M35A3 Taillight Malfunction

[captcarc]

Hi. I just bought a nice M35A3 with taillight malfunction. With lights on and with lenses removed from both lights, each large, bottom bulb (1683) is burning bright with both filaments lit. Directional signals blink both filaments on the same 1683 bulbs, on-and-off. Depressing brake pedal has no effect on taillights. The smaller (1251) bulbs don't fire at all at any time. I'm hoping for miswiring and not a bad brake switch. Any ideas/tips? Thank you very much. Frank

 

[RAYZER]

Most likely the brake switch.
Take the two wires off the switch and jump them together, see if your brake lights come on then.

 

[captcarc]

Thanks Ray. Do you think the smaller 1251 bulbs are brake bulbs? Frank

 

[RAYZER]

Not sure, but check and make sure their wired correctly at the back of the light.

 

[captcarc]

How do I do that? Is there a diagram or something available? I haven't looked closely at the back and the wires yet.

 

[RAYZER]

The tail light wiring is easy to check, the wires are numbered.
Try the brake light switch wire jump first. I think
the switch is located on one of the airpacks

 

[doghead]

Both bolts are used as grounds, one for the brake light and one for the tail light. Clean them both. Use a jumper wire to ground ether one of the bulb sockets to test for a bad ground.

The larger bulb is the brake light.

The bulbs have 2 elements for redundancy.

 

[RAYZER]

How do I do that? Is there a diagram or something available? I haven't looked closely at the back and the wires yet.

There are technical manuals you can download from this site.

 

[captcarc]

Thank you very much for your help! I don't know what an airpack is or what that looks like, but I may have seen the switch while creeping underneath. I'll try the jump early next week. Thanks again!

 

[captcarc]

Thanks for the info on filament redundancy. It's interesting that you say that the large bulb is for brakes because now the large bulbs are lit as running lights and blink as blinkers. If they are also brake lights, then I still have small bulbs that do nothing. It is my opinion that the running lights seem too bright right now.

 

[olbucksnort]

I got the same problem but no brake lights when headlights are on it looks like the tail marker bulb is the brake . I just got a do some tracking wires ; crawling ; digging around AND no driving around after dark. OK, go ahead , I am ready to be Analyzed by everyone.

 

[steelandcanvas]

This may help you. Line 24 should be continued to ground past the lamp.

 

[olbucksnort]

Thank you. I'll make that my first to check out; in the morning.
My check list keeps growing for the Rausch Creek Rally.

 

[The King Machine]

The signal switch on the steering column was the culprit on my A2 for my brake light issues. The single switch interrupts the break lights in order to have the bulbs flash while holding the brakes. It caused the tail lights to stay lit up, regardless of brake switch condition. The contacts were corroded inside the signal switch.

I always start by checking my grounds first.

 

[olbucksnort]

That could well be. Its original looking from 71' and it's been acting up a little this summer. It doesn't stay flashing very long on left turn signal.


"Doc. I only see Spider and Web when I look at Electrical Drawings."

 

[steelandcanvas]

That could well be. Its original looking from 71' and it's been acting up a little this summer. It doesn't stay flashing very long on left turn signal.

How did everything work out? Like The King Machine said, you may also have some trouble in the turn signal switch, the contacts can become corroded and will give you fits. Open it up and shoot a little contact cleaner in there, then blow it out with compressed air.

 

[olbucksnort]

Everything is working good now. The new Signal Switch held the current enough to show weak grounding on the tail lights as well, also someone reversed the bulb wires on front left signal lamp and a loose ground to the N/A black out light.
To sum it up : I got spare parts now and everything Happy Happy!

 

[armyfred]

My M35A3 brake lights are inoperable. So, after searching, I found this thread that appears to address some of the issues I have. When I disconnect the cannon plug at the turn signal switch box and check the voltage on the lead coming from the brake light switch, with the brake pedal depressed, I have 24 volts. However, when I reconnect the plug and check voltage inside the box on the brake light wire, I have only 1 to 2 volts. I have repeatedly checked pin connections for contact. Any suggestions. Thanks in advance.