

[Scott'n'Wendy]

grounded the negative to a bolt on the frame
Keith

This is your problem. Use the common in the harness.

[TucsonJim]

Keith - That reminds me. It's time for your annual refresher training....

Jim

[Lonestar]

This is your problem. Use the common in the harness.

I have a 4 pin flat plug that was *factory installed* that I used for a LED light bar. I remember on the install taking a measurement with my Klein VOM and it showing a flakey voltage as measured directly off the tail light pins and the ground pin. Since the wiring harness for the pin disappears up into the underbelly, I don't know it the ground goes to the frame or if it actually goes to a common ground wire, but the voltage measurements seemed unusual to me.

Jerry

[Yoda]

I have a 4 pin flat plug that was *factory installed* that I used for a LED light bar. I remember on the install taking a measurement with my Klein VOM and it showing a flakey voltage as measured directly off the tail light pins and the ground pin. Since the wiring harness for the pin disappears up into the underbelly, I don't know it the ground goes to the frame or if it actually goes to a common ground wire, but the voltage measurements seemed unusual to me.

Jerry

Jerry
Thanks for the input - and here I thought I was loosing my mind. Jim TucsonJim I think I need a 12 or 13 step program than a refresher course . I will pull out the Klein manual though. I am also going to dig out my old RadioShack analog multi-meter and compare readings.

The white negative return wires are grounded at 3 points on my unit. A heavy frame ground below and behind the distribution panel (both 120V bare copper and a 10 gauge 12v white wire share a welded frame stud), a ground at the power block in the front bay and the last is at the kingpin, for the 7 pin connection. Scott's Scott'n'Wendy comment does ring a bell as all of the trailer functional lights - break clearance, turn, do have a home run for the negative returns to the kingpin. Its separate from the other 12v circuits. So tomorrow I'll wire the negative return into the taillight wiring harness and try again.

I did notice the flakey readings like you had Jerry too when I was poking the other connections to see what was hot or not.

Keith

[TucsonJim]

Yoda - For curiosity sake, you could also set your meter to ohms (Ω) and measure the resistance from the return ground wires to the bolt you tried to use for ground. Any resistance will cause an equivalent voltage drop.

Jim

Jim

[ncitro]

I know on my truck the output going to the lights is not clean. I have a set of lights I added that attempt to count the pulses to determine if its the turn signal vs the brake lights (same wire). It works fine on my friends GM, but does not work on my 2019 or 2024 Ford. I had one of the guys throw the oscilloscope on it at work and sure enough its not clean DC, its a modulated signal thats pretty noisy. Works fine for bulbs but anything more complicated (your digital meter included) has a hard time with it since it is not clean DC. An old fashioned trouble light would probably tell you what you need to know.

[Yoda]

Thanks everyone
I am off to the parts store to get the correct wire colors I need - trying to do it correctly so down the road I know what I have. Its amazing with all the wire scraps I have I don't have the correct colors in 16 gauge which is the gauge of the Hopkins Towing Solutions harnesses I am using. The trailer lights wiring looks smaller than the 14 gauge I am used to seeing, but Ill know when I do the splice.

Jim TucsonJim If I try what you suggest (negative return white to the frame bolt on ohms) I should see infinite resistance correct? But I could be not understanding.
Neil ncitro Maybe as I have the 2022 Ford that's why I was getting the floating voltages but not zero between flashes.

Learning as I go here.

Keith

[ncitro]

Between the frame and white wire you should see low resistance. Maybe a few tenths or hundreths of an ohm. Infinite would indicate the white wire and frame are not connected.

[Yoda]

Between the frame and white wire you should see low resistance. Maybe a few tenths or hundreths of an ohm. Infinite would indicate the white wire and frame are not connected.

DOH!!!!!!!!!!!!!!!!!!!!! I had it backwards

Thanks

[Scott'n'Wendy]

Thanks everyone
Jim TucsonJim If I try what you suggest (negative return white to the frame bolt on ohms) I should see infinite resistance correct? But I could be not understanding.

Keith

Yup...refresher required....

[Yoda]

Yesterday I got 90% of the splices done and sealed (heat shrink tubing). The last is my reverse wire which means I need to get above the coroplast in one corner. Ill be testing today before installing the 5 pin plug to be sure everything works - should be fun. This time testing will use a trailer white wire as negative return ground. Pictures to come.

Keith

[Yoda]

Update
Well the warm weather is gone for about a week (back to rain/snow, cold), so the project is delayed about a week..I still plan to do a number of suggested tests with the meter then. It does give me time to work on the harness to run along the hitch to the trailer inside and test the light.

Keith

[Yoda]

DOH! DOH! DOH! DOH!

It helps to have the meter on the Correct Scale

Was getting the same flaky readings on my new wiring, then I noticed the AC icon present. Switched to DC and everything is good.

Yep I do need that refresher course.

So have a good laugh on me

Keith

[TucsonJim]

Keith, Keith, Keith. Please send your diploma back. LOL