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Old 09-23-2015, 06:17 PM   #11 (permalink)
padredw
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Yes, Rod, I did see that bulletin. I have copied it and will call it to the attention of my local Chrevolet dealer if and when I take it in. (Looking more like WHEN all the time!)

heymccall, would there be any significance at all that there is NO indication of electrical current when the brakes are applied--using a multimeter, of course. The other feamale posts for the lights all show appropriate current when activated, but there is zero display when the brakes are applied.

And, yes, you are correct in that the dashes do not change--have not changed since that first sign of trouble.

To give just a bit more detail: we were on a trip--almost home, everything working normally for almost 3000 miles. I stopped for fuel in Arkadelphia, AR and as we pulled onto the freeway ramp, the "CHECK TRAILER WIRING" came on and I tested the trailer brakes by applyng truck brakes and by manually engaging the controller. I had no trailer brakes. There was no effect upon the operation of the truck or of the brakes on the truck. I had no trouble, just driving carefully and allowing for the truck brakes to be used.

And that is where I am right now.

I just want to be clear about this: the fact that the multimeter shows NO electrical impulse when connected between the brake position on the plug (both inbed and bumper level) and the ground, when brakes are applied or controller manually engaged is relevant or not??? Does it, or does it not indicate that the problem is with the truck and not with the trailer?

I appreciate everyone who is trying to help. -- and I'm willing to listen and to learn.

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Old 09-23-2015, 09:16 PM   #12 (permalink)
heymccall
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The itbc sends NO voltage until the circuit is complete. Use a car headlight and piggyback your voltmeter. Or, just watch the headlight go bright and dim. A testlight probe doesn't present enough resistance.

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Old 09-24-2015, 07:54 AM   #13 (permalink)
padredw
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OK, mccall, I'll try to scrounge up some parts and give that headlight process a try. If I succeed, I'll report back here and see where to go from there.
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Old 09-24-2015, 03:10 PM   #14 (permalink)
padredw
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OK, here is the best I have been able to do so far. Let me know if this has any significance.

I used a trailer lamp from a utility trailer.Alligator clip to ground and to brake position on the seven way plug. No response of any kind. Tested with alligator clip to ground and to running lights--full illumination, also to turn signal post--proper intermittent flashing.

Does this indicate anything? Do I need different testing components? Still trying.
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Old 09-24-2015, 05:35 PM   #15 (permalink)
heymccall
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A low beam (or high beam) headlamp must be used, or two brake magnets. The system must see a circuit with a resistance of 2.5-1.2 ohms in order to recognize the brake circuit as complete.

You say you have a multimeter. Measure between the blue and white on your trailer. Is it between 2.5 & 1.2 ohm?

Does the truck 3td brake light work?

Again, based on all you've posted, the pressure switch in the master cylinder is suspect, as most other issues won't even give you dashed lines for trailer output.
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Old 09-24-2015, 08:20 PM   #16 (permalink)
padredw
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Yes, I was afraid of that. I got a reading of 1.4 ohms between the ground and brake posts on the trailer umbilical, but then the multimeter failed. Looks like a fuse, and of course I don't have one.

As you noted, the dashes are "static" and there is no longer any error message. The gain setting can still be set and that readout appears, but no "output" bars, just the dashes.

Looks more like I will have to take in to the dealer. I really believe the problem is in the truck control system, but am not absolutely sure of that.

If I could find a sealed beam headlamp, what would that test tell me?

And thanks for all the help.
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Old 09-24-2015, 08:32 PM   #17 (permalink)
heymccall
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The headlamp was to rule out the integrity of the trailer wiring.
Again, I believe the pressure switch is bad. Unthread the old one and thread in a new one. Then, bleed the front calipers.
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Old 09-24-2015, 08:50 PM   #18 (permalink)
padredw
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Thank, I'll give that a try. Will report back in a few days.
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Old 09-25-2015, 10:23 AM   #19 (permalink)
Ron Nielson
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If there isn't proper resistance in the circuit, will the DIC display the dashed lines? Just checked my truck, no trailer connected, no dashed lines on DIC when brakes applied. I think this argues for making the headlight tester.
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Old 09-25-2015, 01:32 PM   #20 (permalink)
padredw
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Just now have a chance to respond to last post.

The display on my DIC is what I would call "static." The gain setting and the dashed lines are displayed either by pressing the manual controller or by browing through the information button on the steering wheel. It will remain displayed until another button choice is made. The display seems to have nothing to do with the brake pedal being depressed.

I am not very good at the terminology, so please allow for that.

I am not sure I have the experience required to change out the pressure switch and to bleed the lines as required. So maybe I should turn to the local dealer. Even if I do so, this has been very valuable for me to know more about the ITBC and the problems I and others seem to be having.

Thanks for all the help, and I am still listening and willing to learn.

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