Tail light converter

bigredhdt · September 28, 2015

A few months ago I posted a topic about my 2007 Volvo 630 turning on the hazards and headlights when I stopped the truck and turned it off. After having the terminal strip melt in my 3 relay converter, I went to the 4 way. Just by accident I found my problem. Pulled out a ring to tie a horse and it was almost too hot to hold. Opened up the wiring channel and I saw that the wires to the led tail light were free to rub against metal and most likely did that causing the short

This truck has the lcm rather than fuses. I was thinking I should connect fuses on converted outputs,and running lights (already have power fused in the tail light converter enclosure.how are the rest of you protecting your trailer wires?

Ronbo · September 28, 2015

I run mine through a jackalope from Henry

Jack Mayer · September 28, 2015

The Jackaloppe is the best turnkey solution available. Period.

You can replicate its function pretty easily, but by the time you do, you may as well buy the Jackie. One thing you "might" add to the Jackie is fuses on the output side, which serve (only) to protect from a backfeed (or short) in the trailer entering the Jackie/truck systems. But that is not really necessary - the relays in the Jackie are (I think) 60 amps and can take abuse. Plus they are easily replaced if required.

bigredhdt · September 28, 2015

The question is to protect the trailer wiring. If you look at the schematics, the trailer lights are directly tied to the lcm. The lcm is supposed to manage wire protection. My trailer does not have #10 wire from the plug to the LEDs nor does it need it. I would guess that most non commercial trailers today don't have large wiring either. I could have Volvo reprogram the lcm at the cost of $400. I think not.

I agree in principle about buying the jacalope vs relays, but the consensus is that it should go in the truck. I did not want to make 2 more penetrations. I suppose I could have put it in a Hoffman box, but that's almost as much work as doing the relay method. Now after discovering the limited protection of the lcm, that's another reason to not use the jacalope as it doesn't appear to add any more protection.

Nuke-E · September 28, 2015

There are a couple of things worth thinking about out here. First of all, all of the lighting circuits are still fused--there are a total of 6 fuses for the various LCM-controlled functions, which are simply given numbers 1-6. All are 10A fuses, and protect different functions (I don't remember which is which off the top of my head). If there's a short that would carry more current than what's allowed, the LCM should intervene before the fuse blows. The marker light circuit, however, is separate from the LCM with the lights turned on/off via relay. I'd me more suspect of that circuit being involved with your problem--bigger fuse, on for extended periods of time, and no "smarts". Regardless of which circuit it was, it doesn't take much to generate enough heat to melt stuff.

bigredhdt · September 28, 2015

I looked at the schematic I downloaded from Volvo and didn't see fuses on the schematic or fuse list. I did look in my truck on the fuse box. I only see 2 trailer fuses. A 30 amp for trailer stop and 20 amp for running lights. Can't find an ICC or left/right fuse. Obviously, those are too high for the wiring in my truck. Without finding left/right I will need output fuses to power trailer. This might be a good thing to add to the hdt starter document.

Nuke-E · September 29, 2015

The left and right trailer light functions are controlled by the LCM. They're on fused 10A circuits shared with other functions, and the LCM will cut power at far less than that.

bigredhdt · September 29, 2015

Sorry, not seeing it on the schematic. They look to be directly connected to the lcm, circuits 112c and 113c. Now I see the stop and running are on relays controlled by the lcm. I don't see any 10 amp fuses feeding the lcm at all.

Nuke-E · September 29, 2015

I just went back and took a look. They aren't 10A fuses--I'm not sure why I thought that. They're either 25A or 30A--fuses 8,10, 16, 42, 45, and 49.

ray.service · September 29, 2015

A little more info

PV776-TSP174408.pdf

bigredhdt · September 29, 2015

I just went back and took a look. They aren't 10A fuses--I'm not sure why I thought that. They're either 25A or 30A--fuses 8,10, 16, 42, 45, and 49.

8,10,42 are input fuses to the lcm. 16 is a key fuse, 45 is the "car" horn, 49 is aux.

From the schematic, I see f43 is the stop fuse @30 amps. F9 is the marker lamp fuse @20amps. I still don't see fuses for left/right and ICC. I assume the lcm is providing some type of solid state protection, but how can you know it's output limit? Just to verify, I'm going to ground one of the turn outputs and see what happens.

30 amps for stop lamps is too high for 14 gauge wire. Should be 20 or 25. 14 is overkill for LEDs anyway.

Nuke-E · September 29, 2015

It looks like they've changed the fuse numbers a few times. The ones I listed are the ones on my truck (a 2004 VNL300); I've just glanced at a few different diagrams with different numbers, but the same labels. Keep in mind there was also a recall that affected a lot of these trucks--some were originally equipped with circuit breakers feeding the LCM.

Yes, the LCM is providing fault protection. I've had customers plug in headlights backwards so that the low beam power wire was directly connected to ground--it'll show a fault, and the fuse won't blow. The limits are (within a certain range) adaptive and there's a time-dependent component--a slight overload will have to be present for a longer time in order to generate a fault. For the headlight circuits, the limit is 5-6 amps, at 10 you get maybe a second before it kills power.

The trailer stop relay does control a 30A fuse--you could change that one with little collateral impact to protect your trailer. But if you're converting to a combined stop/turn setup, that wouldn't accomplish much. The turn signals are still driven by the LCM.