My 93 940T Wagon has been sitting for awhile needing new exhaust manifold gaskets. Necessity caused me to get it back on the road where I discovered my center brake light, backup lights and rear blinkers were all that are functioning.

I checked fuses with no problem found and assumed that the brake pedal switch was good because of the functional center light. I then pulled the bulb failure relay where I found an open circuit between pins 54 and 54r.

Thanks to the help of Art Benstein I was able to take the relay apart without destroying it and today I reflowed the solder to 54r and got the circuit repaired.

But once installed I still don't have lower brake lights or rear running lights. Any suggestions on where to look next or what I should check again? Thanks,AG

Thank you BB and Spook. I will follow both of your suggestions.

About all we can safely conclude from your statements is that
a) the brake light switch at the pedal is working normally
b) one of the three brake light circuits inside the bulb sensor is okay, pin 54 (input from brake light switch) to pin S (output to 3rd brake light)
c) the 3rd brake light bulb is okay
d) the chassis ground at the 3rd brake light is okay.

As much as your re-soldering restored continuity in the bulb sensor between pin 54 (input from brake light switch) to 54R (output to right brake light), that doesn't explain loss of the left brake light lamp (on 54L).

First off, hope you didn't neglect the obvious and verified bulb integrity. Remove the left and right rear bulb holders, visually inspect for broken or loose filaments and additionally use a meter to check for continuity between each of the two contact points and the bulb base.

Once you've verified bulb integrity, at the tail light assemblies you should then verify with a meter whether voltage is getting to either the left or the right brake light bulb socket when the pedal is depressed.

Failing 12 volts getting to a tail light, the next step is to verify voltage at the bulb sensor pins. To easily do this, make yourself a one foot test lead of copper wire (preferably solid core rather than stranded wire to help prevent accidentally shorting to nearby contacts). Bare about a good 1/2 inch of wire at one end, long enough to be able to wrap a couple of loops around a pin of the bulb sensor. At the other end just bare enough to be able to touch a test lead probe. With your test wire wrapped around pin 54 and re-inserting the bulb sensor in the relay tray, you should be able to verify with a meter getting 12 volts when the brake pedal is depressed (measuring for voltage between the other end of the test lead and a bare chassis ground point, like the lighter socket case). Repeat the test on pin 54R, then on pin 54L. If you see voltage coming out on those pins then the problem is most likely at the tail light assemblies (given that the relay tray socket isn't slightly melted, resulting in poor contact at the sensor pins). Otherwise the problem remains in the bulb sensor. When re-flowing the solder points in the bulb sensor, be extra careful not to create accidental solder bridges between other points.

Oh, and one other thing. You neglected to mention whether you have park tail lights.

--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

DearAVL940T,

Hope you're well and stay so! The first, low-cost option is based on the lower lights in each cluster not working, while everything else (reverse and turn signals) does work.

So, I'd remove both clusters and clean all electrical contacts - on the cluster bodies and on the bulb-holders - with an aerosol corrosion-remover (e.g., Deoxit).

Coat contacts with di-electric grease, and re-assemble. An invisibly-thin layer of corrosion - perhaps only a few molecules thick - can disrupt a circuit. Deoxit will remove that corrosion.

I suggest this approach, because the car has been idled. Corrosion can form quickly, especially if the car lives in a humid area.

Hope this helps.

Yours faithfully,

Spook

assuming the bulb out sensor is ok
start with checking brake lights fuse 4
check for +12vdc at fuse with brake peddle down
meter ground to cigar lighter ground
+12v meter lead to leg on top of fuse check both legs

test your brake switch
+12vdc at left brake light yellow/red wire
+12vdc at right brake light yellow wire

give the grounds at each brake light an eyeball.


if the the brake lights still are kaput reconfirm the you have continuity from the
brake switch common line to bulb out sensor common leg 54S/9 and the other three legs 54L/10 54R/11 S/5 reflow the common leg if all 3 brake lights kaput.
then check continuity common to each leg with your ohmmeter.

it's tough to read this pdf. the numbers are not so clear.

bill