Retrofit Flasher debug

I have a couple of old cars with flashing indicators.

The Triumph has a simple 2-terminal flasher unit and it has right and left indicator lamps on the dashboard and front, back, and B post external lights. It seems to depend on the right amount of resistance from the bulbs to operate correctly, so that if one bulb fails then the dashboard lamp doesn't flash, it stays permanently on and the bulb that hasn't failed also stays on. The only conclusion I can reach is that the total resistance and therefore the wattage of the indicator bulbs is a key feature of the correct operation. The wiring diagram is a bit complicated with dimming relays for night use so this looks a dead duck as a model for a retrofit.

As you seem to be using a single dashboard lamp to indicate the flashers are working, then you probably have a similar set-up to the Morris Minor, which has a single bulb in the stalk and an external front and rear lamp, each 21W. Again I would expect the wattage to control the rate of flash, but I haven't yet had a failed bulb so I don't know how the system behaves under those circumstances.

However - there are two types of flasher unit, the bog standard one and the electronic one. Don't go for the electronic one.

The bog standard one has internals like this

1. "L" another different coloured wire (usually Green&Brown) sends power

Check each light unit for a good earth and the correct wattage bulb.

Good luck!

Jim

Thanks. You have confirmed what I have, and have tried. The three pins on the flasher are labelled, 'L' and 'X', with P being the Pilot lamp on the dash, as you say. As this is a Positive earth system, 'X' and 'L' are reversed, and the instructions say this. Everything behind the dashboard seems to be correct, so the next stage is, as I said, a complete and detailed check of each separate component. It might have to wait until autumn, as I at least have flashing indicators, and once started, the investigation could take some time, with who knows how much disruption to driveability.

My Morris is Positive Earth and the B (or X) terminal goes live with the ignition and the flashers and dashboard indicator bulb work like that. Provided you haven't got an electronic flasher unit, there is no need to worry about the polarity and the diagram I provided of the internals of the mechanical type does confirm that the B (or X) is designed to be the common which is always powered. The L terminal is designed to feed the electrical load.

The set-up I found will work provided the flasher load when switched on totals 42W. Whoever suggested reversing the two had an electronic version in mind, and if you have the electronic version, please replace it with the mechanical one I found on the internet for you, because that works on either polarity provided it is correctly wired.

Jim

The instruction to reverse the 'X' and 'L' terminals is included on a piece of paper included with each of the different units I have tried. Connecting them as if on a negative-earth system results in no flashing, which is what the paper says will happen. I have now tried units from three different suppliers, one from Vintage Car Parts (actually three from them, all behaving the same way, and two from different local parts suppliers. They all have exactly the same piece of paper concerning the terminal swap, even though there are differences in canister size. There has never been an electronic unit involved, nor considered. Your second link does not show any image, even if I use Chrome, which is usually pretty unfazed by awkward links. Assuming that there is supposed to be an image, of course. I like the price, though, that is cheaper than all the ones I have tried! I am sure that my problem is some version of bad joint or contact, or bad or missing earth, and that is how I will approach it. Unfortunately, the gentleman who installed the flashers is now dead, so I can't ask him anything. And I don't think electrics were his particular forte, anyway. I will report what happens when I finally take the system apart. Thanks for the thoughts.

I have just looked in the Morris Minor workshop manual, and the standard fit was a Lucas FL5 for both positive or negative earth systems, and both polarities are wired exactly the same.

If any of yours are marked with that part number, that is the one to use. If you want a bullet-proof solution, that is the one to buy.

The flasher diagnosis in the manual is to connect a volt meter between the B terminal and earth and it should show 12V when the ignition is on and 0V with it off.

Next it suggests checking the flasher bulbs, which should all be 21W because the flasher unit will only be activated properly by a 42W load. Then temporarily connect the B terminal to the L terminal and turn on the ignition and the Right and Left circuits can be individually checked for the bulbs being permanently on. Any that don't light are either a dud bulb or a bad connection either to the bulb or to earth.

