1990 Deville third brake light
 

The third brake light behind the rear windshield (high level brake light) isn't working. So I took the cover off and all 3 bulbs were burned out. So I thought no big deal, so I put in 3 new 1141 bulbs (thats what the old ones were) and nothing. so I stuck a volt meter on the plugs and hit the brake peddle and got more nothin. But the 2 main brake lights work.

I got the wiring diagram from alldata:
http://img220.imageshack.us/img220/7...2971ew7.th.gif

The high level stop light is turned on by the brake light switch. The switch seems to have two contacts - one that goes to the rear brake lights and on that goes to the HLSL. So did one contact burn out/stick/get dirty? I'm I on the right track that I probably need a new brake switch?

And most importantly

Anyone know where it is/how to get to it?

Thanks.

RE: 1990 Deville third brake light
 

Did you put a volt meter on the switch? torule outthe switch function. If no voltage at the HLSL portion, replace switch, if power, look for an open connection somewhere.

RE: 1990 Deville third brake light
 

I haven't tested the switch yet. I took lose a cover under the dash by the brake peddle looking for the switch. I ran into some CAUTION AIR BAG stickers on wires. So I disconnected the ground on the battery and am waiting a while to disarm the air bag system. Don't want to unplug or bump something just right and set the air bags off. That would really piss me off. lol.

If anyone knows what the switch looks like or anything like that, it would be helpful.

If I can I will take a picture or two if/when I find it.

thanks.

RE: 1990 Deville third brake light
 

I found the switch. Just follow the brake peddle, which is easier said than done. You have to stand on top of your head (literally) in order to see it. They best way I found was to lay across the passenger front seat so that your head is in the drivers seat. Then slide down at an angle with your head agaist the floor. Your head and shoulder keep you from sliding anyfurther and frees both of your hands.

Here is a picture of what it looks like.

http://img87.imageshack.us/img87/465...0913bw0.th.jpg

My switch didn't have two nuts to hold it in place like normal. Instead it is just crammed into a metal ring that pinches the threads. So once I had the two plugs undone, I just twisted and pulled at the same time and it popped out.

The black cover pops off and gives you access to the contacts. Hopfully I can locate a new one. If not you could clean it and see if it makes another round.

RE: 1990 Deville third brake light
 

Great info and photo. Thanks for taking the time to post. It will help others in the futrue I'm sure.

G.A.R.Y.

RE: 1990 Deville third brake light
 

Thanks. I have found so much useful info on the net (mostly forums) for a huge variety things, it's not even funny. So if I can, I try and give a little back.


So, I went to autozone and they had a new switch for 7 bucks. I plugged it in, hooked up the battery, and hit the plunger with my finger and both back stop lights light up and the high level light still didn't light up!

For 7 bucks I'm gonna go ahead and put the new switch in tomorrow and that will be one less thing to worry about.

That really sucks... the other thing left is the wiring itself and grounds - oh joy. :(

RE: 1990 Deville third brake light
 

Well I dove in on the wiring today.

This is a ground wire diagram (turns out I didn't need it for the HLSL though):
http://img67.imageshack.us/img67/488...3058rt1.th.gif

What is interesting in the HLSL and Fuel Tank Units grounds are interconnected (I am also having probs with a new fuel pump) I get to that later though.

To see if the hot wire from the brake switch to the lights was good I used a meter to do a continuity test -- which it failed. So, I have a break in the power wire some where between the swith and the stop light.

Wiring hunting time...

So the first thing to do is to take the back seat out. For the first time that is something that sounds harder than it really is. To remove the seat bottom (the part you sit on) just hit each side of the front of the seat firmly with your hand which pops it lose. Then lift the front up and pull out and then you can take it out of the way. Then get you shop vac ready because after 18 years of stuff have made its way under it.... Being a Cadillac I found a 1976 dollar coin - no pennies here. lol.

Ok next is the back rest which comes out in two pieces and takes only four bolts.
The first two are where the seat belts are bolted to the floor pan. As you can see there is a metal loop that goes around under the bolt:
http://img67.imageshack.us/img67/9560/P1010927.th.jpg

With the bottom lose there are two more bolts under the shoulder belt cover. The cover comes off with one screw:
http://img67.imageshack.us/img67/6581/P1010929.th.jpg
The plastic on the covers were pretty brittle so take it easy.

Here you can see the bolt after the cover is removed:
http://img67.imageshack.us/img67/6035/P1010931.th.jpg

With the top two bolts out, the head rest can be pulled off (this MUST be done first)
I forgot to take a picture, but here is how the head rest look seperated from the back rest:
http://img67.imageshack.us/img67/6356/P1010941.th.jpg

Then you lift up and pull out to remove the back rest. And then after vacuuming some more you have this:
http://img67.imageshack.us/img67/2286/P1010933.th.jpg

To lift up the carpeted shelf thing, you slip the seat belts through the slit that they have:
http://img67.imageshack.us/img67/4196/P1010937.th.jpg

Then I was able to lift it up enough to see the wires that went to the HLSL and here is what I found:
http://img67.imageshack.us/img67/1593/P1010942.th.jpg

Both the ground and the hot wire were broken. Not to sure what happened. But I fixed them up with some scrap wire:
http://img67.imageshack.us/img67/4605/P1010945.th.jpg

Then hooked the ground back up on the battery. And drum roll please.......
http://img67.imageshack.us/img67/4842/P1010948.th.jpg

They worked! To finish up I wiggled each connection to make sure the lights didn't flicker ensuring I had a good connection. Then wrapped them with electral tape and tucked it back where it goes.


What does this have to do with the fuel pump? Well a bundle of wires seems to go right on top of the fuel tank. So I'm gonna leave the seats out incase I need to get to it. It goes under this rusted panel:
http://img67.imageshack.us/img67/8311/P1010949.th.jpg

Anyway it has a new fuel pump that went fine for a tank of fuel and then went toes up. Then came on for about two mins again and died again. Sounds electrical to me... I might have to make a fuel pump thread.

RE: 1990 Deville third brake light
 

I can't tell you how many times we have been asked how do you remove the back seat? Your step by step with photos will enable the most inept backyard do it yourselfer to accomplish this.. Again job well done. Interested in hearing the resolution to the fuel pump problem. I have in the past purchased a bad fuel pump and installed. What a pain, hope it's just a connection for you to find. Good luck.