Newbie tail light question..

I tried to search for the issue that I'm having (has already helped me with a few other things) but I didn't see anything like the problem I'm having.

The problem : My tail lights work fine, but only the passenger side break light works. The turn signals also work fine. I've found a couple of wiring diagrams through my searching, but I can't make out the wire numbers so I'm not sure what circuits I should be looking at. One thing I did notice is that it looks like the break light and turn signal are powered by the same circuit in the diagram I have... is this correct?

Before I go blindly chasing wires I thought I'd post up here and see if anyone had any suggestions as to where I should start looking.

Thanks!


By the way, this site has a TON of info... I'm glad I found it!


Oh yea... I should probably have stated that this is on a 1970 M35A2.

I also forgot to mention that I tried moving the bulbs from one side to the other with no effect.

Check the grounds on the one that isn't working.

Attached is a good dwg. of the M35 wiring diagram. I understand there are a few errors, but they are fairly minor. One thing to be aware of is there is a circuit breaker in the light switch.

The brake/turn signal light do get power from the same wire; on the left side it is #22 which come from terminal C at the TS switch. When the TS switch is in the neutral position, the internal contacts are set up so the power to the brake/turn signal light comes from the brake stop switch. When the TS is activated, the internal contacts from the brake stop switch are broken and the power to the brake/turn signal light comes from the TS flasher unit. Since your TS and the right brake works OK, but not the left brake, the problem may be in the TS switch. I was able to take mine apart, so yours will probably come apart too. I'd look for a bad or bent contact.

Good luck!

-Russ

Thought I should add a bit of clarification: the stop light and TS light are the same bulb; the power to the bulb is constant when in brake mode and the power is on-off, on-off (from the flasher unit) when in turn signal mode. So since the bulb lights when in TS mode, the problem is probably in the TS switch.

Check the grounds to both tail lights first. It's easy to do, and is a well known culprit in electrical gremblins with lights..

I don't think it is a grounding problem because the stop/turn bulb blinks when the TS is operating. A grounding problem would mean neither the stop or turn light would operate because it is the same bulb. Because it is only the left brake that doesn't work, and the right side brake does, then the problem should be in the TS switch and that's where I'd be looking. But I could be wrong, and it wouldn't be the first, nor the last

-Russ

Thanks for all the replys and suggestions! And thanks for the excelent wiring diagram rsh253! I can clearly read the wire lable now!
I'm away from the truck right now, but I seem to only remember 4 wires going into the tail light housing... is it grounded through the mounting bolts or should there be another wire?
I'm going to disassemble the TS switch tomarrow and check for any faults. I'll post up what I find (with photos ). I'm guessing I'll probably have a few more questions as well.

Thanks again for you help so far!

I'd be interested to find out what was wrong. That wiring diagram is great. All the others I'd try to use were tough to read. I'd like to be able to personally thank the person who drew it.

Where abouts in Oregon are you? We lived in the Portland area for 26+ yrs., my daughter just moved to Eugene, and my sister has lived in Grants Pass for over 30 years. We really like the Carolinas, but miss OR too.

I'm in the Portland area... right on the edge of Hillsboro and Aloha and just south of T.V. Hwy. I've been here since April '04... Phoenix before that.

That's quite a switch in weather. We lived in Tigard a couple of blocks from Tigard HS. We lived there from '88 to '04 when we moved to Seattle. We've been in Charlotte NC since March. Seattle is great, but we're really enjoying the weather here and the area too. But you can't beat a nice summer day in the Portland area!

Well speaking of nice summer days in portland, today is starting out rather nice... nice enough that I decided to tackle my breaklight issue as soon as I got off of work this morning.
And... IT'S FIXED! I started with the easy stuff... checking the grounds and connectors at the light itself. All was good there. Next I disconnected the turn signal switch plug and check the continuity of the wire going from pin "C" to the break light and that was good as well. That left just the turn signal switch. I removed it from the column and started disassembling it. Wow! That is one simple setup inside! Kind of like a manually operated relay. Anyway, I found some carbon buildup on one of the contacts... guess which one... yep, the left break light contact (pin C). A little sand paper and a pair of needle nose pliers and they were shiny as new. I ended up doing all of them just for good measure.
The result? I now have fully functioning break lights! And they seem a little brighter than before as well... may have been some buildup/dirt on the other contacts as well.
A big THANK YOU for all the help! Especially rsh253 for that diagram. It saved me a lot of time!

--Dan

Hey Dan,

(Now that I'm no longer a web-foot and am a Southern, I trie to start with "Hey........".)

That's great!

I'm a new deuce owner too and have found this site invaluable. The folks here are great and very knowledgable.

Welcome to the hobby!

-Russ

PS Pls. don't ask how I learned so much about the TS curcuit. My problem wasn't so easy to fix!!