Deuce Service Brake Lights Fail After Short

[SteveKuhn]

I honestly tried to figure this out from thread searches, TMs, and attachments. I'm not making enough headway. This is a rewrite/update from one I placed in (and just deleted from) the Deuce forum a week ago. It didn't get any action.

When I bought my truck, it had Truck-Lite clearance lights installed and a Tekonsha electric brake controller. Until last week, I didn’t realize that they’re 12v and hooked into the 24v system just like they were 24v, without a converter or alternate power.

Last weekend, one clearance light contact shorted on the bed briefly. Temporarily, none of the lights worked. After sitting a bit, everything came back up except the main brake lights.



I assume that was the circuit breaker & a reset. The driver's side brake lights were completely dead and the curb side was intermittant, weak, and would fade. The week prior, all lights functioned properly. I have photos taken by someone who was following me.

I figure that everything survived the short except the main/service brake lights.

The rear lights now function as follows:
- Blackout lights All work (including brake lights.)
- Tail/Running Curb = OK Driver’s = OK
- Turn signals Curb = OK Driver’s = None
- Hazard Curb = OK Driver’s = None
- Service/Main Brake Curb = None Driver’s = None

IOW, the large, 2 filament bulbs don’t work on either side for brake, though they work on the curbe side for signals. Both bulbs have both filaments and neither appears burned. I’ve ruled that out as a problem.

The 12v lights have been removed and insulated. The Tekonsha is on the list next.


In the process of shooting this out with multimeter and test light, I learned that I have the old switch mounted on the hydraulic side of the airpack. Because I have blackout stop lights, I must assume that this switch is OK.


Tracing the circuit and looking at the wiring diagram, I figured out that since the power goes from the airpack switch to the 3 lever where, depending on the settings, it either lights the main brake lights or the blackouts.


Today I replaced the 3 lever switch with a new one, thinking that the ‘Service’ side of the switch was fried. No good. The lights still function as above.


The only other component that I can think of that could be causing the difficulty is the Tekonsha brake controller, which is jumped into the brake light side of the airpack switch under the truck. I’m going to remove it on the assumption that it is somehow shorting the main brake light circuit. That really doesn’t make sense to me since I have the blackout brake lights. Nevertheless, it’s a possible complication that isn’t needed.


If that doesn’t work, am I down to tracing the brake light wires from the 3 position switch through to the brake lights or have I missed a consideration or two?



Ideas welcome. Thanks.

Steve

 

[cranetruck]

Hate to be the one to mention it, but the ground (returns) are all individual through the chassis and may effect just some of the lights while the (+) side to all lights are provided via the wiring.
Check your grounds!

 

[rlwm211]

It is also possible that the turn signal switch has failed. The stop lights that are for normal driving are on a different circuit than the black out stop.

This is because the blackout stop does not have a directional function and is routed through a different set of contacts in the switch.

The front turn signals are also on a separate set of contacts.

I would suggest taking a look inside the turn signal switch and look for burned contacts or evidence of over heating.

I am making these assumptions looking at the wiring diagram in
TM 9-2320-361-24-2 on Page 1129

This is just a my best guess working with the information you have provided and hopefully the wiring diagram is faithful to the actual situation.

Hope this helps

RL

 

[dabtl]

I will go with Bjorn on grounds for $10.

 

[gimpyrobb]

Yup, check what has been posted. Clean the grounds at the lights first, then open the turn signal controller and see if there is any char marks. Sounds like you had a +wire contact the ground directly. That will make any questionable grounds very apparent(as you have found out).

 

[SteveKuhn]

Yes. It was a hot wire on the clearance light straight to ground on the bed. These answers make sense. I didn't pick up from the schematic that the turn signal switch was out of the circuit on blackout settings.

The tail light assemblies ground all lights to the frame via the mounting bolts, correct?

I'll need to look inside them more closely at the socket grounds as well as the assembly ground. I'd think that the whole assembly (not just brake lights) would be flakey if a common ground was at fault.

Thanks, all.

Steve

 

[rlwm211]

From what I could tell from the schematic and I am not going out to look at my truck as my knee is barking pretty bad today, the rear lights have a separate wire ground but the fronts ground through the light itself.

That is what I saw in the diagram.

RL

 

[SteveKuhn]

Thanks for all the leads and the extra couple of explanations of 'why'. It's been a looong time since I've read wiring schematics. The comments have been a big help in getting the cobwebs cleared. A good look at the actual units will probably do the most good. I'll have some time beginning Friday to work through it.

