Brake Light Ckt Help?

[ItBites]

All,

Please help, cause I hate electrical problems. I am sure I could find the problem with enough undoing harnesses and testing, but I thought one of you folks might know right where the problem likely is.

Here are the clues:

My Brake lights do not work. Additionally, the rear Hazard flashers do not work (but the fronts do, so I think the hazard flasher unit is OK and I would also think the hazard switch in the column is also OK?).

The rear turn signals (as well as the fronts ) do work and at the rear use the "bright" filament (1157 bulb) that the brake light and hazard flashers would use if they worked, so the bulb is good (I also ohmed the bulbs - both - just to be sure). This also indicates the ground at the bulb socket is good. Also the "dim" running light filament works, so again the ground is good at the light socket.

The brake light switch under the dash has 12+ volts to it on one side and not on the other when the pedal is not depressed (should be correct - no volts from the switch to the brake light). The switch has 12+ volts on both sides of it when the pedal is depressed, which should provide power to the brake lights - ??except something is wrong between there and the brake light??

WTF is in the path after the switch at the pedal??????

I am thinking the turn and hazard flashers have to be in the loop somewhere since the brake light goes intermittent when turn signal or hazards are invoked? but not directly in the loop. Here is where I lose understanding:

I pulled the hazard and turn flashers and they are of the two-prong variety, so there are not multiple circuits thru them and as I said before the turn signals all work and the hazards in the front work, so I think the flashers are OK. I also ohmed them out and the each had about 45ohms impedence, which is relatively low and should allow volts to the brake lights if it normally goes thru one of them, but if it did, you'd think it would excite the bimetallic switch and then flash, so it cant just run thru the flashers on a normal basis, so how does the turn signal interact?


The reason I am looking for a device in the circuit (rather than a broken wire) is because the hazards AND the brake lights do not work, so the clue is that something common to those circuits is bad.

I also suspect the wire to the light from the dash region to the "bright" filament is common for the brake light, the hazard, and the turn signal (which works). If this wire is common (since it goes to the same filament), then the problem lies somewhere between the brake switch and the combined line running power to the "bright" filament. This is an assumption, but the turn signal does work.

Anyhow, if any of youse have any insight, I'd be mighty beholden.

[ItBites]

Anyone?

[NROTOXIN]

Do a continuity check between the switch (none 12vdc side) and the brake lamp with an ohm meter, that will tell you if anything is in the path (few ohms) or nothing (open/infinite ohms)......that would be a good start.

curtis

[Ron61]

Curtis gave you a good starting point. I had a similiar but not exact situation on mine. Do you have the seperate round lights on the rear or the single long ones? I finally traced my problems down to a high resistance ground somewhere in the wiring. After much delebiration, I looked in the wiring schematic and found the lead numbers and where they multipled. I then went there and cut the ones to the rear off and ran new ones from the other side of the connectors. They have worked great ever since and that was in 1997.

Ron

[John Poling]

itbites,

Is this a problem that just started? Did they work okay before? What are you using for the turn signal switch? What column are you using?

John

[ItBites]

Thanks for the look at my issue:

The taillights are the twin over-and-under round ones, and the brake light is the "bright" filament in the lower (1157 bulb) one. It is the same filament used for the turn signal light.

This problem is new. The car was built in 1992 and has always had working lights. There has been no damage to the car that would clearly cause an open in the circuit and no wires hang or are obviously subject to pulling or damage. Anything is possible, though, and I rule out nothing at this time.

I'll check the continuity from the low side of the pedal switch to the bulb socket, but I think I'll find that is an open.

The ground to these sockets seems OK since the turn light works (same filament, same bulb as the stop lights) and the running lights work on these sockets as well (same bulb, "dim" filament). The ground is the actual socket portion, so I think if the ground is OK for those functions, then it should be OK for the stop light as well.

The column I am using is from something like a 59 GM bob-nose truck (or something like that). The turn signal is the one that is a part of that column as is the hazard switch. The turn signal turns the "bright" filament on-off when the brake is depressed as well as when the brake is not depressed, so I think it is OK. The hazard switch runs the fron hazard lights, so I think it is OK also, but things may be more complicated there - I am just not familiar with the circuit diagram for the interactive devices (brake, turn, and hazard lights).

I am still looking for something common between the hazards and the brake circuits as my biggest bang for the buck.

BTW, there are no schematics for this car, it was built as a you-build-it in the earlier days than now. The fuse box is a "Dr. K's" brand and not as nice as the ones you can get now. The wiring is black tape wrapped from one end to the other and is really a pain to get into. On the plus side, all connections are soldered and shrink-wrapped and the wire is of a good quality.

I really think there is some device failed here rather than a wire that is broken (just a hunch).

Thanks a bunch for looking at my proble!!!!

[John Poling]

ItBites,

I am not familiar with the '59 truck column but will assume it is similar to other GM columns. You should have some kind of connector that connect the electricals of the column to the harness under your dash.

1) Bad or degraded grounds are the primary culprit in all electrical system failures. My first tests would be to verify whether all four tail lights really do share one ground or whether the two that are not working correctly share a ground of their own. I would bet that this is the case. To verify a good ground for your light, make as long of a jumper wire as needed to reach your battery negative (-) terminal from the ground wire on your tail lights, this will insure that you are at a true ground. Make absolutely certain that you are probing the ground and not one of the power wires. At this point check to see if your lights are working. If they do, repair your ground wiring in the rear. If they don't work, start probing your wiring from the tail light moving towards the front and find out where you lose your power at. Over time connectors have been known to corrode and lose their connection.