If all the bulbs are sound and light, disconnect from the L and connect the B to the P. Then with the ignition on the panel bulb should light. If it doesn't, then it is either a dud bulb, or a bad connection to it, or the fitting not earthed.

If all the tests prove OK, then without the temporary connections from the B terminal and with the ignition on, the right or left flashers should go on and off and the panel light should do the same. If that is not the case, the flasher unit is faulty and should be replaced.

As for the internals of the flasher unit, click on this link

Thanks, there is useful debugging information there. I will print it out immediately. I'll look for part numbers, but that onw you quote does not sound familiar, the ones I have tried are all modern reproductions.

I will report progress (if/when there is any).

Big snip. There is news, and it is unexpected. I had already started to do my debug process, as outlined earlier, separating each lamp and seeing what happened. Using basic electrical equations, Watts = Volts x Amps, and Volts = Amps x Ohms, 12 V and 21 Watts means a current of 1.75 Amps per bulb. Resistance per bulb is 12 / 1.75 = 6.86 ohms. Two bulbs in parallel should be 3.43 ohms. I removed the wire sending power to the switch from the flasher, and connected my ohm-meter between it and earth. Correctly, it showed infinite ohms when the switch was in 'neutral'. Moved to the right side, it now read 11 ohms. so did the left side. The rear lights are easily accessible, as is the driver's side of the car, so removed the right rear indicator bulb, which has '23W' written on it. The ohmmeter indicated the resistance as 1.3 ohms, very different from my calculated 6.86, so there is something wrong there. The right front indicator, as reported by the meter now, showed 16.3 ohms, again very different from 6.86. On reassembly. the total resistance now read 8.7 ohms, rather than 11. Repeating this for the left side gave 1.2 ohms for the rear 21W bulb,

I did a bit of reading around, and your flasher that has the tell-tale permanently lit when the indicators are off is for an MGB. That car has additional wiring on the indicator stalk and left and right tell-tales and the idea is to have everything off until the indicator stalk is used, when the correct tell-tale will be lit when the flasher bulbs are off, and off when the flasher bulbs are lit. Imagine that the L and P terminals are two poles of the same switch and the output swaps between the L and the P. That unit will be no use to you because you have a single tell-tale.

As for your Araldited bulbs, you have my sympathy. I once bought a car previously maintained by a DIYer who butchered everything he touched. Everything I maintained after getting it had been reassembled wrongly and it took over a year before I considered I had found and corrected all of them.

Araldite is difficult to remove once it has fully cured as it becomes very solvent resistant so it cannot be readily dissolved. The best way to help remove it is to heat it. Above 70°C Araldite will start to soften making it easier to scrape away. It will still come down to using mechanical removal to get it off. A soldering iron is a good way of getting the heat to the adhesive.

As for your bulbs, I would be inclined to buy a set of 21W bulbs and replace all the ones currently installed. Whilst I can't fault your arithmetic and your use of Ohm's Law, you do have to bear in mind that in most metals the resistance varies with temperature. Hence my advice to start with the correct bulbs and go through the diagnostic process I provided earlier rather than trust the results of resistance measurements.

Good luck (I think you will need it!) Jim

Dont waste your time using an AVO meter or anything similar to measure the resistance of any lamp which has a filament. When it comes to life its literally white hot, and the temperature shift will throw the "real" resistance off the scale.

Actually, theres probably nothing wrong at all

I had indeed wondered if there would be any effects on the indicated resistance, but as this is DC, I thought that they would be small, and not subject to the shifts associated with AC. But I accept that temperature will have an effect. I will indeed start with new bulbs, at least for the front lights, as they are an unknown quantity. The rear ones are not so unknown, as the lamp clusters are recent and currently available. But then...

See other message re: New bulbs, I am not looking forward to the de-Araldite process, It might even be easier to buy new insert bulbholders. At least I would know that there is no Araldite anywhere near them, and I would be starting from a known position. My attempt to see what I could discover has suddenly become an extended event.

