Packard Forum Index » Project Blogs

To flash properly, the original TungSol thermal flashers are dependent on having the resistance they are designed to work with in the turn signal circuit. With the original flasher, are the outside lights still working? Did you change to LED bulbs anywhere within the turn signal circuit? Usually a single flash on the indicator means one of the outside bulbs is not working. If the outsides still work, then there is a possibility the flasher is not functioning in both sections. If you have gone to LED bulbs you will most likely need to add resistance in the circuit at the bulbs or go to a different flasher -- either an all electronic flasher which has a stable repeating internal timer circuit working a relay for the power out to lights or a flasher specifically designed to work with LEDs.

The reason for the opposite side grounding in a dual indicator circuit is that the flasher only outputs one feed (terminal P) which goes to both indicator bulbs at the same time. With a regular or normal bulb ground method, both indicators would flash at the same time no matter which side was selected. By grounding thru the wiring to opposite sides, the indicator bulb for the side that is flashing will see voltage at one leg from the flasher and be able to find ground by effectively going in series thru the bulb filament of the dead side so it will light. The indicator you do not want to light will see the same voltage on both legs -- from the flasher on one and from the working outside bulbs on the other so it will not be able to light.

As mentioned in the other post, the 535 has a transistor which works the indicators and being a PNP transistor, it is the wrong polarity to work in a positive ground circuit. Change it to a NPN transistor with comparable current specs and the flasher will work with a positive ground. Modern cars or cars with only a 2 terminal flasher have the indicator bulbs in parallel with the outside lights and socket grounded so indicators light at the same time as the outside lights.

Here is a comparison between a typical TungSol flasher (47 version shown) and the 535.

Thanks Howard. I'm not using any LEDs at this point, just the normal 6 volt bulbs. The outsides still work, though I'm still getting a random intermittent failure on the front passenger. It appears to be at the connection from the wire loom to the back of the bulb socket (jiggling the wires causes it to work). I pulled the bulb out at lunch today and applied some dielectric grease to the bulb contacts and ground, assuming it was a poor connection at the bulb. I had cleaned the bulb and socket contacts previously. So far it is working.

Should I go through all the grounds again? Maybe the TungSol is not seeing the resistance that it's used to because of bad grounding. I just find it odd that the indicators flash once, then no more.

I've had the TungSol open before when I was trying to diagnose this and other problems, but I didn't see anything that seemed to be a problem.

Maybe I need to open the 535 and see about swapping the transistor?

Going thru grounds again definitely won't hurt. Several have even had to resort to adding a ground wire directly from the body to the front park light housing and sockets because of all the issues trying to get a good reliable ground thru the many corroded pot metal grill and body connections. Rear grounds are usually not as much problem but some have gone all out and added a wire there too.

If you want to change the transistor, here is the transistor another poster says works.




Amazon has the 123ap transistor but is asking what I think is a ridiculous price. They are cheaper on ebay.




Didn't want the bother on mine so didn't try changing it. For only a bit more than a transistor would cost and a flasher that can take more or varied type bulbs, I just bought a positive ground electronic flasher because they are less fussy and generally less trouble overall. They are polarity and voltage sensitive though so do take care not to accidentally reverse the battery or, since they will be powered any time the ign switch is on, try to jump a dead car with a 12v battery.