A couple of other ideas are as follows:

2) If you have 12v to your brake switch, depress your brake pedal to activate your switch and insure you are getting 12v out. Trace that wire up to where you can verify that it does or does not go through the turn signal switch on your column. Check to make sure your turn signal switch is functioning correctly.

3) Start at the fuse panel and trace out from there for the flasher circuit. This could still be tied together with the brake lights at the switch in your column.

In closing, electrical problems are the most difficult problems to diagnose because of all the loose, broken or corroded connections that are found in a typical automotive electrical system. I may be weird in stating this, I love to trouble shoot electrical gremlins as long as there is not electronic componants in the system. The only thing I like better is to put the system together from new, as to eliminate the probability of some of these electrical gremlins.

Please let us know if/when you need more input.

John.

[Dirty Harry]

I'm looking on with interest. You see, I have a Dr. K wiring harness and I have the same problem, but I have the single tail/turn lights. I even called their number back when I first encountered the problem and whoever I talked to couldn't even believe it was happening the way I described. So--if we can get to the bottom of this, it will help both of us. I found that if I unplugged the brake light switch completely the rear hazards would work again.

[ItBites]

Harry, Can you give me Dr K's phone number and I'll call them and maybe with the both of us reporting similar problems, they will put a little more thought into this.

Looking at Dirty Harry's reply above, I tend more to think there is some device here that has failed, rather than a problem in the harness itself.

I'll post when I have done more investigation and have more to say.

[Dirty Harry]

It will be tonight late or tomorrow before I can find the information (I hope) and get it to you. The person (Dr.?) I talked to was not real helpful. The reason I didn't press harder was that I had had the harness for 2-3 years before I put it in, so I didn't feel like I could force the issue much. I just opted for functional brake lights instead of 4-way flashers. I have 2-way flashers when the brake light switch is hooked up. I never figured it out and was surprised at reading your post.

[petek]

If I remember correctly, the signal for the brake lights goes through the turn signal switch on the column. The same switch also has the hazard light switch connected to it (it's a mess).

The brake light signal gets disconnected when the turn signal switch is set to signal a turn.

Something to try: press on the brake pedal and move the turn signal lever. See if the brake lights flash on while the lever is moved. It could be something as simple as dirty contacts at the switch (or at the large flat connector on the column).

And John -- I agree! These sorts of problems can be actually enjoyable to troubleshoot ... when you've got the car right there to work on! Troubleshooting by email or phone on a car off in the distance can be frustrating!

[Dirty Harry]

itbites...
My call to them was back when I was doing that portion of my build-probably about 1996 or 7.

[Dirty Harry]

My hazard warning light switch is a toggle on the dash, not a switch integral to the column.

[ItBites]

Just wanted to bring this back to the top.

Will keep diggin. Thanks for the advice from all who have replied.

[Art Burtt]

I hate to say this but check the fuse!

[John Poling]

"Check the fuse", HMMMMMM! now there's a novel idea. That's as important of a connection as the ground, as a matter of fact without a good fuse, a good ground is not gonna do much good.

John

[Ron61]

Many good answers and it is very difficult to trouble shoot a wiring problem over the posts. If your wires are numbered or color coded that would help. If it goes through the steering collom switch, that could be a mess. If you can find the same wire from your brake switch output side try to follow it and see where it goes. Maybe look on the back of your brake light holder and see if you have the same number, color wire there that left the switch. Mine are numbered and I just happen to remember then #272 is the left turn signal in the back. If you can find a point where the wire leaves the fuse, cockpit area that is accessable and you are getting 12V through the brake switch, then take a clip cord and put 12V on the lead that should go straight back to the brake lights. That will tell you if it is good from that point back. You need to get a point that you can break the trouble between the front and back. Wish I was close enough to come over and help you.

Ron

[ItBites]

Checked the fuse and have power to the brake switch at the pedal. Power from the switch at the pedal is also present when the pedal is depressed.

The ground at the bulb is good as the bulb lights when turn signal and running light is used. The ground goes from the socket to the "threads" on the bulb and is common between all filaments (one ground for the entire bulb). Also double checked resistance from bulb socket to batt neg and have <.5 ohm.

Thanks very much all for replies.

Will be out of town til Fri night when I will be able to try to separate front from back. I think this will help. Will also look at wiring from switch thru column, trurn signal hazards etc. Also like the check for continuity from switch to bulb contact. Also like the idea of depressing brake and using turn signal (I think I did this and the signal worked, but will double check).

Will return to this thread Monday with progress.

Thanks again.

[Dirty Harry]

I've sent you some information via private message.

[ItBites]

Well folks,

Thanks for all the good suggestions. As I said, since the turns worked, but the brake and hazards didn't, I really didn't suspect the usual ground issue and since I had power to the brake pedal switch, I didn't suspect fuse, but triple checked all the obvious before digging deeper.

As I thought, the problem turned out to be a device that involved both the hazards and the brake lights - the turn signal switch!

See, the signal switch has a pair of spring wipers. One is the "null" wiper that makes contact to both pins to the rear taillights when the turn signal is not used. This wiper is fed power from the brake switch normally (thru the hazard switch by the way) and fed power from the flasher (thru the hazard switch also - this is how the hazard switch turns off the brake lights and makes the rears flash) when the hazards are turned on. since this wiper is downstream of the hazard switch and the brake switch, when it failed, neither worked at the rear, but the front hazard flashers still worked.

So, I now fully understand the interaction of the hazards, turn signal and brake light circuits. If anyone needs help in these circuits I can likely be of assistance. (Dirty Harry - respond if you'd like to get this working. PM me and we should talk on the phone...)

Anyhow the problem was the turn signal switch.

Now the problem is where to get a new turn switch for a '67 F-600 Truck column... Any ideas?

Thanks,