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1970 Deville - Parking lights come on when brake pedal pressed

Started by grantatx, October 03, 2017, 11:31:37 PM

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grantatx

Hi all,

I've got one more issue to sort before I can get my car inspected - the front parking lights come on when I press the brake pedal. I've done a lot of searching on this forum and elsewhere, also looked at an online copy of the wiring diagram and everything seems to point to a faulty turn signal switch. All other lights work fine. I don't have a great knowledge of electrical troubleshooting so (rightly or wrongly) I figured the best idea would be to just replace the switch and see if it fixed the problem. The turn signal switch is the only place I can see on the wiring diagram that both circuits meet. Anyway, I purchased a repro switch from OPGI and have the column stripped to the point where I'm trying to get the switch out of the column, which is proving very difficult. So I have two questions:

1) Has anyone had the same issue, and how did you fix it

2) Has anyone replaced a turn signal switch and if so how did you remove the switch from the column?

Thanks again in advance.

Grant

TJ Hopland

Have you checked all the bulbs?  Maybe somehow a single contact got stuck in a double socket or the wrong double is installed somewhere?    Ground issues are good at making just one light act fully.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

grantatx

I did check that all the lights worked, but I haven't pulled all the bulbs. I'll do that tomorrow, thanks!

TJ Hopland

It may not be the one that is acting up that is wrong or has the ground issue.  Check every lamp and socket involved in the brake and parking lights.    Just taking them all apart to check them may solve the problem if its a ground or contact issue.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Glen

Is it the front parking lights that come on or the front turn signals that come on?  Makes a difference. 
Glen Houlton CLC #727 
CLCMRC benefactor #104

Jeff Rosansky CLC #28373

You can also just unplug the turn signal switch at the base of the column to test your theory.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

klinebau

Replacing the turn signal switch is a PITA.  You have to remove the steering wheel lock mechanism and remove the turn signal stalk.  You also have to remove the emergency flasher knob and don't lose the piece that the flasher mounts to inside the column.  After that, you must disconnect the "harmonica" connector and loosen the bolts for the steering column.  Make sure that you note where the shims are located as they will likely fall out.  Finally, you need to remove the turn signal wires from the sleeve under the steering column.  After that, you will be able to pull out the turn signal switch and the harmonica connector, but it is still a tight fit.  The factory service manual spells this out in more detail.

After you have the old switch out, make sure you compare the new harmonica connector with the old one.  I had to swap all of the wires from the new connector to use the old connector as the new connector did not fit.
1970 Cadillac Deville Convertible
Detroit, MI

grantatx

Thanks for all the responses guys! I've already disassembled the steering column to the point I can get the switch out but am going to stop and first check all bulbs and circuits as you've suggested.

Jeff, I'll try your suggestion of disconnecting the switch under the dash, however from what I can see the brake light circuit goes through the switch on the way to the rear of the car, so if I disconnect it they won't work will they? Forgive my lack of knowledge of car electrics - I'm learning as I go!

Thanks !

Grant

grantatx

A quick update - I've checked all the bulbs and everything seems to be in order. However, while doing so I noted the following:

1) When the brake lights are on it is the parking lights that are on in front, but quite dimly

2) With the brake lights on and the front indicator flashing, the parking light filament also flashes very dimly. Even when I take the light socket right out of the fitting so it's not earthed.

I've printed off the wiring diagram for a more detailed analysis but if anyone has any further suggestions I'd appreciate them!

Cheers,

Grant

grantatx

Oh, and:

3) Front marker lights come on when brake lights are on also

grantatx

Right, I think I know where the problem is. The rear side marker lights are coming on when the brake pedal is pushed, and I don't believe they should. According to the car manual and the workshop manual they should only come on when the headlamp switch is either halfway or fully on. Please can someone confirm I'm correct on this?

Thanks very much!

Grant

Jeff Rosansky CLC #28373

Have you tried it with the bulbs removed? You must have circuits crossing somewhere. Most likely the rear bulb sockets. If you remove bulbs and the problem goes away then that gives you something to work with.
Remove all rear bulbs and hit the brake. Do you still have the problem, etc.
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

TJ Hopland

Any signs that there was ever a trailer hitch installed?   Trailer light connector?   Look around the rear for any signs that the harness has been messed with.  Where trailer lights were spliced in is one of the best places to find issues.

StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

grantatx

Jeff, you're 100% correct, it was one of the bulb sockets! Thank you!

Now the question is, how do I fix it? Are they a commonly available part? Guess I'll consult Google :-)

chrisntam

1970 Deville Convertible 
Dallas, Texas

grantatx

Update: I got a replacement socket from O'Reilly, cut the old one off and tested with the new socket. The problem was still there! Believe it or not, it was the bulb that was causing the problem. A new $2 1157 bulb fixed it.