[VAC] Re: ail lights

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

Chasing down marker lights on my Caravel last summer that didn't light
(essentially all of them) I found their problem was universally bad
grounding of the fixture. The ground depended on the pop rivet
compressing plastic. I rebuilt all with solid aluminum screws, with the
screw heads inside (had to cut keyholes to put them in), lock washer and
aluminum nut to anchor the bolt to the Airstream skin, then another nut
to be a spacer (I drilled away the plastic post of the original Grote
fixture), then put another lock washer and nut on the outside. I applied
aluminum conductor dope to all the connections along with stainless
steel shake proof lock washers. The last I checked, I could see the
markers in bright sun. The back up lights will probably be helped by
some of the same techniques, especially since mine seem to be
intermittent.

LEDs do inherently run on lower than 12 volts and need some sort of
current regulator or series resistor to control the current they draw.
Low currents on plain brass lamp sockets could be another problem with
lamp socket corrosion.

It can take considerable attention to details like connections, wire
sizes, and grounding to achieve full brightness lamps on the tow vehicle
or the trailer, made worse by wire sizes sometimes chosen for wire
economy than voltage drop. I'm thinking that connections should coated
with silicone grease to keep corrosion out. Especially lamp bases. I'm
using one from Ford specified for their truck lamps. The aluminum
conductor grease may also be good for copper connections but since it
has metal powder as filler, I don't think its appropriate for lamp bases
when it might bridge insulation.

Using relays an the trailer battery could achieve brighter trailer
signals at the cost of complexity and complexity always leads to lower
reliability. Getting full voltage on the lamps also means they won't
last forever since incandescent lamp life is cut in half for each 5% the
applied voltage rises.

Gerald J.