BRAKE LIGHT

[Manstein]

Ok, I've got a left brake light that is inop. I have checked the ground for the housing. It's good and I have tail lights. (I think they all share the same ground) I have replaced the brake light switch and checked the wiring for any obvious damage. Can't find any. If I use my DVOM, I am getting voltage at the socket that matches the right side when brakes are applied. I also replaced the flasher because I had in intermittent blinker problem with the left side. That is fixed. I've also replaced the bulb. I tried bending the light bulb socket in just a little just in case it wasn't connecting good with the bulb. No change.

Can anybody think of something I'm missing besides a hidden broken wire?

 

[Barrman]

My first thought was the tab that holds the bulb and acts as a ground. You wrote that you bent it, but did you make sure it was clean of gunk enough to make a ground to the bulb?

Try running a wire from the bulb body to one of the cover mount screw holes.

The bulb socket itself has the single contact in the middle with battery positive voltage. Has the little plastic thing behind it broken off of gotten squished so much that it isn't touching the contact on the back of the bulb?

That is all I can think of. You have power to the contact and ground for the bucket. The problem has to be either + - at the bulb.

 

[CGarbee]

In addition to the comments above based on a similar situation on a couple of my trucks...

I've actually had more than one housing that did not have shared grounds... Solution for me was to pull both mounting bolts and clean them both up, the threads in the housing, and the contact area on the mounting bracket... I'm also a big fan of dialectric grease both for the bulb contacts and for the mounting bolts/contact surfaces and apply it whenever I'm working on my lights...

 

[acetomatoco]

Correctimondo.... There are two separate grounds in the composite lights... each bolt of the two hosts some functions...ACE

 

[Manstein]

Update

Looks like my DVOM is not operating correctly. I secured another one and found that I'm getting about 3 volts at the socket. Looks like I'm looking for a corrosion/connection problem up stream. Any ideas?

 

[devilman96]

Im leaning towards grounding issues just because I know what a pain they usually are on these... However if your SURE you have a good ground check the split made at the trailer pigtail... then jump to the plug connector between front and rear harness and see what you have... This will tell you what section of the harness you need to concentrate on... Don't over think it though... Electrical problems are usually simple!!!

Print the attached PDF's and tape them together... and or use the cad, its easier to read but hard to print..

 

[alphadeltaromeo]

Dman - thanks for posting the CAD PDF...I needed this too!

 

[devilman96]

Yeah I cant remember whom did that file but its a nice one to take to Kinkos and have printed in black and white!

 

[Recovry4x4]

Peter Bogg made that up!

 

[Boatcarpenter]

If you have the TM on CD, take it to a place that does large format printing and just find the page with the wiring diagram and have them print it out 11x17 or larger. Get several copies and you are good to go.
BC

 

[houdel]

Re: RE: BRAKE LIGHT

I''m also a big fan of dielectric grease both for the bulb contacts and for the mounting bolts/contact surfaces

You of course meant CONDUCTIVE grease; a DIELECTRIC grease is an insulator. A very common mistake.

"From Wikipedia, the free encyclopedia - A dielectric, or electrical insulator, is a substance that is highly resistant to electric current."

 

[Manstein]

Well, finally got back to this brake light issue. Garbee was right about the bolts. I removed the housing and brushed the star washers and bolts and presto... the junk works. UNBELIEVABLE!

I wanted to post the fix cause I hate threads that don't end with a solution.

 

[CGarbee]

I wanted to post the fix cause I hate threads that don't end with a solution.

Glad to hear that you got them working. Appreciate hearing what the fix was and getting some closure on the thread.

 

[cranetruck]

Re: RE: BRAKE LIGHT

I''m also a big fan of dielectric grease both for the bulb contacts and for the mounting bolts/contact surfaces

You of course meant CONDUCTIVE grease; a DIELECTRIC grease is an insulator. A very common mistake.

"From Wikipedia, the free encyclopedia - A dielectric, or electrical insulator, is a substance that is highly resistant to electric current."

I think Cabell actually meant dielectric grease as in non-conductive. The grease helps prevent corrosion, the metal to metal contact still results from the pressure and twisting action of the components.
Using a conductive grease could cause all kinds of problems, bridging insulators and creating shorts.
I use non-conducting dielectric grease on light bulb sockets, connector sockets etc.

 

[rampli]

RE: Re: RE: BRAKE LIGHT

I ran into the same problem with the lights on a M103 trailer. Why are the two mounting bolt holes not common inside the light housing? Anyone have an idea?

Cranetruck, never thought of dielectric grease as an insulator.... You are correct, a conducting grease would cause all kinds of problems. Thanks for the awakening! The biggest advantage to dielectric grease is not needing to find those pesky needle nose pliers when it is time to extract the bulb base after many years of service.

 

[cranetruck]

RE: Re: RE: BRAKE LIGHT

Checked two plastic housings and only one of the mounting screws serves as a ground. There is a 50-50 chance of having a bad ground if one of the screws is loose or not properly grounded to the vehicle.
So it would make sense to advise that both mounting screws are tight rather than to try to explain that only the one on the passenger side need to be making a good ground. Then again, different manufacturers may have different solutions.There are 3 separate schock mounts to ground.

Metal housings do not have this potential problem.

For all about grounding, see next MVM issue, should be out next week.

 

[acetomatoco]

RE: Re: RE: BRAKE LIGHT

The overall design of the composite lite is money... costs a lot more to engineer and design...and of course some pinhead designer figured that having separate grounds would keep some of the light working if one failed... Your job as taxpayer was to pay as much as possible for everything..... The failure to keep water out of the composite light was the big booboo...the stainless screws welding themselves to the inserts in the cheap plastic housing was another brilliant maneuver...no antiseize used... a single latch and gasket like used on an ammo can would have solved the problem... Have you seen the new composite lights with the diecast housing? Two screws are phillips head and the rest flat blade... now you need two tools to change a bulb...!! How about the new electronic light switches which you cannot operate in a blackout situation by feel.. 422 buttons and lights and hundreds of dollars and all they do is burn up and confuse operators who have to look at them while driving to operate them...and summarily run off the road.. the older 3 handle switches lasted from 1950 to 2000 with no changes to speak of... (the M880 model with the dash light resistor which burned out because it was only 12 V capable excluded)...and would last another 50 years if some Senator's cousin hadn't bought a switch company and got a pork contract for the new improved switch.... end of rant... ACE

 

[Boatcarpenter]

RE: Re: RE: BRAKE LIGHT

To quote Cranetruck "Some things can't be made better, just differently"
BC

 

[cranetruck]

RE: Re: RE: BRAKE LIGHT

Thanks BC, look at women for example.

Good rant ACE, just try to flash your head lights while driving with the push button switch, don't think there is an easy way. With the 3-lever switch you flick the lower lever from dim to park and back (no locking action).
Like I have stated before, it took at lot more brain power to design the 3-lever switch than the bushbutton mistake.

 

[Boatcarpenter]

Brake light

I think women are the best example Bjorn
BC