1. Below are extracts of the airpack switch from the TM above and a CAD drawing I found on the site. The airpack switch has 2 individual wires (both #75), neither is marked, and it's not polarized. Didn't see any markings on the switch itself. There is a documented input/output. Is there a good way to tell input from output? A plain switch will work even if wired backwards. I'd much prefer forward.

2a. I want to make up some jumpers in the meantime, including a long ground to clamp directly to the batteries and lamp sockets to eliminate open grounds. That worked great last week with the meter and probe but the battery jumpers I was using for that are a tad big to fit in the tail light housings.

2b. I'm now searching locally for some fast-to-get male & female boot connectors with wire attached. Anybody ever see them at NAPA? I read about jumping the airpack switch to relieve Soldier B from brake pedal pushing duty. She'd prefer baking. Alternatively, mebbe some alligator clips will work. There are a couple of other places i want to use them, too.

3. The more I think of it, the more I like the turn signal switch as a possible culprit.

4. The brake controller being in the circuit is a real good place for trouble to be hiding so it really needs to come out. Just a lot of wires to trace in the process. There isn't a civilian trailer connector on the truck. I'm hoping I find that the trailer end of the wires never got connected. I dread finding that they've been jumpered into the military connector at the back.

 

[G-Force]

Steve,
It looks like the turn signal switch might very well be the culprit since you have no brake lights. The stop wire (#22) runs from the 3 lever switch to the turn signal switch in the diagram (wire #75 is from stop light switch up to 3 lever then to turn signal switch). I'll bet your problem is some overheated contacts in there. PM me if you need help or a better wiring diagram printed out. I might be able to get it done at work.

 

[gimpyrobb]

The brake switch is an open/closed type. No polarity to worry about, its just like a light switch on the wall, on or off.

 

[SteveKuhn]

G-Force - I followed your explanation through on the schematics I have and it helped even more. My diagrams are fine for this. I did pick up the letters on the turn signal switch so I hope I can locate them when I open it up. I lean toward the switch, too but I'm not gonna ignore the ground possibility.

Gimp: Got it. Thanks.

Steve

 

[rlwm211]

Steve You can check the operation of the turn signal switch by unplugging the rear lights, and probing the harness for operating circuits. The circuits are numbered and you can get a chart of the circuit number and function so you can be sure the turn signal switch is in fact bad.
With the other cobbed up things on the truck I would want to verify that the wires are connected to the correct bulb in the light.

RL

sorry I did not think of this earlier.

 

[SteveKuhn]

No problem. I actually did a form of that with a test probe and a meter last weekend. That's how I figured out that there was a problem up front sending juice to the back and started with the 3 Lever Switch.

This time, I plan to check the turn signal switch internally with a probe after I open it up and go forward or backwards from there. Once I can get into the truck again, I now have a much more edjamuckated view of how to proceed.

I'm fortunate to know that all the stock back lights (signals, flashers, brakes) were working perfectly a week prior during the Toys for Tots convoy. I've since talked to the guys who were following me and one had this picture of me w/ & w/out brakes on. That was before the short.

Note that the center 12v clearance light had already burned out.

 

[SteveKuhn]

Well, I got the turn signal switch apart today and it definitely took a hit but nothing is really melted or obviously shorted. That light still works but it's black as the devil.

I'm going back out to go over the components w/ circuit board cleaner and some contact abrasive because the crap on the board could definitely short it out.

Also gonna put a meter and probe across the lettered contacts per the schematic to see if the circuits pass electricity across the poles.

Will check back a bit later if anyone has any comments.

Gonna go after the brake controller box too.

 

[nk14zp]

Do the blackout brake lights still work?

 

[SteveKuhn]

Yep. Will post some update pictures later. They're on it.

Steve

 

[SteveKuhn]

So I just got done ordering a turn signal switch. But not before getting some success and a clear indication that at least part of the problem was in the switch. After cleaning the board, I got my right rear turn, hazard and stops back strong. Initially they were weak and intermittant and finally failed at the point this post started.

Although all the switch points look clean, I'm going to go over them with fine abrasive just to be sure and resolder at least 1 contact on the (far left in the picture above) that looks either cold or a bit melted off, then clean the board itself some more. If that works, I'll keep it in and hold the new one as a spare.

I also located the rear harness connection and although it would probably be a real good idea to open it up and clean it off just in case something happened there, it's a LOT easier to clean up and swap the switch and hope that'll git it. I'm not eager to drop the spare and start on that 'cause I know it'll be a bear to open up. Probably never has been.

