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Discussion Starter #1 (Edited)
For the last few weeks I've been chasing a pesky and intermittent "Brake" and "Stop" warning light issue on my '91 164S. It's a potential serious issue since when it would come on none of the brake lights worked. At first I didn't realize this, thinking it was just a bad bulb, or one going bad creating incorrect resistance, thus flagging. However, all bulbs and sockets appear good and corrosion free.

A few days ago, the warning lights came on steady, which gave me the chance to better diagnose the fault. Given that none of the lights were working, I figured it was either the Rear Lamps Control Unit (N44) or Alfa Romeo Control Unit (N22), or the wiring/connectors to them.

Also, the RLCU and the ARCU are under the dash on the right side in close proximity to the evaporator unit, increasing the possibility of moisture induced corrosion. Both are easy to loosen and remove, the RLCU attached to the courtesy light bracket and having two phillips head screws, and the ARCU having two 8mm nuts. Remove the RLCU first, then the ARCU. The ARCU is a bit of an enigma as it has many functions, some not very well described in the tech literature.

Regardless, after loosening the boxes and moving the wires a bit on the "A" connector (the one that has the RLCU connections), I noticed the dash warning lights went out and the brake lights worked again. I removed the ARCU, opened it, and looked at the circuit boards. All solder connections were very well soldered with no cold joints. However, I did notice (see pic below) that the male connector pins seemed to be slightly corroded with a whitish coating. I cleaned them up as best I could. The wiring harness connectors appeared good with no damaged wires. All connections were cleaned with electrical cleaner spray. If you're having other funky intermittent problems, like the interior courtesy lights not coming on, not going off, etc, it's probably bad/corroded connections at the ARCU.

So far so good and ops normal, but time will tell.

Since the Electrical Service Manual doesn't have a good depiction of the ARCU or RLCU pin-out, I did the ones shown below. Note that the green connectors attached to the yellow base connectors and vice-versa. However, they are all different sizes, so you can't get it wrong when you go to connect everything back up. I hope this helps someone else diagnose a irritating intermittent fault like I experienced.

There's a PDF download of these pin-out pictures at the bottom of the second post.
 

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Nice!! Glad someone else takes stuff apart!!! Thanx, it just might come on handy here. ciao chris
 

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Very well done indeed.
Maybe it applies to a 24v as well.
I have gone though all connection and cleaned them, would like to check these as well
 

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Thanks for the information John; Good Job! I did not realize that when the dash warning lights came on the brake lights were out. I have noticed the warning lights coming on several times. While under warranty, 20 years ago, the dealership (PSA) installed new tail light bulbs to correct this issue.

You mentioned the connector; I suspect you forgot the picture (or I missed it): I did notice (see pic below) that the male connector pins seemed to be slightly corroded with a whitish coating. I would lightly coat this connector after cleaning with dielectric grease or Vaseline to prevent additional corrosion.

I wish this issue would explain why the antenna on the "S" will go up and down, at the expense of a fuse each time and why the sunroof will open only 5% of the time and the top row of center dash 'back ground' lights are out at night but perhaps I ask too much.

Yesterday, I added 'Alfisto Steve's' Radiator Bypass to the 1992 'S' with a 1" PEX ball valve from Home Depot and am feeling much cooler already even with no working A/C! Perhaps today will be a good day to check out the electric control modules on the 'S'

Much appreciated,
Mark
 

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Very well done indeed.
Maybe it applies to a 24v as well.
I have gone though all connection and cleaned them, would like to check these as well
The 94-95 164 models do not have this N22 ARCU system.
 

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I wish this issue would explain why the antenna on the "S" will go up and down, at the expense of a fuse each time and why the sunroof will open only 5% of the time and the top row of center dash 'back ground' lights are out at night but perhaps I ask too much.

Much appreciated,
Mark
Which fuse are you blowing 10A F5 fuse in G2 small aux fuse box?
 

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Discussion Starter #8 (Edited)
I did not realize that when the dash warning lights came on the brake lights were out. I have noticed the warning lights coming on several times. While under warranty, 20 years ago, the dealership (PSA) installed new tail light bulbs to correct this issue.
The dash lights can indicate only one or more lights out or all. In my case it's not a bulb, but one of the main feed wires from the ARCU to the RLCU, which affects all the lights . . . . a good reason to stop and investigate the actual status of your stop lights. If they're all out and you get smacked in the rear, issues could erupt.
 

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When my 91S started having those two particular lights do their intermittent thing, We checked, and the brake lights don't go out on my car, but those warning lights do if I just touch the brake pedal.

