41 Cadillac tail light roulette

Started by charliemon, July 20, 2012, 11:42:09 PM

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Bill Ingler #7799

Hi Charlie: I think rather than a grounding issue I would suspect at this point the brake switch. Pull the two wires from the brake switch and using a test light see if you have power from one of the wires to the switch. If so then it is probably a bad brake switch. Better yet temporally hook both of the  brake wires together. With the battery connected, you should have brake lights. I have had new brake switches work and then don`t work, then work again. Most of the repo brake switches offered today are a bunch of crap.    Bill

charliemon

Hi Bill.

The first thing I tried was to connect the brake wires & bypass the switch, but still no lights.  I will have time again this weekend to start troubleshooting.  I'll let you know if I find anything.

Thanks, as always.
Charlie Renner
1941 6267D

charliemon

Hey Bill,

1 follow up question:  Should any of the lights work if the housings are both not grounded?  When I remove the housing, the lights still come on but they are much dimmer.  I'd say about 1/2 bright.  Something I'm often accused of.

Thanks
Charlie Renner
1941 6267D

Bill Ingler #7799

Yes you are right. When the light housing or individual light assemblies are not fully grounded you still will have some light and then when properly grounded you will get full CP from the light. Please don`t get too much more technical as I am just a poor old pilot who was once thinking of becoming an engineer and was kicked out of Purdue for grades which was caused by too much partying and chasing girls.  Have Fun     Bill

Glen

I’m not familiar with the 41, but if the tail light and brake light filaments are in the same bulb then each filament can get its ground through the other filament and its associated circuit if the normal ground is missing.  But if that happens only the tail light filament will light.  The brake light will not  come on. 
Glen Houlton CLC #727 
CLCMRC benefactor #104

Paul Phillips

Charlie
I am glad you are getting closer.  There is a possibility that grounding of the bulb is still an issue, but the best suggestion at this point is to use voltage readings to diagnose.  Doing this will eliminate false assumptions that can result from looking if the bulb is glowing dim or bright.

If you go back to the bayonet connectors in the trunk and separate the ones for brakes on both sides (the neutral colored wire with no tracer), you then connect the voltmeter with the + to a known good ground and the - to the body side of the brake wire at one side.  This will isolate any effects from the light housings.  With the jumper installed at the brake switch, you should have 6 volts at this point, and with the jumper removed, you should have no voltage.  You can repeat the check with the brake wire on the other side, just to be sure.  If that is what you see, the problem is from that bayonet connector out to the light housing.  It may be the same problem on both sides, or could be somewhat different side to side.  I would next reconnect the bayonet connectors and remove the bulb, repeating the test with the test point being the socket contact for the brake wire.  If the voltage is correct at the socket contact, you probably have a situation where the bulb contact and socket contact are not mating.  There are a variety of causes for that, but they are usually 'mechanical' about alignment or contact pressure between the two points.

If you do not have voltage at that test point, there is a wiring problem somewhere else.  Let's see what you have at that connector before discussing how to chase a problem there.

Paul
Paul Phillips CLC#27214
1941 60 Special (6019S)
1949 60 Special (6069X)
1937 Packard Super 8 Convertible Victoria
1910 Oakland Model 24 Runabout

charliemon

Success.  Thanks again to all for the help.  I checked the voltage at the wires at the rear to find zero current.  With the brake wires jumped at the switch, I had my wife go around to the rear of the car while I went back under the dash.  I found the the brake line from the harness was not well connected to the male / female connector in the main harness under the dash.  My only recourse was to use a zip tie to hold the harness against the dash support, which put pressure on the connection.  Unfortunately, I don't think I can fix the connection without removing the entire harness, as there is no room to take it apart (or even tell which wires are which) & no play in it to get it to where I can work on it.  I imagine at some point the whole harness will need replaced.

I took the car out for about 50 miles on our nice smooth NE Ohio roads and the connection is holding fine.  At least, with all your help, know where the issue lies if it comes back.

I think I'll be @ Hershey, and if you are also there, payment in cold beer will be available.  I have several friends with spaces where a cooler will be possible.

Thanks again to all.

Charlie
Charlie Renner
1941 6267D

Paul Phillips

Charlie
Great news and congratulations!  A well positioned (and hidden) zip tie is a wonderful thing. I hope you get many more days and miles of enjoyment from your car before needing a more involved repair.

Not sure if I will make Hershey, but hope to cross paths some time in te near future.

Paul
Paul Phillips CLC#27214
1941 60 Special (6019S)
1949 60 Special (6069X)
1937 Packard Super 8 Convertible Victoria
1910 Oakland Model 24 Runabout