Flasher failures

The flasher unit on our trucks are prone to failure simply because the new ones are built with Radio Shack parts and appear to have no overload protection. The encapsulant hides all.
I dissected several units for an article a few years ago and since this subject comes up so often I thought I'd summarize my findings with a solution as well.

Image #1 below is a typical schematic. Simply an oscillator with a transistor driver rated at 15 amps.
The inrush current for 8 or 10 lamps (not uncommon with a trailer hooked up) can reach 75 amps and it's no wonder that the flashers fail.

My solution is to add an electromechanical relay to the circuit so that the flasher unit never sees more than the relay coil. Image #2.

In addition to protecting the flasher unit, the relay puts full battery voltage on the lamps, they are a bit brighter as a result. There is always a small voltage drop across a transistor.
The relays (one for the headlights also) have performed flawlessly for over a year now and the 4-way flashers were used extensively during my cross country trip.

Image #3 is the preliminary set-up to be used on the XM757 8x8. It may seem like an overkill, but I like it that way.

Merry Christmas!

PS. If you can find a flasher unit from the sixties, it was designed with a heavy duty SCR and could withstand an overload until a circuit breaker tripped....

ah yes.. there is a point where relays become contactors -and that's the place to be!

Yeah, I like them big. A 25 amp mil spec relay can handle a 10 amp "lamp load" with inrush currents up to 100 amps...

Bjron, where did you get those relays and how much, thanks

Ebay, of course, about $15/ea. Look for "aircraft relays". Surplusnut has 'em. Made by Cutler Hammer or Leach.

BTW, they are rated 25 amps, hermetically sealed and are good for the full mil spec temp range. Suite the deuce to a T.

Very good idea, this is a mod I would definitely like to do. I'll hafta watch for some relays.

Bjorn, I like the other turn signal mod you've done - where the low air buzzer 'flashes' on and off while the turn signals are on. How did you do that? Is there a thread here about it? Does the low air buzzer work the same as before when the air is low?

Jon

Jon, this is the easy method, only one diode and a couple of splices. Doesn't effect anything else, just adds the buzzer signal when your turn signals are on..

Thanks Bjorn!

I really feel like an idiot when I realize my turn signal is on after I've driven who-knows-how-many miles!

The buzzer may seem loud when engine is at idle, but on the road, with a headset/ear plugs on it's just right.
Even okay with 4-way flashers going on some long uphill drive. Never forget to turn them off.

The green indicator light is hopeless, in bright sunlight you can't see it and at night it's blinding.

Bjorn, in your rewired flasher schematic, the 24v is tee'd to feed the flasher as well as the relay contact. Did you end up putting a circuit breaker in there somewhere to protect the flasher? It seems that if the relay was slower than the flasher, or if the relay quit working, an overload would still blow the flasher.


I had a short in some trailer wiring and ended up frying my flasher. Then, before I figured out the problem, I hooked up an old flasher that was intermittent and fried it too. They both went open circuit. Since I had an event last weekend and no time to get a replacement, I had to jumper the connector and manually flash my turn signals. The flasher seems like a poor design, especially for an MV.

Well, the flasher never sees any load other than the relay coil, so it should not get exposed to any overload or short in the light circuit.

Oh, duhh, I see it now!

After my last incident, I located an aftermarket replacement turn signal flasher. It is made by TruckLite, UltraFlashII model, and works on 12 or 24 volt systems. There are 2 models:

#97231 Flasher WITHOUT audible signal
#97232 Flasher WITH audible signal

Here are the specs:
25 amp max load @12.8v
solid state, completely sealed in polyurethane
LED or incandescent lamps
12 or 24v operation
built in short circuit/overload protection

I cannot find the receipt, but I think I bought it from Ryderfleetproducts.com. It was $45 or so IIRC. I only put one on the tractor, as it is most likely to be doing towing duty, whether it be a trailer or towbarring. Plus the deuce's flasher is still working. I didn't hack the stock harness, I modified the dead original flasher to use as a mount and connection point for the new flasher. It is mounted up high on the firewall in the passenger compartment, so is not really noticeable, plus I painted it all black.

Truck-Lite makes a 24 volt flasher p/n 97315. This was difficult to get , but you can go to any Truck-Lite dealer and order p/n 97232 . This is a 12/24 volt heavy duty, solid state, short circut protected flasher . I put one on my duece and it works great. It only costs about $20 , half of what a military replacement flasher costs . Hope this helps.

cranetruck said:

Jon, this is the easy method, only one diode and a couple of splices. Doesn't effect anything else, just adds the buzzer signal when your turn signals are on..

Click to expand...

Bjorn, Can you provide some specs on the diode? I'd like to do this mod, and your flasher mod also.
jonathan

I just replaced my flasher yesterday with one from napa. It was from Grote. $25

Vincent,

Got a NAPA # for us to ref?

Kurt

I often thought about going this route, but I only had a couple fail and got a used one to fix the problem. I just dont have the heart to cut the factory wires. If I can tet the connector out of my old flasher, I would be al set.

Flasher is made by Grote. Napa part #263-4. I didn't cut my original plug. I just spliced into the wires and taped everything up but all original equipment is still there. The flasher from napa is a 3 wire plug. Signal, load, and intermittent light which could be a light on the dash or a buzzer. I only used the signal and load. You also will not need the ground wire from the original flasher.