Indicators, Hazard Warnings and Related Topics

 Prior to the 1950s, semaphore indicators and hand signals were the means of communication between road users – we have moved on since then! Or have we? A few months ago, traveling behind an MGB, the driver having clearly failed to cancel the right indicators, we happened to pull into the same petrol station followed by a group of young men in a clapped out modern car. Repeatedly and violently thrusting their index fingers skywards, these ‘pleasant’ lads were clearly trying to attract the attention of the offending MGB driver, I imagined, to inform him. ‘’You silly fellow, were you unaware that your right indicator was flashing and you were confusing other drivers’’ – or words to that effect! More later about indicators left on.


Some time during the 1950s, semaphores were replaced by flashing indicators.  This was obligatory.

 The car manufacturers of the day rose to the challenge and produced flashing indicators controlled by dash-mounted, manually operated and mechanically timed switches – not the best solution!  Innovation and progress led to the self-cancelling, steering-column mounted indicator switch.  Unfortunately, early versions of this ‘device’ proved not to be reliable; we have all witnessed examples of this. The encounter of the ‘silly fellow’ is an example of possible repercussions.  Clarkson would say ‘’That’s normal for anoraks’’.  In some respects I must agree, it certainly doesn’t do much for the cred of the classic MG driver.


Incredibly Hazard Warning only became compulsory around 1970.  Owners of cars manufactured prior to this date resorted to a warning triangle.  How important is Hazard Warning?  From my experience I would say very important!  Returning from Le Mans in 2001, travelling on the M3 at 9 am the inevitable happened.  Cough, cough, loss of power, but fortunately enough momentum to come to rest on the hard shoulder – not a good place to be at peak rush hour on a wet Monday morning!  The cause of this hazardous and traumatic situation was due to – guess what – the evergreen and all too common petrol pump failure!  Far too dangerous to resort to the time honored solution – a whack with a hammer. I knew, statistically, that I had 20 minutes before my ‘C’ roadster would be reduced to half its length. At that point I would have sold my soul for hazard warning.  A call from my mobile brought help in the form of a tow truck, which incidentally only towed me off the motorway, leaving me to find my own way home.  Some three hours behind schedule my car and I were safe at my home address; I won’t bore you with the details of how I achieved this. After this harrowing experience I was in no doubt that Hazard Warning would have reduced  at least some of my anxiety.  I subsequently designed my own Hazard Warning kit now fitted to my two MGCs. 


Now to the point of this month’s article which is to ‘review’ the Indicator and Hazard Warning circuits.

Referring to Fig 4 you will see that primary circuits ( covered in previous articles) are shown dotted, these are circuits (brown, green, white &  purple wires) connected to fuses, the ignition switch or directly to the battery. The Hazard Circuit is fed from a brown wire therefore requires an in line fuse & the Indicator circuit is supplied by a dark green wire from fuse 2 & is switched by the Ignition switch.

The introduction Hazard Warning necessitated a ‘device’ to switch between the Indicator circuit & the Hazard warning circuit, hence the Hazard Warning switch. How does this switch relate to these two circuits?

Hazard Warning circuit. Fig 4 shows the Hazard switch in both the ‘ON’ position & the ‘OFF’ position &

 shows how it is interconnected & what it does, see Fig.2.


When switched ‘ON’: 

a)      12 volts are connected from the battery via the in line fuse to the Hazard switch (terminal 5).

b)     The left & right indicators are connected together (terminals 3,5 & 6)

c)      The supply to the Indicator flasher unit is removed (terminals 2 & 4).

When in the ‘OFF 

a)      12 volt supply is connected to the Indicator circuit (terminals 2&4)

b)       The connection between the left & right is removed (terminals 3, 5 &6).  


This information should be of use when tracing faults in both the Indicator & the Hazard Warning circuits.

The flasher units are the most common cause of problems, these are easily replaced.

A simple method of testing flasher units is to remove the connecting wires & connect them together (green wire to light green wire).  Now turn the ignition ‘on’ & operate the indicator switch, the respective indicators should ‘come on’ but not flash. Likewise to test the Hazard flasher remove & connect the brown & light green wire together & turn the Hazard switch ‘on’, all four indicator lights should ‘come on’ but not flash.  Remember also to test the in line fuse (10 amp). Note also that the Hazard flasher is 4 x 21watt & ) & the Indicator Unit is 2x 21watt.


 ‘AFTER MARKET’ HAZARD WARNING & BLEEPER (To warn if indicators are not cancelled).

SEE FIGS.3 & 4. Fitting a warning Bleeper takes about 10 mins & simply involves connecting the Bleeper to the existing  Indicator flasher unit. To fit Hazard warning takes a little longer (about 30 mins) & involves

drilling a 12 mm hole at the side of the centre consul (or under the dash below the fuel gauge) to fit a small

red flashing toggle switch - that’s all you see. Just three connections to the ‘bullits’ under the steering column & the job’s done. I can supply both a Hazard kit & the Bleeper. Give me a call  

Phone 01582 832305  or email    Andy Capy


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