405 STI Electrical Problems Solved
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  1. #1
    Fellow Frogger!
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    405 STI Electrical Problems Solved

    This post is for information - it took me some time to get to the bottom of problem 1 but the solution was simple:

    Problem 1:
    Fault: Poor earthing of rear lamp clusters: In the 405, Peugeot use a galvanised steel base to house all rear lamps - tail, brake, reverse, turn signal, and fog. It appears that a single wiring loom is fed separately (from the dash board area in the car) to each tail lamp cluster. The wiring looms include an earth wire for each cluster with no local connection. Poor earthing can develop on one (or perhaps both) tail light assemblies.

    Problems that result from the poor earth:
    1. Feedback to fog/driving light circuits causing various degrees of illumination of dash LED in rear fog lamp switch - whether fog lamps are on or off. As problem develops, same LED will momentarily flash with reverse lamps/brake lamps/front fog lamps and flashers.
    2. Feedback will/may cause lock out relay for ABS brakes to activate (bringing on warning light in instrument panel). Relay can lock out when reversing (feedback from reverse lamps illuminated in rear lamp clusters), or from switching on fog lamps while driving, and in principle from any action that activates lamps in the rear lamp cluster.

    Solution to Problem:
    Remove rear plastic trim panel in boot to expose main earth point. Run new separate earth wires from this point and earth each rear lamp cluster. I used 2.5 mm2 cable with cable lugs at each end and secured on the tail lamps clusters with a self tapping screw after cleaning back the galvanising. Problem completely eliminated.

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    Comment: In the 405 for the wiring to the rear lamps, Peugeot use the same size wire for each circuit including the main earth return. It seems that a high resistance connection has developed on the earth pin towards the front of the car at a cable connector (under the dash?), probably as result of undersized wiring or most likely an undersized connector. See below.

    Problem 2:
    Operation of heater blower motor is erratic. Motor will not operate smoothly at the correct speed setting from the dash board slide control.

    Cause: High resistance connection on quick connector located between motor and power transistor controller.

    Solution to Problem: Replace faulty quick connector with a heavy duty connector. Note: the blower motor and speed controller (power transistor) are contained as an integral unit. Remove the blower motor to find a blackened quick connect terminal on one cable between on board power transistor and the motor. Remove faulty connector, clean and fit a new heavy duty connector. Problem completely eliminated.

    Denis

    [ 11 February 2002: Message edited by: Denis ]

    [ 12 February 2002: Message edited by: Denis ]</p>

  2. #2
    Tadpole
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    I know this is an old post, but I could do with a bit of help.

    I have a 1993 Phase 2 Mi16 which has just developed the fualt you described as problem 1. I have the same symptoms, ie, fog light led brightening when pressing brake, etc.

    I am going to try your fix for problem 1, but what I want to know is, did your problem cause the interior light to fail to go off when the doors were closed? This problem started on my car at about the same time, and I'm just wondering if it might be mended with the same fix?

  3. #3
    Fellow Frogger!
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    Quote Originally Posted by P Zero
    I know this is an old post, but I could do with a bit of help.

    I have a 1993 Phase 2 Mi16 which has just developed the fualt you described as problem 1. I have the same symptoms, ie, fog light led brightening when pressing brake, etc.

    I am going to try your fix for problem 1, but what I want to know is, did your problem cause the interior light to fail to go off when the doors were closed? -snip-
    Answer -no. The interior light circuit consists of a three way switch in each interior light (activated by rotating the lens). On/Off/Doors. When connected to door mode, the circuit is made through an chassis/earth connecton at each door switch. If the interior lights remain on, the problem could be a faulty door switch or in the contacts of the interior light assembly (or a wiring fault).

    I suggest you remove the door switches one at a time to see if you can isolate the problem - check for a failed switch allowing the connecting wire to touch the chassis permanently - or a wire with insulation missing / cracked allowing a connection. If all are OK, then the problem may be in the interior light itself. I suggest you remove the light and inspect the operation of the switch. Look for bent connectors. These assemblies are quite simple but it would be eary enough to bend a connection causing the light to remain on.

    If the light still remains on, and you have checked all door switches then the problem would be a wiring fault most lilkely between the light and a door switch.

  4. #4
    Tadpole
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    Thanks for the help. I'll have to attempt both these problems at the weekend then. Hopefully I'll be successful with both!

  5. #5
    Tadpole
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    I re-earthed the tail lights at the weekend. Problem solved with regard to the fog light indicator LED. It now does what its supposed to. Thank you very much.

    No luck with the interior light though. I removed all the door switches, and even replaced a couple of ones with corroded screws with ones from the scrap yard, but the light still wont go out.

    Would the failed operation of one of the light units also cause the other to behave badly? Where is the unit located that controls the lights out delay after the door has been closed? Where might I find a wiring diagram of this circuit to try and trace the wiring for this circuit?

  6. #6
    Fellow Frogger!
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    Quote Originally Posted by P Zero
    I re-earthed the tail lights at the weekend. Problem solved with regard to the fog light indicator LED. It now does what its supposed to. Thank you very much.

    No luck with the interior light though. I removed all the door switches, and even replaced a couple of ones with corroded screws with ones from the scrap yard, but the light still wont go out.

    Would the failed operation of one of the light units also cause the other to behave badly? Where is the unit located that controls the lights out delay after the door has been closed? Where might I find a wiring diagram of this circuit to try and trace the wiring for this circuit?
    I presume both interior lights are remaining on. There may also be a time-delay-on relay in the circuit, to hold the interior lights on for a few seconds after all the doors are closed. This relay is energised by the ignition so the interior lights will go out either at the preset time delay, immediately if the ignition is on (car running) or as soon as the car is started.

    I don't know where this relay is located but if it has failed, the interior lights would remain on, or if an internal contact has become stuck. So I'd suggest systematically unplugging relays until you find it.

  7. #7
    Tadpole
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    If its any help, the lights stay on no matter what (unless you switch them off manually), and the lights on buzzer operates when the lights are on and the ignition is off, whith the doors closed.

  8. #8
    Fellow Frogger!
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    Quote Originally Posted by P Zero
    If its any help, the lights stay on no matter what (unless you switch them off manually), and the lights on buzzer operates when the lights are on and the ignition is off, whith the doors closed.
    OK it seems as if the first fault would be caused by failure of the time delay relay that is part of the interiior lighting circiut, i.e., the relay does not drop out.

    I just checked the operation of the interior lights and the alarm buzzer for external lights on my 405 and I think the second problem is probably caused by the first. I suspect that the same relay (for time delay) also forms part of the buzzer circuit.

  9. #9
    Tadpole
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    So if I just pull the realy out, the lights and buzzer should stop working? Is there another relay the same anywhere on the car that I can use to test if the circuit is working properly?

  10. #10
    Fellow Frogger!
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    Quote Originally Posted by P Zero
    So if I just pull the realy out, the lights and buzzer should stop working? Is there another relay the same anywhere on the car that I can use to test if the circuit is working properly?
    Yes to lights out and buzzer off.
    Second - that I can't say but I suspect not as (and I'm guessing because I have had no reason to go looking) the time delay relay is most likely a one off.

    Happy hunting.

  11. #11
    Tadpole
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    Thanks, I'll let you know how I get on.

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