Turn signal "flasher" units

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Dean Huster
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Turn signal "flasher" units

Post by Dean Huster » Thu Jul 13, 2006 8:47 am

I pull a 5th-wheel travel trailer. It's getting to be around 18 years old and is showing wear. We bought a new Dodge 1500 in 2001 to pull it, as the old 1979 F-250 had all systems failing. I installed the hitch, brake and all other electricals (I always use bare crimps, then solder, then add lots and lots of heat shrink) and all was well for a bit.

Lately, I've been having a lot of trouble with the exterior lights being intermittent or dim. Finally got the interconnecting cable solid and still had dim lights. I got to checking underneath the truck and found that the truck is not feeding full battery voltage to the lights. I wonder if there's any built-in voltage drops through electronic switching that might cause this. If not, I'm going to have to do a major wire search with the voltmeter to find the drop. I'd like to head that one off for as long a possible. When I tried the ol' wire trace to find a short in the brake/turn signal systme in the F-250, I ended up somewhere in the steering column. That's why we got the new truck.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

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bearing01
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Post by bearing01 » Thu Jul 13, 2006 9:49 am

Are we talking about park lights here or signal lights? Or both?

Most of the time the problem with park lights is a bad ground. Especially on something like a boat trailer or maybe even a travel trailer. Alot of times the trailer isn't galvanized & under coated like your vehicle and the chassis rusts out alot sooner. This could give you a bad chassis ground.

First thing I would do is measure the voltage at the pins of the wiring harness going to the trailer's park lights, using the connector ground pin as your reference. If you don't have near battery there (12.6V) then it could be the vehicle. In that case go to one of your park lights, remove the bulb, and measure the voltage in the socket. If again you don't have battery voltage then it could be the truck's wiring itself. This will most likely lead you to a bad ground somewhere or to a bad (high resistance) light switch. Make sure you got 12.6V at the light switch when the park lights are on. With the lights on you should be getting no more than 0.1V less than battery voltage at the lights themselves. If you plug in a trailer and draw alot more current through your light switch, and use this trailer alot, then you can cause your light switch contacts to become pitted and corrode. This of course would be a result of alot of use over time with the trailer plugged in. It would also cause the truck's lights to become dim as well as the trailers.

Once you got the truck wiring figured out then move on to the trailer. With the trailer not plugged in, again measure the park light voltage at the connector with park lights on. You should be getting same voltage that's at the car's park lights. Now plug in the trailer and try to back-probe the trailer connector to see what the voltage is at the connector with the trailer drawing current. If the voltage has droped like 0.1V or so then you could have a poor connection where the truck side trailer plug taps into the truck's wiring. You could be pulling current through a bad connection that will cause your voltage to drop by 0.1V or more.

Once you got the connector all figured out, then move on to measuring the voltage at the trailer's light sockets themselves. If you got less volts at the light sockets then what you had back at the connector then you got a voltage drop in the trailer. This is most likely due to (a) corroded wire connectors at the lights themselves or (b) a corroded trailer ground. Alot of times a couple lights may be grounded together at one point. If that main ground point is rusted then that set of lights will be more dim than the others. If some of your lights are dimm while others are not then check that common ground point that's common to all the dim lights. If individual lights are dim then it's probably a corroded connection (ie ground) of that particular light. If all the lights are dim then either it's a common main ground that is bad... or the problem is back at the connector.
[quote="Chris Smith"]What does the smell of “piss in the windâ€

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Externet
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Post by Externet » Thu Jul 13, 2006 3:08 pm

Hi Dean.
Do your voltage measurements along the wiring with a ~21W light bulb in parallel to the voltmeter probes. :smile:
Miguel

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Post by bearing01 » Thu Jul 13, 2006 3:49 pm

Externet wrote:Hi Dean.
Do your voltage measurements along the wiring with a ~21W light bulb in parallel to the voltmeter probes. :smile:
Miguel
Miguel,
What is the purpose? Is it to draw current out of the node you're measuring the voltage at... to see if there's I*R drop?
[quote="Chris Smith"]What does the smell of “piss in the windâ€

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Externet
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Post by Externet » Thu Jul 13, 2006 9:27 pm

Hi.

Any dimming of lights has to be related to a resistance in the circuit. The problem is locate in which connector, splice, contact...

A plain voltmeter has too much resistance to draw enough current. The modern 10Mohm are even worse, very counterindicated for automotive use, as you can probe a wire that has no metallic contact with the supply but still indicating 12V passing trough a sulphated/corroded/wet gap.