As for the rest of the testing, I went through stuff from this thread and others. After cleaning the switch, I jumped the air pack switch out and made a long ground wire direct to the battery. I tried the probe grounded to that on the switch board and couldn't pick up juice at the documented contacts.

Went to the left tail light and checked the blackout light (bulb and probe) and the test worked. Moved up to the stop light - nothing. Tail light? Fine. The probe LED is a bit hard to make out but it's on/off as above.

Grounded the bulb mounting direct to the battery and still nothing on the stop with probe or bulb. I also checked and the ground inside the composite grounds to the frame via the bolts. Upper and lower ground to the inside of the composite in separate locations. The composite is clean and shiny w/out corrosion. Inside grounds to frame have great continuity.

All this with the new 3 lever installed. I'll test the other after I get this straightened out and if it works, the new one will be a spare.

Since the left is the big problem, I focussed only on it. I picked up on the right being fixed at the end of the session when I put everything back together and ran through the switch positions.

Also disconnected the Tekonsha controller from battery and air pack switched line. It was powered by 1 of the 12v batteries. It's only connected behind the trailer socket. They apparently took running lights for the trailer off the bed clearance lights and connected to #27. They cut #23 and put the brake wire on it, leaving the harness end sticking up. Guess they either had or planned on hot wiring an original connector for the 12v trailer brakes. I'll clean that up next but right now it's not doing anything.

Not out of the woods yet but not nearly as lost as I was.

Thanks to all and if there are any other ideas out there, I'd be grateful for them.

Steve

 

[rlwm211]

I had one of my tail light sockets fry or rather the plastic that holds the connections melted and the light kept shorting out. You may not have the short, but there could be some issues with the contacts for the bulb in the socket itself.

I understand that this may not have any particular connection to your situation. Mine was caused by my brake lights staying on and over heating the stop light socket whcih apparently run much hotter than the running lights do.

I hope you get your situation sorted out in short order.

RL

 

[SteveKuhn]

I haven't been hands on very much in vehicle mechanics and electrical but I've spent 45+ years with electricity from the band business to computers. It can do all kinds of weird stuff. For example, I haven't ruled out a hidden gap inside that pinned connector in the turn signal switch or harness connector. Not likely but possible. I've seen stuff like that.

That's also why I started looking seriously at the harness connectors in case these steps don't fix it. I try not to discount anything, just prioritize by the most obvious and in the case of the truck, easiest to get to when the weather is in the 30's and I have only a day or two or less at a time to work on it.

Weird is why I took out the Tekonsha. It was wired in at places that should affect both b/o and service lights so the likelihood of it being the source of only the driver's side was low. Nevertheless, it was 12v, hacked in, and unnesscessary. Simpler system with it out.

Since the b/o lights are working and I now know that the ts switch is out of that circuit, capable of affecting lots of stuff, and is easy to get to, it was a logical choice, worth some add'l work to try and fix, and replacement.

That doesn't mean that there isn't something else lurking. Getting the curb side to work doesn't mean that the driver's side isn't a different problem.

That's why I appreciate all the ideas that popped in here. It pays to have the tree shaken and experienced pointers when you're doing process of elimination. The down side of this for me is possibly spending $150 or so for parts that weren't the problem. The upside is having spares and a friend or two with tables at the swap meets if I need to convert them back to cash.

In your case, the stop/turn/hazard bulb has 2 filaments so it makes sense that it would run much hotter than the tail lights.

Happy New Year to all.

Steve

 

[SteveKuhn]

Happy New Year - All Fixed

The main problem was all the crud on the circuit board in the switch. Back the the day, we called this a 'flux short' or 'carbon short' when a tube blew in your Fender BandMaster amp and splattered the board.

Spent the warm, sunny afternoon with a nail board, pen knife and dentist's tartar pick between the contacts to clean it up and it worked fine through every conceiveable test at every step of reassembly.

Put in the old 3 lever switch and the lights went batty - stuff like right front turn signals on and left front turn signals off with no blinkers engaged on service drive. No time spent on playing - back in with the new switch. Maybe later with the meter and schematic.

So my 1st instinct was right - that switch was shot. But it still took the advice about the turn signal switch to clear it up. 2 problems at the same time.

Thanks to Art Swain for the 3 lever loaner. Art, I now owe you for a replacement. Thanks to Troy Kluthe for getting the backup turn signal switch in the USPS priority mail on New Year's Eve morning. Many thanks to all for the help and advice and chance to think this through with y'all.