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HeavyB
07-06-2005, 11:39 PM
I have a '76 TR6 with low original miles. Just noticed in the last couple days that the turn signals do not flash when the engine drops down to idle revs. If revs push up the turn signal begins to flash again. Only recent electrical change was to replace the old sealed beam headlights with halogen sealed beams from Moss. Any ideas why this is occurring would be appreciated.

Paul Johnson
07-07-2005, 12:02 AM
How odd. Was going out tomorrow to diagnose turn signals that quit working for no reason. I also have just put in sealed halogens. Follow up coming.

Andy Blackley
07-07-2005, 12:31 AM
There is no direct connection between the headlight and the turn signal circuits. Sealed beam halogens should not take too much extra amperage to operate. I just replaced the turn signal switch on my TR250 this evening and noticed that the circuit was sensitive to any excess resistence in the line. In my case the right front TS bulb had rusted itself into the socket. A new bulb and a good cleaning of the socket and ground had it operating again normally. I have sealed beam halogens (as opposed to Hellas/Cibie etc which use more juice) and have not had any problems with amperage dropping off at idle speed because of them.

AltaKnight
07-07-2005, 12:37 AM
I assume they don't flash with the turn signal lights staying on solid. If so it sounds like there's not enough juice getting through the flasher unit to the lights to heat the flasher bimetallic strip up enough to break the connection.
Could be the new headlamps are sucking up more power and/or if it happens without the headlights on then you may have (1) poor connections on the flaher unit (2) a weak battery or (3) an alternator not putting out enough or (4) it could be as simple as a poor ground on the battery cables or (5) poor ground on the turn lamps.
Course it could just be (6) the flasher unit on the way out. So many choices /ubbthreads/images/graemlins/frown.gif

Paul Johnson
07-07-2005, 07:04 PM
"How odd" in the coincidence of events, not that I thought there was any connection between h/l and turns. In any case, mine did nothing, h/l on or not, engine running or not.
So, as an old master tech and corporate trainer, the task was simply to look at the schematic first. Switch gets its power from the flasher unit, which gets it from the hazard switch. Since the hazards work, I tested for power at the flasher. There being none, then the only possibility was a loose connection at the switch or an open in the wire between the switch and the flasher. Connection being the most likely, I checked that, and cured the problem.

big6
07-07-2005, 08:18 PM
If you calculate the total amperage required with lights on, turn signals on, brake lights on, engine at idle you will understand how marginal the stock charging system was designed. The other concern is when amperage is high and voltage is low resistance is high thus switch contacts get hot. This is one reason why Lucas switches fail. Halogen lights do consume more power than standard sealed beams. The fix is to install a higher amperage alternator. I installed a 100-amp alternator on my TR6 and killed just about all of the Lucas gremlins. The change is relatively simple and highly recommended. The alternator I selected fits a 1990 Chevy Beretta.

HeavyB
07-07-2005, 10:03 PM
Thanks for the input, Paul.

HeavyB
07-07-2005, 10:20 PM
Thanks. I suspect this may be the problem.

piman
07-08-2005, 05:33 AM
Hello Big6,
you seem to be a bit mislead with your electrical information.
If voltage is low, current is also low and in the case of lighting circuits, as the resistance varies with filament temperature, a lower applied voltage means lower filament temperature and higher resistance and less cuurent, i.e. it is not linear. Halogen light units do not use more current than sealed beam units either, unless you install higher wattage units when doing the change. Halogen units run hotter and are more efficient, i.e. more light for the same current.

Alec

Adrio
07-08-2005, 10:18 AM
I must agree with piman, sorry big6 but piman is correct in his statement about teh relationship between current, voltage and resistance. What you folks are trying to put into words is called Ohm's Law. The technical wording of this is:
The potential difference (voltage or V) across an ideal conductor is proportional to the current (amperage or I) through it.

The constant of proportionality is called the "resistance", R.

Ohm's Law is given by the equation: V = I*R

The comment of the fileament not being linear because of themal effects is also correct. In an incandescent lamp (the kind employing the principle of electric current heating a thin filament of wire to the point that it glows white-hot), the resistance of the filament wire will increase dramatically as it warms from room temperature to operating temperature. If we were to increase the supply voltage in a real lamp circuit, the resulting increase in current would cause the filament to increase temperature, which would in turn increase its resistance, thus preventing further increases in current without further increases in battery voltage.

big6
07-08-2005, 11:01 AM
E=IR...

BOXoROCKS
07-08-2005, 11:02 AM
Boy, it looks like a bunch of young guys in the Brit car world.
Unless your left arm is broken,...you got turn signals.

Adrio
07-08-2005, 11:11 AM
Thanks for calling me young. That has not happened in a while even though I still feel as young as when I first got my TR3 in 1980.

I threw the Ohm's Law etc. in there just out of obligation to myprofession as an electrical engineer. For some odd reason I felt compelled but in more of a jokular vein. I trust this fun group was not offended.

piman
07-08-2005, 01:01 PM
Hello Adrio,

as you are probably aware, there is a common misconception that the stated wattage is assumed to be fixed and using the formula of wattage = volts times amperes, then if the voltage goes down the current goes up, which of course is not the way of things. Lower voltage = lower current = reduced wattage. Certainly some people will have come across reduced voltage in electric motors giving rise to an increase in current, but that is due to an entirely different reason and does not apply to resistive circuits.

Alec

Adrio
07-08-2005, 02:36 PM
piman, you hit the nail on the head. If some one were to assume the wattage was the fixed value then that is how the misconception would occure. Well stated, I tip my hat to you for being able to say it so clearly.

BOXoROCKS
07-08-2005, 08:21 PM
Ha ha ha ha ha, very good Box, that was funnie,............... geesh you guys.