However, thanks for the warning, will check again, and probably clean all those connections you show in your great posting.
 

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When mine was doing that I found the 2 indicator lights came on when the brake pedal was depressed, but the brakes lights didn't. When a bulb is burnt out, the indicator lights are on, but go out when the brake lights come on.
 

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When the lights came on in my 91S when I pushed the brake pedal, as compared to going off when I touched the pedal, found that the fluid was low. Refilled, and all was fine.
 

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Which fuse are you blowing 10A F5 fuse in G2 small aux fuse box?
Yes, however I replaced the blown fuse (20A whoops) with a 10A in F5 aux fuse box and removed relays D,E,F (mirrors, sun roof & front windows) in the process the fuse panel screw came out and the fuse panel came down. I reinserted the relays and screwed the fuse panel screw back in place and when the power was applied (key turned) the antenna worked without blowing the fuse! Also, the front and rear courtesy, door bottom and back (red lenses) worked as well. Its been a few years since all these lights worked and I wonder if there was a short in the wires behind the fuse panel that got separated when the fuse panel came down?

Unfortunately the sunroof is still temperamental; when I hear it rattling as I go down a rough road, I know that it will open again but most likely not until then (I just noticed the seat heaters are on the same fuse; not that I need them now but they don't work either). Also, the outside mirrors will still not power adjust but that's not a big deal since its only a one driver car.

Apologies to Roadtrip for hi-jacking, last week my "pesky and intermittent "Brake" and "Stop" warning lights" flashed on as I watched a car rapidly approaching in the rearview mirror around a turn; I quickly pumped the brakes, clearing the warning lights and showing him my brake lights. Thank for the warning!
Mark
 

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My interior lights decided to not shut off today after turning the ignition off and I heard from around the glove box area what sounded like the old key buzzers on my 74 spider, it wouldn't stop buzzing till I turned the ignition back on so I hurried up and disconnected the battery. Now after changing out the battery with a fully charged one (thinking that was the problem) the buzzing stopped (which I'm assuming was coming out of a relay somewhere) but now the interior lights stay on. When I have the ignition on and all the doors closed the driver front and passenger rear door lights in the gauge cluster are lit. I changed out the N22 control unit and I have the same problem.
I can't see how it can be possible for both door switches to go bad at the exact time. Its got to be a relay somewhere, if someone can advise me as to what to look for that would be greatly appreciated.
 

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How about the switches on the sunroof control panel are they on or the switches in the C-pillar rear lights?

Are you sure you changed N22 ARCU unit under and behind glove box or did you change N44 rear lamp control unit attached to footwell lamp?

Buzzing was probably from N22 unit which is mounted on two 6mm studs with 10mm nuts and has about five connectors.

I26 relay for system in main fuse box top right relay. Pull it and see if lights go out.
 

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Yes I changed the n22 unit that has the 5 multi pin connectors on it. Puled the I26 relay and all the interior lights are still on, upon pulling it out I can here that relay switching. They eventually go out after about 5 min but then they don't come back on till I disconnect and reconnect the battery.
 

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Troubleshooting 164 interior lights staying on issue

Yes I changed the n22 unit that has the 5 multi pin connectors on it. Puled the I26 relay and all the interior lights are still on, upon pulling it out I can here that relay switching. They eventually go out after about 5 min but then they don't come back on till I disconnect and reconnect the battery.
I take it you put the I26 relay back in, too? did you do that before or after reconnecting the battery?

N22 does the timer thing and as far as I know it is the only device in system to do it.

Do sunroof panel lights and C-pillar lights both come on?
 

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I took the driver side lower door panel off to get to the connector for the switch in the door latch, I tested the continuity of the switch and the switch is stuck open, its about 28 degrees this morning, so I think whats going on is the oil that is in the latch assembly has gotten so sticky over the years that the slider that goes between the magnetic proximity switch and the stationary magnet is stuck, after heating the latch up with a hair dryer it started working again. I played around with the other door latch with my fingers latching and unlatching it several times and that one started working too. Now the lights turn off as they should, although that doesn't explain why it was acting up yesterday when it was 40 or why or what relay was buzzing uncontrollably? Im thinking it was the long black relay with a 10 amp fuse attached to it that is behind the passenger access panel under the dash vent? What does that relay control?
 

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I57 ABS relay with free 10A fuse holder G125 nearby.
 

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I had this problem occurring from time to time until the BRAKE and STOP lights stayed on when brake pedal was pressed. I'd like to add a note to this thread that it may also be the relay (grey? 20A) behind the false firewall. I don't know where or how it should be attached but mine was just laying there so that water could get into the relay and cause the malfunction.
 
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