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MG MGB Technical - hazard lights too fast

My hazard lights are too fast (failed mot on this) what is the problem: I have tried a new unit still the same-is it an earthing problem?
P Hobson

This is generally, as far as I know, due to too high a resistance in the line. On my tow vehicle, when I hook up my trailer, the indicators flash much faster. I'm told this could be remedied by installing a heavy duty flasher unit. I haven't done this, as I find it reassuring to be able to check at a glance that I've still got a connection to the trailers brake/indicator filamen. Sometimes (often) the bulb burns out and this gives me immediate warning to change the bulb or check the plug.

Having said all this, yes, you might have a poor earth/ground. Do the LS & RS indicators flash at a reasonable rate? Did you try a heavy duty flasher or just a standard one?

Good luck.

TTFN

Derek Nicholson

one thing to check is that the hazard flasher is rated for all four indicators....i know in the past i have been caught out by getting indicator and hazard relays mixed up, they are load sensitive and you may have ended up with a hazard unit rated for more bulbs...if that makes any sense. I'm sure someone else will be able to explain it better..
jon

Sounds like you have an indicator flasher in there instead of a hazard flasher. The hazard flasher is designed to be load independant as there is no way of knowing how many lights are still working after, say, an impact. Likewise they are largely voltage independant as they may be left on for a long time at the roadside without the engine running i.e. running the battery down. By contrast OEM turn flashers are designed to run two bulbs only, and give a different flash rate if one of them has failed. In the MGB era the 'flash rate' with one failed bulb is actually not flashing at all, but permanently illuminating the still working bulb. This actually made them rather sensitive to voltage, and in older cars like the MGB high-resistance connections can develop which reduces the voltage/current at the flasher making them slower and slower, or eventually stop. Modern electronic flashers are much less sensitive, and flash at double-speed with one bulb out (it is a pity that some drivers are also insensitive and don't even notice it). But if two flasher units give the same results, and the replacement is *definitely* a hazard flasher (what happens with 1, 2 and 3 lamps disconnected?) then it could be a wiring fault. But since a hazard flasher is designed to flash at more or less the same rate regardless of whether 1, 2, or 3 bulbs are *disconnected* it is unlikely to be anything out towards the bulbs, especially if the indicators work OK. It could be a bad connection in the 12v supply to the flasher, or in the switch. Bypass the flasher unit, switch them on and you should get a constant glow from the bulbs. Then measure the voltage at the flasher unit terminals and the switch (not the green wires). If you see 12v then it is definitely the flasher unit, regardless of a replacement doing the same thing. Less that 12v on the flasher terminals indicates a bad connection back through the in-line fuse in the brown circuit. 12v on the flasher terminals but not the switch termianls is a bad connection between the two. 12v on some switch terminals but not others is a bad switch, which can be dismantled and cleaned.
Paul Hunt 2

This thread was discussed on 17/08/2006

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