stabben

Hello!

I was hoping for some verification of, or insight into, my electrical problem (I have done a forum search already, but found no conclusive info...). Here's all the relevant info to start with:

1991 convertible, 95000 miles, standard shift.
Stock alarm system, door chime, key illumination light stopped working cold. NO response or activity from either of the systems. Checked the room fuse and it's fine. Sounds like a CPU solder problem, right? But, today I also noticed the high beam doesn't come on either, and I don't think the lights are governed by the CPU. I replaced the headlight switch not even a year ago with a new Mazda unit, so should be fine. All other lights work fine, blinkers etc. Even the fog lights. And all other systems are working normally as well, including the courtesy lights.

Is it really the CPU? Any other ideas?

Thanks for your input!
Joakim

Oh, yes, the key/alarm/lights on buzzers don't work either suddenly.

Icemark

Key lumination is probably a burnt bulb, unless both the door key and the ignition key lights are out. Then it could be related to the CPU.

if the interior lights are working it rules out the fuse. so for the warning it does sound like the CPU needs resoldering.

When you replaced the headlight switch did you replace the light harness as well??? it is generally recommended. and I am assuming you checked the fuse before posting. Well the next step would be to check and see if you have ground coming out of the switch on the wht/blu wire when the head light switch is on.

stabben

Icemark,

Thanks for your input! I did check the fuse before posting.
When the headlight switch was replaced last year I was dumb(er) and green(er) as a rex owner and the harness never was replaced even though I thought I should be. The mechanic disagreed and I let it go at that...

The door key light has never worked - burned bulb. What I meant was the buzzer when you leave the key in, and the key light on the steering column stopped working as well. I should have been more clear here.
Sounds like you think these are two separate, unrelated issues, then? CPU soldering AND light wiring harness?

Any opinions to the contrary, or should I run with what Icemark says?

Thanks all!

Aaron Cake

iTrader: (1)

Often the headlight harness will burn, which will cause a high resistance connection at the switch. This will destroy the connector at the new switch.

jacobcartmill

iTrader: (6)

i resoldered my CPU and it corrected alot of those little problems. also, my bright lights werent coming on after replacing the switch for the headlights. i tracked down the power that goes to the bulbs and gave each one a little tug (one for each light assembly of course) and the brights suddenly came on. when i resoldered the cpu, all of my buzzers and security light and stuff worked for a few minutes, then they went out again (i guess i need to resolder it again or get a new cpu)

Aaron Cake

iTrader: (1)

Resoldering must be done correctly, or the joints are worse than the original Mazda joints....Read these:

- http://www.aaroncake.net/electronics/desolder.htm
- http://www.aaroncake.net/electronics/solder.htm

Icemark

yep as Aaron mentions, when re-soldering it's not good enough just to heat and re-flow the old solder. You must remove the old and flow in new.

As far as the door key light and the ignition key light, they actually use the same driver in the CPU, so if one is working, they both should. the fact that the door one died first (not unusual being the door gets slammed and that is very hard on incandescent bulbs) still would point me to bad bulbs.

The buzzer in the CPU also tends to go out with age and dampness. I almost always replace the buzzer when I rebuild a CPU. The easy check is to see if you have a buzzer when the door is open and the parking/headlights are on. If its not working then, chances are the buzzer needs resoldering or replacing.

stabben

Great inputs!! Thanks!
I guess I'll look into the soldering bit first and go from there. Do the harness second.

Thanks Aaron for the links.

Joakim

stabben

Icemark,

Thanks for your input! I did check the fuse before posting.
When the headlight switch was replaced last year I was dumb(er) and green(er) as a rex owner and the harness never was replaced even though I thought I should be. The mechanic disagreed and I let it go at that...

The door key light has never worked - burned bulb. What I meant was the buzzer when you leave the key in, and the key light on the steering column stopped working as well. I should have been more clear here.
Sounds like you think these are two separate, unrelated issues, then? CPU soldering AND light wiring harness?

Any opinions to the contrary, or should I run with what Icemark says?

Thanks all!


EDIT: Please remove this last post, I goofed hitting the re-load button... sorry! Still a newbie!

writersblock

I had a similar problem I solved over the weekend. The bright lights indeed do run through the CPU. A white with blue stripe wire runs from the combination switch to the CPU. A white only wire leaves the CPU and connects to the trigger on the dimmer relay. I can only surmise that the switch sends a momentary signal to the CPU that then sends a constant signal to the dimmer relay, thus turning on the brights. NOTE: The flash to pass function is different and uses the low beams, so the FTP may work, but the brights won't.

None of the burglar alarm stuff worked either.

With all of that said, here's how to fix it. You can go the resolder route, which is cheaper, but if you're not skilled in soldering, you might want to avoid that. You can order a new board for the CPU from Mazda. According to my parts fiche, it is FC66-67-564 (with air bag). Mazdatrix sells it for $79. I have actually ordered the part, so I'll share my experiences when it comes in.

Just so you know, we came to this conclusion after checking literally every other piece of the system. It took us nearly four hours of testing, but we got there!

Writersblock

jacobcartmill

iTrader: (6)

this thread is over 3 years old

Icemark

Highbeam control in the CPU is only on the FC66 CPU found in the convertibles with SRS. Not in any other model.

The Circuit is indeed a electric latching circuit in the CPU, much like the high beam /Turn signal switch is in the S4 models.

writersblock

I'm curious then if I actually ordered the right part. Did I? I assumed that only a handful of coupes had SRS, and all of the convertibles had it in 1991.

Writersblock