Flasher Unit Relay

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Zeke_
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Flasher Unit Relay

Post by Zeke_ »

Hi,

I am having some issues with the indicator pilot lamp (the one on the indicator stalk)

I recently replaced the flasher relay unit in my 1970 4 door, and the indicator main lamps work fine, however am unable to get a flash from the pilot lamp. I have tested the bulb and stalk unit, and testing on the battery lit up fine. However, when testing on the P terminal of the relay (and the ground of the bulb connected to the negative terminal of the battery) I was unable to get a response from the bulb.

What should I be expecting to see when a bulb is connected to the p terminal of the relay and the bulb is grounded?

The flasher unit I have is linked below, am wondering if It is a fault with the new unit

https://www.morrisminorspares.com/elect ... ly-p829880

My car is a 1970 4 door, with negative earth, alternator conversion (stock wiring elsewhere and no hazards or other modifications) and am testing a replacement indicator stalk, to make sure it works, when installed. (someone has mauled the bulb connector in the currently installed stalk)

Many Thanks for any suggestions on the issue, and one last question, are the electronic type replacement relays any more reliable from the factory?

Zeke

(sry for the paragraph)
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geoberni
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Re: Flasher Unit Relay

Post by geoberni »

This is how the conventional, bi-metalic strip 3 pin Flasher works.
The electronic one should replicate this without relying on the current draw of the circuit and the heater aspect.
Flasher.JPG
Flasher.JPG (19.36 KiB) Viewed 751 times
P = little indicator lamp inside car, wherever that is dash, stalk etc
X = live 12v
L = output that goes to the Indicator switch selecting Left or Right.

Diagram shows Unit with NO Turn Selected
1 - When a Left or Right turn is selected, L is going to earth, via the indicator lamps of the selected side.
That completion of the circuit Battery - Flasher - Selector Sw - Lamps - Earth causes the small heater in the Unit to warm up the Bi-Metal strip. The resistance of the heater element compared to the lamps, prevents the Indicators actually illuminating.
2 - Once warmed, the Bi-Metal strip (2 metals fused together which have different expansion rates for the same amount of heat applied) bends toward the fixed contact.
3 - The Contacts close, one set supplies the P terminal, the other bypasses the little heater, so the Indicators Light up, but the Bi-metal strip immediately cools down.
4 - Once it's cooled enough, the strip opens the result being A) the supply to the P terminal is lost & B) the supply is back through the little heater, so the Indicator Lamps are 'off'.
This sequence continues approximately every second until the Indicator switch is turned OFF braking the overall circuit.

Electronic Units replicate this so that they do not rely on the heater aspect.
When LED Lamps are fitted, the whole balance of the overall Battery - Flasher - Selector Sw - Lamps - Earth is destroyed and insufficient current through the heater stops a conventional Unit working, it just never heats up.

So just get a test lamp or meter and see if there is anything on the P terminal when the Indicators are flashing. If there's not, then the Unit is duff.

As to reliability, I think quality is variable with small electronics these days, but I'd like to think ESM is reliable stock.
Basil the 1955 series II

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philthehill
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Re: Flasher Unit Relay

Post by philthehill »

The ESM link states that the indicator unit is for Negative earth vehicles only and you state that the car has been converted to Negative earth so if connected correctly the indicator light should light up. It could well be a faulty unit.
There was nothing wrong with the Lucas flasher unit as originally fitted. They were well made and reliable.

Zeke_
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Re: Flasher Unit Relay

Post by Zeke_ »

Thanks for the advice,

Ordered a digital type replacement, as am not sure about the wattage with the bi-metallic strip (even though I don have hazards installed), will report back if this solves the problem.

Many Thanks,

Zeke
JOWETTJAVELIN
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Re: Flasher Unit Relay

Post by JOWETTJAVELIN »

x2 21w = 42w
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