Flasher unit failure

[old.bodger]

I lost all indicators on the Traveller (1970) checked the supply to the flasher unit and had good supply. Nothing out of the flasher unit. I replaced the unit - old one had B P and L on the end new one had X P and L
I made the following bold assumption :

P = P = Stalk warning light (lt Green wire)
B = x = Supply ( Dark Green)
L = L = Lights ( Green Brown trace)

All seemed to work

Did a short run to test another issue and started to notice irratic indicators and strong smell of 'something too hot', on investigation I find the flasher unit is cooked (I opened the can to see - also opened the old one and it is in the same state.)

I assume from the wiring diagram that it's all very simple and the most likely cause that I can think of is a grounded wire to one of the lamps (Bit odd as they all did flash when I checked them??) or rather improbably a bulb with an internal short.

It all got hot enough to make the rubber covers on the spade connectors melt. When I attempt to trace the fault (with a new flasher unit )should I include a temporary inline fuse in the circuit and remove later?

I assume that a check can be made of the circuits by 'injecting' 12v neg (positive earth car) down the various light supply / stalk wires and selecting the side of the car to test with the indicator switch.

Wisdom appreciated and apologies for long post!

[mike.perry]

Your wiring is correct, ref Workshop Manual P. N44
Try disconnecting the green and green/brown from the flasher unit and connecting them together. Turn the ign. on and try left & right indicators.
They won't flash but should stay on whilst you look for any wiring faults. If you don't find anything wrong then it looks as though you have a couple of dodgy flashers.

[bmcecosse]

That's the advice I would give too - eliminate the flasher unit while you search for the fault. But it should have blown the fuse if there is a short - so inspect the fuse box to see if nails have been fitted inplace of fuses!

[rayofleamington]

I assume that a check can be made of the circuits by 'injecting' 12v neg (positive earth car) down the various light supply / stalk wires and selecting the side of the car to test with the indicator switch.

Rather than wire it directly, you could hotwire the 2 terminals with a 5A fuse. The 2 bulbs on each side should draw less than 5A
2 x 20 =40
40/12 = ~3.4A

Thertefore if one side blows the 5A fuse they will likely be drawing twice (or more) current compared to normal.

Alternatively if you have a volt meter that includes a 10A current measure you could use this - but it won't help the meter if the current is over 10A!

Bulbs can go partial short circuit but my first guess would be a short in the bulb holder itself.

I once fitted a new stop/tail bulb after a major rebuild for the MOT. The tail lights worked and the stop lights worked so I didn't see a problem... The stop and tail were shorted insde the bulb so the stop lights activated the side lights - and I got an MOT fail
I spent an hour checking the wiring before I tried different bulbs