1987 Toyota Camry -BRAKE (STOP) LIGHTS DO NOT LIGHT

[josiah]

I appreciate the reply.
Yes, I am talking about the plastic connector which the brake light switch plugs into. The connector has 4 slots which match with the switch 4 terminals.
Regarding the brake light switch only one terminal had corrosion and that was terminal#3 (the other terminals looked fine with no noticeable corrosion). So I removed the switch and sanded the corrosion off with extra-fine sandpaper. After removing the corrosion the switch passed the resistance test.
This is an aggravating job because of the cramped space which only allows working with one hand only.
Do you know how I can remove the connector+wires? If I could remove it cleaning it should be easy.
Thanks.

 

[josiah]

Thanks for reply.
I am talking about the connector which the brake light switch plugs into. The switch has 4 terminals which match with 4 slots in the connector.
Please tell me how I can remove connector+wires. If I can remove it cleaning it should be easy.
Thanks.

 

[josiah]

How do i remove the connector?
Cleaning where it is would be difficult.
If I could remove it cleaning it should be easy.
Thanks.

 

[grcauto]

The connector isn't the maltiplug. Not sure how you can get at it. On the switch the #3 goes to the computer and is critical. That needs to be clean.

 

[josiah]

grcauto,
Please pardon delay in responding; busy with home appliance repair and replacement.
Not sure you are talking about the same switch I am dealing with. I am talking about the 4 slot connector which connects to the 4 terminals of the brake light switch. I assumed the sole reason for the connector was to supply power to the switch. Not aware that the connector had any impact on the computer.
Thanks.

 

[billr]

That (4-pin) switch does not power-on the brake lights, the PCM turns on the lights. The pedal switch sends a signal to the PCM so the PCM can determine if the brake lights are to be turned on. Grc is not understanding that you have found corrosion on the contacts of that 4-pin connector right at the brake pedal.

Power for that switch comes from the PCM. I was trying to get you to check that power by measuring voltage at pins 1 and 3 of the switch cable. If you get no joy cleaning those connector contacts, then we will have to get back to how you go about checking voltages with a meter.

 

[josiah]

billr, grcauto, Jack C, Paulo57509

In your prior reply you said-> "What voltage do you have, referenced to ground, on pin 3 and pin 1 of the brake-light switch harness? Check this with KOEO and with the harness connected to the switch and disconnected, both ways. Did you try connecting the switch to the harness, unmounted?
GRC, do you have more of the wiring diagram? I would like to follow that circuit to the PCM and then on to the brake lights themselves."

My problem:
(1) For testing all I have is a volt-ohm tester. I don't know what is a (1) KOEM or (2) PCM? I never heard of either until now.
(2) I know what a brake light switch is but I don't know for sure what is the brake-light switch harness?
(3) I only ASSUMED (based only on a test of switch) the connector might be the problem only because I saw corrosion on the connector slot and the switch terminal.


Paulo57509, you mentioned the possible problem could be a loose wire in the trunk. I know that prior to the problem I did clean out the trunk. So I plan to take a good look for a possible loose wire.

Additional info would be appreciated.
Thanks.

 

[billr]

Do you know how to use the voltmeter to measure DC volts? Is the meter a modern digital unit, or a very old analog one? I'm trying to ensure your meter has input impedance high enough for doing the checks I would like you to do. If you have specs for the meter, or know the input impedance, then let me know what it is. If you do know how to use the meter, then I am asking you to connect one lead to ground (engine, battery, chassis... any will do) and connect the other lead to pin 1 of that switch circuit and read DC voltage. Repeat on pin 3 to ground

A "harness" or "loom" is the common name for the wiring bundle between two (or more) components. In this case I am talking about the group of four wires that connects to that brake switch.

"PCM" is the acronym for a Powertrain Control Module; the computer that controls the engine, transmission, traction control, ABS, etc.

"KOEO" is Key On, Engine Off. That means the ignition switch has been moved to the "run" position so all circuits are powered up, all dash light should come on, but the engine has not been cranked to start it. The engine is not running.

 

[josiah]

Billr,
Yes, I have measured my battery DC volts before.
Yes, meter is Sears Craftsman Digital Multimeter 82339. Input Impedance 10M OHM (VDC and VAC)<-(found in owner's manual).
Is meter adequate?
Above you said "connect one lead to ground (engine, battery, chassis... any will do) and connect the other lead to pin 1 of that switch circuit".
So do I (1) ground the negative test lead and (2) PARTIALLY plug brake light switch into the connector leaving a small gap to allow the positive test lead to be inserted in between and (3) do this for #1 and #3 terminals?
I appreciate the complete explanations for harness, PCM and KOEO above. I will note this so that next time I will know what you are talking about and won't be so confused.
Thanks.

 

[paulo57509]

billr, grcauto, Jack C, Paulo57509

In your prior reply you said-> "What voltage do you have, referenced to ground, on pin 3 and pin 1 of the brake-light switch harness? Check this with KOEO and with the harness connected to the switch and disconnected, both ways. Did you try connecting the switch to the harness, unmounted?
GRC, do you have more of the wiring diagram? I would like to follow that circuit to the PCM and then on to the brake lights themselves."

