brake light question

[transalpian]

Greetings! 1974 Series 3 88" (LH Drive) owner here.

I've got a brake light question regarding the right side light. When the headlights are off, the brake lights work as expected. However, when the headlights are on, the right brake light fails to light. The left works fine.

I replaced the lampholder since the original was pretty bunged up. Replaced the bulb since I bunged it up on removal. Things worked great!

Next day, back to the same operations, no right brake light when the headlights are on.

Since the brake lights work (w/o the headlights on), I'm getting power to the bulbs. What changes when the headlights come on?

I'm thinking ground, but why does it work at all? The left side works fine. What is different about the right? The turn signals work fine too, both with and without the headlights on. My wiring inspections show they share the same ground as the brake light. The ground is a ring terminal, bolted to the bodywork, under the access cover.

The truck has been painted. Am I not getting "enough" ground through the connection to fire the brake light when the headlights are on? Does that even make sense?

Thank you in advance!

Jeremy

[rrc.swb]

I bet is ground issues. The body is aluminum, you should hook it up to the frame.

On my truck they grounded at each side. That's probably why the left is fine.

[transalpian]

My truck is also grounded at both sides, both in the same location (on the body). Was this OEM?

Should I re-route both sides? Or leave the left side well enough alone?


Jeremy

[SafeAirOne]

If it worked well once you replaced the socket and lamp, then I'd confine my initial troubleshooting to that area.

The rear tub is attached to the chassis by 18 bolts and the lights on the other side of the same aluminum tub (a great conductor, by the way--aluminum wires likely feed your house) are grounded just fine, so I wouldn't change/add any wires to the mess in order to ground to something physically different, but electrically the same.

I have 4 BRAND NEW rear lamp assemblies (brake and turn) on my 109 and I'm having had a problem with the brake/parking bulbs popping halfway out of the sockets because either the cheap chinese bulbs don't have long enough bayonet lugs or the cheap chinese sockets are made with a lot of slop built in. One side of the bulb pops out and the filament contacts on the bottom of the bulb do strange things with the 2 electrical contacts in the bottom of the socket. I'd check this first.

If all was OK there, I'd mess with the 3 wires coming out of the lamp assembly to make sure they're making good contact with the 4-way connectors they're plugged into. Since the parking lamp and brake lamp share the same ground, the electrical path must be good, but it wouldn't hurt to clean up the contact area between the grounding socket/clip and the tub surface even though the socket assembly likely has a second ground through one of the 3 mounting screws.

If all checks out there, I'd break out the multi meter (or test lamp for those who don't like multimeters) and start chasing down 12 volts and unintended grounds/shorts in this very simple system.

[Broadstone]

If you replaced the lamp assembly with an aftermarket one and not a genuine NOS one it is likley just getting what you paid for. I did the lamps on mine with britpart lamps and they are just junk. I have had one brake light that worked opposite to how it was supposed to. I had to spin the inner assembly to get the bulb in correctly and work correctly. The screw mounts crack as soon as you put the screw in too. Get an assistant and use a test lamp.

[transalpian]

I replaced the lamp holder with this one, from our hosts:

http://www.roversnorth.com/store/p-5963-lamp-assm-stop-tail-defender-90-110-style.aspx

I guess its time to get into the wiring with my daughter sitting on the brake pedal...

[transalpian]

Haven't got into it yet, but learned two more data points last night:

The backup light only works when the headlights are off AND goes out when the brake lights are applied. Furthermore, the rear lights illuminate slightly when in reverse.

Now, I'm a simple guy so the only connections I see between all these systems is the main ground on that side. the plan is to remove the ground attachment, clean off any paint or goo, and giver her a go.

thanks!

[transalpian]

More data, the right front running lamp doesn't light any more.

All my issues are on the right side. Is there a "main" right hand side ground connection?

The left side lights work great...

Thanks

Jeremy

[transalpian]

Update.

Dug into the system yesterday with my meter. Turns out there was no gound on the rh side. The culprit was the gound anchor point to the body was corroded AND insulated by a nice heavy coat of paint.

Cleaned it up, and it works great. All the lights, all the time.

HOWEVER, the lampholder discussed above does not fill me with confidence. The plastic is pretty soft (the bulb bayonetts gouge it pretty easily) and the tolerances are too big. The bulb can go in either direction and still engage and work! The terminals inside the lampholder needed adjustment with an ice pick to work at all. Not a really nice piec of kit, unfortunately.

Anyone tried the LED lamps?

Jeremy

[knac1234]

Jeremy,

Probably not much help, but I just put together all of that on my 72 SIII. Grounds are the key......then check all bullet type connectors for corrosion and preferably replace (I replaced ALL bullet connectors). All spade connectors too (I replaced ALL also). Bottom line is that everything I cleaned and replaced, and now everything works perfectly. Actually did that for the entire electrical system.

Unless someone has hacked into your wiring harness and been creative, or there is a short somewhere, this should cure all. I untaped virtually the whole harness, cleaned and retaped. I know there was no hacking (except a trailer harness I removed at the tub) and there are no shorts.

Not sure I understand the loose bulb question, but be sure that in those lamp holders there is a spring between the holder and the seat that keeps the bulbs tight and from moving.

Regards,
Julian