Flasher Can Question

addo · Post by **addo** » 18 May 2011, 21:01

Seriously...

When a bulb is blown, why does the flasher flash faster?

Trying to get my head around an issue on one car.

Cheers, Adam.

Xaccers · Post by **Xaccers** » 18 May 2011, 21:02

Because there's less load on it.

addo · Post by **addo** » 18 May 2011, 21:04

So if the flasher circuit wire was dead shorted to ground instead of passing through any bulbs, it would never click off?

Post by **CitroJim** » 18 May 2011, 21:27

No, a fuse would pop... Unless the flasher has overcurrent protection built-in.

The flasher rate increase when a bulb blows is deliberate so that you know a bulb has blown.

It was a handy and lucky side effect of the old-type bimetallic electromechanical ones and nowadays the same functionality is done with electronics inside the flasher unit.

Interestingly, although the unit will flash fast with less load (because a bulb has popped) they don't now flash slowly if the load is increased which is why when wiring trailer socket you no longer need a heavy-duty flasher unit. All you need (by law) is the audible warning unit to let you know if the trailer flashers are working.

addo · Post by **addo** » 19 May 2011, 03:15

OK, I'll describe the sitcheration:

Both sides of the flasher circuit are fed by the same relay arrangement.

Left flashes normally.

Right gives a frantic click-click-click without a single flicker or even a dim glow from any RH globe including the dash telltale. Ditto when the hazards switch is depressed - which uses the same relay box.

Post by **Paul-R** » 19 May 2011, 09:33

Without getting bogged down in theory I wouold first of all take out the indicator bulbs (including wing repeater) and give them a test on a 12v supply.

Then I'd check the bulbholders for voltage when the can is flashing. After that I'd start tracing the physical route that the cables take.

Only then would I start troubling myself why it was all happening!

(BTW, I agree with Jim on the history and reasons)

addo · Post by **addo** » 19 May 2011, 10:43

I tried the "nutshell summary" of your tests.

With all external bulbs out, the dash telltale blinks madly (at least it works!) but when any RH bulb is reinstalled the click rate increases to a point where there's no dash telltale or exterior flashing.

It's a right bugger!

Post by **Paul-R** » 19 May 2011, 11:15

If it's flashing like buggery with all bulbs removed (save the dashboard one of course) then you're going to have to look closely at the wires.

Before doing that try linking the live and output wires across the can and see if any of the bulbs light up on the RH side. I'd do the test in the following order: 1) see if LH bulbs light continuously, 2) see what happens with no bulbs on the right (be prepared for a fuse to blow) and 3) see what happens when the bulbs are in position.

A 10A (or even 5A) fuse to do the bridging is not a bad idea.

Can you put a multimeter in ammeter mode across the connections to see what curremt is drawn comparing left to right?

addo · Post by **addo** » 19 May 2011, 11:51

Thanks Paul; ammeter idea is brilliant - can probably test at the column stalk connections.

The flasher can is actually one of those monobloc relays with the back of its socket all but inaccessible. As a fallback I could make a "breakout" harness with siamesed relay sockets tailed to male spade lugs individually inserted.

Also going to check out the aftermarket towbar wiring in case there's a chafed wire hiding.

Post by **Paul-R** » 19 May 2011, 11:56

addo wrote:Also going to check out the aftermarket towbar wiring in case there's a chafed wire hiding.

That's definitely an "Oh, by the way" moment there!

addo · Post by **addo** » 21 May 2011, 08:31

Fixed for now.

Unplugged blinkers witch, jumped from a full time hot and checked amperage each side after looking for a chafed towbar harness. All good; near-perfect current symmetry.

Tinkered with the switch and found carbon/wear to the contact buttons - a halfarsed polish of the buttons then a squirt of contact cleaner/deoxidiser sorted it.

Hazards have the same fault (as they did always); it was deceptive before as I thought one might be affecting the other - now I know it's duff internal contacts...

Nice to get something sorted.

Post by **Paul-R** » 21 May 2011, 17:25

Excellent job there Addo.

Sometimes you just have to know what's good before you can narrow down where the bad is.