My problem:
(1) For testing all I have is a volt-ohm tester. I don't know what is a (1) KOEM or (2) PCM? I never heard of either until now.
(2) I know what a brake light switch is but I don't know for sure what is the brake-light switch harness?
(3) I only ASSUMED (based only on a test of switch) the connector might be the problem only because I saw corrosion on the connector slot and the switch terminal.


Paulo57509, you mentioned the possible problem could be a loose wire in the trunk. I know that prior to the problem I did clean out the trunk. So I plan to take a good look for a possible loose wire.

Additional info would be appreciated.
Thanks.

FWIW...

I had an '87 Camry years ago. It also had a brake light problem. IIRC, no brake lights and no brake lamp failure warning light.

There is a plastic junction box/block inside the trunk (either on the back wall of the trunk or lid) where I found a loose ring terminal under a screw. Tightened it and issue went away. The screw threads into plastic so don't over tighten.

I recently pitched my factory Toyota '87 Camry service manual. Unfortunate circumstance.

Again as I recollect, the junction box is either on the underside of the trunk lid (behind the lights) or on the back wall of the trunk (behind the lights). It's maybe a 2" or 3" square box. I think the box has a pry-off cover so it's unlikely that something knocked something out of place. I was surprised to find that loose ring terminal. My guess thermal expansion/contraction?

 

[billr]

"So do I (1) ground the negative test lead and (2) PARTIALLY plug brake light switch into the connector leaving a small gap to allow the positive test lead to be inserted in between and (3) do this for #1 and #3 terminals? "

Yes, that is essentially what I am asking you to do. However, when making readings with the harness connected it will be better to have the connector fully mated (no gap) and "back-probe" into the wire-side of the harness connector. You may be able to even see the metal contacts in the housing, from that wire-side, and get the meter probe in to reach them. If the contacts are too deep to reach, or hidden by a rubber seal around the wire, then try slipping in a thin probe "extension", like a (metal) paper-clip or sewing needle. Or, the sewing needle can be used to pierce the wire insulation so that it contacts the wire itself.

Now for the tedious/confusing part. I am asking for six different voltage readings, all with KOEO:

1) Pin 1 to ground, with harness connected to switch and switch contacts open
2) Pin 1 to ground, with harness connected to switch and switch contacts closed
3) Pin 1 of harness, with harness disconnected from switch (this can be easily done without the "back-probing")

Then repeat above for Pin 3 to ground.

I have to warn you that when I get the results I will probably not know yet what the problem is or how to fix it. I am asking for these readings as data for "reverse engineering" the system to try figuring out how to definitively trouble-shoot it. It is also likely that I will have to have you move on to other connectors, like the one already mentioned by <grcauto>. That back-probing technique will probably be used many times...

Certainly check connections in that junction box, as mentioned above. It would be sad if I led you through a long trouble-shooting process that ended at simply a loose terminal in that box!

 

[grcauto]

You can't back probe it? If not use piercing probes.

 

[josiah]

billr , grcauto and paulo 57509,

1) I want to clarify what was said above-> Billr on Tuesday 10/5-> "Grc is not understanding that you have found corrosion on the contacts of that 4-pin connector right at the brake pedal". Clarification->I found corrosion on the brake light switch terminal#3 (remaining 3 terminals looked fine). Also the connector (which connects to switch) also had corrosion on the matching #3 slot.
2) Paulo 57509-> Will take another good look in the trunk ASAP. I hope it's that simple. As I said previously I was cleaning out the truck shortly (a week or two) before the problem occurred.
3) Billr->Above you informed me to check the impedance for terminal/slot#1 and #3. Where should I set my meter? My multimeter has V DC scale of 200m (lowest) to 1000 (highest) and ohms scale of 200(lowest) up to 200M.
4) Billr->to do the impedance test could i simply instead insert a wire (or paper clip) in the connector slot#1 take my reading and do the same for #3?
If I insert the switch completely in to the connector testing would be difficult. Honestly I don't want to insert that switch completely into the connector because disconnecting them can be difficult. I only want to completely connect them when I know the job is done.
5) Billr->I really do not understand "impedance". When I take the readings what will I see? I have done resistance test before for example testing the brake switch where you are looking for no resistance. However impedance I don't completely understand.
6) Billr->regarding my multimeter, only jacks (1)v.ohm.cap and (2)COM are available. Jacks (1) 10A and (2) mA are not available(blocked off).

Please don't concern yourself with solving the problem. You trying to help me is very much appreciated.
Thanks.

 

[billr]

I am not asking for you to check impedance related to pins 1 & 2; I am asking for voltage readings, so use the "VDC" range.

Roughly speaking, impedance is much the same as resistance; as is "reactance". Resistance is applicable to both AC and DC circuits, but reactance applies mainly to AC circuits. Impedance is simply the combined over-all effect of resistance added to reactance. Clear as mud?

How much your meter loads a circuit, and can affect the reading accuracy, is determined by the resistance/impedance of the meter circuitry connected to the probe leads. Since most meters are AC/DC, impedance is usually what is specified; but on a DC range it will really be just resistance alone.

 

[josiah]

billr,
I appreciate the explanation; I will read it a few more times, perhaps it will sink in.
I plan to take the readings at the connector because plugging in the switch to the connector and afterwards taking the readings may be a problem.
Paulo57509,
I took a good look in the trunk and I saw no loose wire. I plan to take another look tomorrow or Monday.

Thanks.