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Old 11-28-2022, 01:13 PM   #1
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One Dead Brake Light

Brake lights worked before travel. After 70-mile trip, next light test revealed driver's side brake light inop. I pulled the light assembly off (oops, it got ugly) and swapped the brake lamp with the turn signal lamp below it (same PN). Lamp was good (worked when moved), and problem remained with the brake only.

There is just 1 20A fuse in the Rear Fuse Panel, and there is also 1 15A fuse in the Front Panel. Also 1 BRK RLY.

There are 2 BRK SIG Relays in the Front Fuse Panel, but unclear if they feed left/right. Also 1 BRK RLY.

Given one brake light is fine, any thoughts on a troubleshooting approach? I do have a multimeter.

Thanks in advance,

Paul
2011 Holiday Rambler Ambassador 36PFT
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Old 11-28-2022, 01:32 PM   #2
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Follow the ground from that light , it may be rusted or loose.

Second brake light relay may be for trailer lights.
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Old 11-28-2022, 01:50 PM   #3
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Quote:
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Follow the ground from that light , it may be rusted or loose.

Second brake light relay may be for trailer lights.
Will check ground. [In case it matters at all, the tow vehicle brakes all work fine when connected]

Paul
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Old 11-29-2022, 06:12 AM   #4
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Swap the two relays you found to see if problem follows one of the relays.

Use a 12 volt test light at the bulb to see if there is sufficient voltage/current to make it light up. If the test light does come on, put your test light onto the ground side of the light. If it comes on but dimly the ground side is defective.
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Old 11-29-2022, 04:28 PM   #5
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Aren't there two pressure switches on the exterior firewall opposite the trendle pedal? Switch the wires.
See is the problem switches sides.
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Old 11-29-2022, 05:11 PM   #6
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Aren't there two pressure switches on the exterior firewall opposite the trendle pedal? Switch the wires.
See is the problem switches sides.
Both switches are wired in parallel. One as a back up the other.
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Old 11-29-2022, 08:26 PM   #7
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Swap the two relays you found to see if problem follows one of the relays.

Use a 12 volt test light at the bulb to see if there is sufficient voltage/current to make it light up. If the test light does come on, put your test light onto the ground side of the light. If it comes on but dimly the ground side is defective.
I didn't swap the relays yet, but did get the dim test light on the GND side of the receptacle. I scraped at the receptacle lead and bent it inward a bit, and the brake light now works! I still think there may be a further ground issue, but have not yet traced the ground wire, as it disappears up into a cable bundle.

Thanks, everyone!
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Old 11-30-2022, 04:50 AM   #8
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Chasing a ground like than can be quite difficult. In some cases, just splicing on a new ground wire and running it to someplace you can find will solve the issue.

You could have used a voltmeter for the same test but it is very easy to get tricked without the load of a light bulb in the test light.
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Old 11-30-2022, 08:40 AM   #9
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All good suggestions thus far.

Food for thought, another angle….Don't chase ghosts.

It could be either the 12vdc feed or the ground circuit.

To figure out which one hook a DVOM ( volt meter) negative lead to the battery negative terminal or a known good ground ( by testing with your DVOM meter first to be sure )

With your negative meter lead hooked to the negative battery terminal or a known good ground, have someone press the brake pedal and hold it down ( circuit loaded ) and then test circuit in question at the leads going in to the socket with known good bulb installed and the brake pedal pressed you should have battery voltage at one terminal that would obviously be the 12vdc feed.

Then with the circuit still loaded brake pedal pushed down good known good bulb installed, check the other wire at you bulb (the ground ) and the voltage should be @ and not over .5 VDC

With no 12vdc with brake pedal pushed you have a bad power supply.

If you have over .5VDC on the ground wire circuit loaded, you have a failed ground circuit and now you have a known direction to go and are not chasing a ghost's .

You now won’t have to chase your coach and try to find the many gang ground locations and when you do so won’t be saying “it looks good to me” or taking then all apart and cleaning them.

remember that if you have over .5VDC on the ground circuit when it's loaded you have a ground issue's .


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Old 12-02-2022, 10:15 PM   #10
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RobRoy,

Thanks for the detailed reply. For now, and after a 300 mile trip, my issue is gone. But I suspect this gremlin is just snoozing and will be back before long. I'll try your 12VDC and .5VDC checks.

Paul
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