Today's news. I did some checking, using the DVM as an ammeter, and removing each of the rear lamp flasher bulbs to compare 1-bulb and 2-bulb readings, side to side. But while I was doing this, I noticed that, with the plastic red and amber 'glasses' removed, there was considerable "cross-talk" between rear left and right bulbs, including the tail light bulbs. Adding a temporary earth jumper to either of the actual lamp casings improved this, although there was still a small glow of one tail-light bulb when there should not have been. Not having any correct wire for a new earth wire, I used a piece of spare wire, and ran a dedicated earth connection from the plate to which the rear lamp housings are bolted, all the way to the battery box behind the engine firewall. And it has had a strong effect fixing the glowing bulbs that shouldn't. The flasher pilot light still flashes weakly even when no direction is selected, but: a) This is still the same flasher which did that before; b) I don't know if this flasher is now damaged. I will try other units the next time I go back to the garage.

It would be worth looking at the earth (positive) connection from the battery. The starter motor draws about 180 Amps when starting the engine, so there needs to be a connection (often braided wire) from the battery to the engine block. On my Triumph it is a daisy-chain going to the chassis and on to the engine. On the Morris the battery goes to the chassis, and a separate braided wire goes from the chassis to the engine.

This is because the engine and transmission are on rubber mounts, and there won't be a good connection between engine and chassis. I remember some years ago, my brother owned an MG Magnette. It started OK but the starter motor always sounded sluggish. We were doing some work on the car together one day and I asked him to start the engine, and as the starter motor kicked in the choke cable glowed bright orange. The car was using that route to get the earth connection to the starter motor. There wasn't another link from chassis to engine! A short bit of hefty wire from the chassis side of an engine mounting to the engine side of the same mounting fixed the problem and the starter motor was much more energetic.

From your description of what happens with your flashers and the wire to the battery as a solution suggests that the chassis earth connection isn't good enough. It either hasn't got an earth connection to the chassis or there is one but it is corroded and is not a good connection.

Out of interest, what is the car you are working on?

Jim

snip

It is an HRG, which has an aluminium body on an ash frame. The chassis, however, is steel, and it looks as though the earth connection would be fine, as there is a continuous metal run from rear number plate to the battery connection. However, there could easily be a problem where paint interrupts the connection, which is what I suspect is/was the case here. Although I know I have eliminated one problem, until I have a working pilot light, I cannot say that the circuit is totally fixed.

snip

I checked this today, and it has a proper braided earth strap linkng engine to chassis.

Actually, the connection I made is not at the battery, but on the battery box, where there is also an earth connection for the horns relay. That works fine, so no indication of a problem there.

The marque has a website, link here if you don't already know it.

Jim

Yes, I am a member of the Association. But this is not specifically an HRG problem, it is a Joe Lucas and an earthing problem. I do indeed take care of the car, hence my desire to get this sorted!

Update. I did some current-reading today. First, I bypassed the flasher, so that the bulbs would be at working temperature. The RHS is much easier to get at, due to the location of the car in the garage. Design:

RHS 2 bulbs read: 2.87 Amps, 4.18 ohms, 34.44 W. Remove rear bulb, so front only in circuit:

For the LHS, I did not bother with removing the rear bulb, but the two bulbs gave:

Somewhere, the resistance is high, or the bulbs are just not doing their job. With currents so low compared with design, it is no surprise that the pilot light won't flash. But I'm getting to the point of diminishing returns, lots of time spent, for little useful progress. I think I'll take a break from this.

I did some doodling while I was drinking a beer outside this afternoon and came up with the following idea: If I add a 10 ohm 10 watt resistor in parallel with the LHS flashers, that would bring the current passed through the flasher up to the intended value, as presumably required by the flasher to operate the pilot light correctly. Similarly, a 20 ohm, or 2 x 10 ohm, resistors would bring the RHS into compliance. In theory.

I took the car out for a drive this afternoon and on one occasion when I signalled Left to turn off the main road to go into my village, the car behind suddenly loomed large in my mirror, as though its driver had not seen the indicator light. I checked when I got home, the lights did indeed flash, so he was not paying attention. After all this work.