TrögBlog – Volvo C306 Firetruck Restoration and Camper Conversion

Update on the cheezbrgr lights.   I had some flaky behaviour with the right turn signal not flashing when the running lights were on.  It flashes fine when they are off, and the left turn signal works fine.    The old Bosch mechanical flasher expects a certain current to flash.   Apparently, it’s right on the edge of oscillating, and (guessing) the internal switchmode power supply of the new cheezbrgers draws less flash current when the running lights are on.     The fix for this was relatively simple.   I added a 16 ohm 10 watt resistor from the flasher terminal to ground on the back of the cheezbrgr light.   I added a resistor to the left signal as well, even though it isn’t needed right now.

These 10 ohm resistors from Radio Shack will also work

http://www.radioshack.com/product/index.jsp?productId=2062291

For 24V systems, you want to use a 50 ohm resistor

http://www.radioshack.com/product/index.jsp?productId=2062292

The next problem was the interior dashboard indicator lamps failed to flash, even though the external lamps were fine.    This must be some sort of “dead bulb” detector in the Bosch flasher, for which the LEDs, even with the resistors, didn’t draw enough current.    It could be an inrush current thing.   Incandescnt bubls have a very low resistance when first turned on.  As the filament heats the resistance increases.

The fix was relatively easy.    I put each indicator lamp in the same circuit as the external flashers.    There are three three-way connectors behind the dash which distribute the flasher circuit.   They are the only three way connectors behind the dash.     On Trög one feeds two green wires, another feeds two red wires and a third feeds two yellow wires.    The yellow wires are the input to the flasher circuit (it unions the flasher and the hazard lights).   The other two, red and green ones are the ones you want to hijack.   For each of the red and green, I removed the female spade terminal from the feed wire to the three-way connector and crimped on a new connector to the old wire, along with a new wire.   That new wire was then fed to the indicator lamp.    On the electrical diagram I have, I connected the two three way connectors below Item 49 to Items 36 and 38 (red, green lines), and disconnected the original feed wires to 36 and 38 (orange slash).

It all works great now!

Another fix would be to source a modern electronic flasher which is pin-compatible with the old Bosch flasher.   I couldn’t find one in my searches and the surgery above wasn’t difficult at all.

wesc