G----------(-)B(+)--------------10M------------V-------------G

Being G='ground'; B=battery; V=voltmeter; 10M a ~ten megohm resistance from a broken but wet/corroded connector. Note the 10M can be at ANY place in the ----- circuit.

The voltmeter will still register 12V. But loading the circuit, will not supply any current.
If V has in parallel a decent current draw as a bulb, the voltmeter then will read the reality: 0V

Am not good at explaining some things, but can reword it if you want. :smile:

Miguel

Dean Huster
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Post by Dean Huster » Fri Jul 14, 2006 5:18 am

Valid replies, but wrong problem. It's not the trailer. Voltages on the truck are measured across the lamps, so obviously we have a load, so meter impedance isn't the problem (we're not checking an "AA" cell"). My general question here is simply this: do the electronic "flashers" (as an example) exhibit any appreciable voltage drop over their mechanical predesessors which had virtually none?

It's been over a year since I last put the meter to the problem. Once I found low voltage on the truck side of the cable, I new where the problem wasn't -- cable or trailer.

Note that on travel trailers with the typical 7-wire Bargman connectors, you never rely on the hitch for ground. The ground is part of the wiring, which it should be even on the rinky-dink connectors for boat and utility trailers.

If memory serves me correctly (I had major sub-zero temp open heart surgery on June 1, so my brain isn't hitting on all seven cylinders yet) I was measuring a 1.5 volt drop on tail or turn signals with 12 volts measured at the battery. It's just weird for a fairly new truck to do this.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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Bob Scott
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Post by Bob Scott » Fri Jul 14, 2006 1:03 pm

Dean,

I hope you recover from surgury quickly. I am soooo tempted to add my own nightmare experience last year in ICU with you in fine detail but it would be just too far off topic.

When you do quick troubleshooting you can take shortcuts to save time. It's when results are confusing that you have to change tactics and start troubleshooting from "square one", with no shortcuts. Try checking the voltages when you have a separate wire connected from the DVM directly to the battery negative terminal. I mean, you have to be able to trust your voltage REFERENCE first. THEN check both sides of the bulb for voltage so you can figure out whether your missing voltage is on the high side of the bulb or the low side.

Then check your local library if you don't already have a wiring diagram for your truck. That knowledge added to your capable brain should get a solution off and running.

Good luck and good health,
Bob

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Chris Smith
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Post by Chris Smith » Fri Jul 14, 2006 7:14 pm

Chris Smith wrote:What does the smell of ““piss in the windâ€

Dean Huster
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Post by Dean Huster » Mon Jul 17, 2006 7:09 am

Trouble is Chris, the down-side of relaying everything is that you add another possible failure point to the system. Besides that, it's a bit difficult to work something like that with the trailer brakes. The "K-I-S-S" principle has to be in effect for safety. That's why I never encourage folks to screw around with (i.e., make cut accessories for) the bulk of the safety electronics of their cars, e.g., headlights, turn signals, stop lights, etc. But, on the technological end of things, yes, it would be a lot of fun to do something like that.

Still, it doesn't get around the question of WHY with no trailer, am I getting lower voltage to the lamps. I'm just going to have to find a day AFTER ALL THE DANGED MOSQUITOS HAVE DIED to troubleshoot the thing.

Dean
Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

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Chris Smith
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Post by Chris Smith » Mon Jul 17, 2006 2:56 pm

Dean after enough failures, and for your self, you do it right.

What I have found over the years especially with trailers is KISS never works, much like the predicament your in now.

USE a relay, a TRIAC, or even a FET and power the box directly from a large wire from the battery.

Relay/switch everything with power, ground, and relays and just be done with it.

Last time I recall in the early 80s, they junked all the wiring in the car, placed a signal switch in every component, ran only three wires around the complete car, and when something was activated a signal was sent down the common wire like a X-10 system to tell the relay to happen, open, or close. Talk about making it simple?

Even the AC worked this way. And you don’t want to do a trailer?

I think your looking at the dinosaur in the wrong light, this is KISS.

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Post by myp71 » Sun Aug 27, 2006 9:33 pm

Dean,

Does your truck have a trailer brake contorller on it? Maybe its that giving out or going bad..?

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Post by Ed B. » Mon Aug 28, 2006 1:43 pm

Dean -
Bad Ground ! Bad Ground ! somewhere.
Ed B.

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