92 740T brake lights hate me Topic is solved

Guest · Post by **Guest** » 05 Apr 2003, 20:49

No brake lights. Tail/fog/reverse/turn signal lights work, and replaced stop light switch. Bulbs and fuse are fine. Can the bulb failure sensor go bad in certain parts and be OK in others? Sensor light not on-nto sure what the dealio. Any ehlp would be appreciated, as I have no desire to be rear-ended by some Pontiac. This would total his car and do at least 75$ worth of damage to my bumper.

Volvord · Post by **Volvord** » 05 Apr 2003, 21:39

It sounds like you may have a bad ground. Use a test light and check for power and you will also be able to test for a bad ground.

Volvord 784VC
http://www.telusplanet.net/public/gilesij/Volvord/

Guest · Post by **Guest** » 05 Apr 2003, 22:54

Thanks. Can you be more specific? I looked at the wiring diagrams in Chiltons, but there isn't much to go on there. Where do I test? What equipment? Any special multimeters? I was at Sears today and saw some, but not sure what I'm looking at or how to use it.

Volvord · Post by **Volvord** » 06 Apr 2003, 16:01

Using a simple 12V test light or any multimeter turn the lights on and probe the power wires entering the bulb sockets, the test light should come on or the meter will register 12V, if it does not then you problem is the feed circuit. If the test light does go on you have power, now probe the ground wire, there should not be any power here, if there is the ground is faulty. Trace the ground wire to where it gounds to the body, usually a small screw or bolt. Clean this area well and tighten, retest.

If you do not have any power to the rear lights start with the fuses, check these with a test light, with the ignition on and the lights on, there should be power on BOTH sides of each lighing fuse, if there is only power on one side then the fuse has blown.

Don't forget to check the bulbs, the rear lens units of these cars are prone to fillinmg with water which will cause the bulbs to fail, if you see signs of water in the lens drill a small 1/8" hole in the bottom corner of each lens to act as a drain.

Volvord 784VC
http://www.telusplanet.net/public/gilesij/Volvord/

Usually light problems like yours are quite simple

Guest · Post by **Guest** » 07 Apr 2003, 14:43

Thanks alot. I'm working on it, and will pick up the multimeter poste haste. However, I think the light problem was the bulb sensor now. The sensor isn't operable (I removed a bulb-it didn't go on). I'm replacing that part (which needs to be done anyway), and will also test the grounds at the rear lamps.

Off topic: I found the problem with my boost gauge (dead). There was a crack in the hose right where the hose enters the engine compartment.

Guest · Post by **Guest** » 21 Apr 2003, 13:28

Hey volvord-do you by chance know the route the brake light wires follow from the switch to the lamps? I've replaced the bulb failure sensor with a new (used) part, which did not cure my problem with the lights.

I have also inspected the grounds for the tail lights and the high-mount brake light in the tailgate panel, and am testing the grounds tonight with a meter. I know the switch works, because it trips the shift lock release, and you can hear it operating. I also know the fuse seat is operational, because I burned it out replacing the sensor, and the shift lock wouldn't release without a new fuse in place. Now the fuse is fine, as I have replaced that as well.

I'd like to know how the wires get to the rear so I don't have to play "tear apart and hunt them down". I'm thinking that there may be a damaged power or ground line between the console and the tail.

As a final, I'm also replacing the bulbs in the tail lights-you never know.

BTW, sweet conversion. After looking at your site, I found myself wandering onto Ebay, clicking 302's, speaking softly to myself about what additional tools I might find useful, were I to undertake such a project (and the divorce which would inevitably follow!)....

have you considered turbocharging that beast?

Volvord · Post by **Volvord** » 21 Apr 2003, 19:04

The wiring harness passes through the inside of the car under the carpets, but it would be very unusual for the problem to be in the wiring itself. It is not unusual for the bulbs to be burned out so do replace those first, use the meter to check for power at the sockets, I would also check the brake light switch with the meter to ensure it is working. If you do have power through the switch and no power at the rear sockets then check the grounds, if they are OK then start with the wiring harness in the truck, this one is damaged the easiest.

Thank you for your comments about my car, although I have thought about it I really have no desire to turbo the V8 engine. It is very fast the way it is and with the new engine I am building will produce around 450 HP. Any more than that and onther components start breaking too easily.

Hope the info helps with your problem.

Guest · Post by **Guest** » 22 Apr 2003, 12:56

No trunk-it's a wagon. There's power at the sockets (because the tail lights work, and these are the same as the brake lights, but the brakes make them brighter). I tested the grounds with the light, and the light didn't light up. Did light up when applied to the power points at the sockets. Sensor lights up when a bulb is removed. Fuse good. Switch power good (because it releases the shift lock-or is there a separate power supply for that?).

Volvord · Post by **Volvord** » 22 Apr 2003, 13:24

The brake/tail light bulbs (bulb #1157) have two filiments inside them, they are really two bulbs in one that work on two seperate circuits. Just because the tail lights work does not mean the brake lights will work or are recieving power, also one of the filiments can burn out and the other work fine. Test the brake lights as a seperate circuit.

Guest · Post by **Guest** » 23 Apr 2003, 14:26

Yep-the plastic bulb base has different prongs on it for the tail and brake light circuits. That's why the bulb has retention pins at different positions on opposite sides of the bulb shaft, and also why the bulb base has three tines on it, one of which is different in size than the other two (so you can only put it in one way, maintaining integrity between the bulbs of both sides and always using the right filament for the right function of the bulb).

Still doesn't work. I'm going to get a soldering iron and tear into the bulb failure sensor per brickboard's directions. I know that terminal 56 stuff is for the low beams. Do you know what the other terminals are for, number wise? The sensor controls low beams, tail and brake. I think I'll start with redoing the connections on the top plate of the sensor, and see if that works. May also try to isolate the brake connections by removing the sensor that's in there now and testing the base for current. Probably a good idea anyway.