Triumph Repair: flasher indicators, wattage bulbs, direction indicators

Question
Hi Howard,
Problem i have is on a `79 Spitfire UK version. The indicators failed the M.O.T as they were flashing rapid and unregular flashs. I have checked all earths back ones were fine but cleaned them in case the front side lights were slightly rusted so replaced with new units also changed the relay which is under steering wheel replaced all bulbs with new. All othe relectrics are fine the hazards run off the same relay on this model and they were fine and a clear click is coming fron the relay but the direction indicators don`t make a distinctive click but do flash. One thing i have just come across is that the battery is a 60AH which in the manual says should be 40AH could that be the problem i doubt it but i`m starting to grab at straws here now...so if you can give me any tips would be great...trying to get it ready for the MOT before 10 days runs out...

Cheers if you could help with anything else to check
John

Answer
Hi John,
I have not worked on many UK version British cars but every British car that I have worked on, operated the turn signals the same way.

That is the flasher that actually makes the lights blink works on resistance of the bulbs. The amp hour rating of the battery has nothing to do with it. However the charge rate can affect the resistance so you should test the charge rate and also do voltage drop tests of the power side and the ground side (ground strap of engine to body and body to negative post of the battery)

Current always takes the easiest rout and if a turn signal is on and there is high resistance in a ground for the charging system then the current will try to ground through the flasher unit to the bulbs thus making the flash more rapid. Another possible is the wrong wattage bulbs if the Wattage is too high the heating element in the flasher will heat up too fast making the flasher operate fast.

If your car came to me in a shop I would first check battery voltage (about 12.5v) then start the engine and set it at a fast idle and check the voltage 913.8 to 14.5v) Then turn on the turn signals and check that all bulbs are flashing including the dash indicator light. Note the flash rate and turn the engine off and turn the ignition back on but don't start the engine and note the flash rate. Now restart the engine and use a volt meter on a very low scale and start doing voltage drop tests on all the power cables starting at the battery post (not the cable end) and check for low voltage between the (+) post and the positive post on the starter solenoid and check for voltage between the engine block and frame and between the engine block and the (-) post (not the cable end) of the battery.

If all that checked good I would have had to remove all the bulbs and read the wattage. (Flasher bulbs should not be higher than 21 WATTS and the indicator light should not be higher than 2 WATTS)

If all that is OK I would take your wiring diagram and do voltage drop tests on the flasher circuit all the way from power to load.
Howard