electrical expert

[photobug]

In need of someone that has a bit more electrical knowledge than I do. I'm trying to attach an extra brake light to my bike rack that hooks up to the trailer hitch using the trailer hitch wiring. Thought I had it figured out until I tried it. Went to try the turn signals and both sides on the coach blinked. disconnected hitch wires and turn signals went back to normal. My thought are since both sides are connected in the light on the bike rack, it's running power back through the side that isn't being used. What I probably need is a couple of diodes to prevent reverse flow on both turn signal lights. Here's where I need the help. How do I determine what kind/size/rating diode to use? I know the theory, just never had to use any in a project that wasn't already pre set up for me.

[Bobbo]

Much easier to just install another one of these



at the rear of the coach/car (or on the bike carrier) and only tap into the "STOP" and "GROUND" wires. Doing this would let you use the 4 pin or 7 pin hitch connector. At 4"x9" it is fairly large, but at $22 it is cheap and easy. (Clicking the photo above loads the Amazon.com page.)

[wnjj]

Bobbo wrote:

DrewE wrote:
The bike rack light will flash whenever a turn signal is on and the brakes are applied, though.

True. We are back to tapping the 3rd brake light wire or the output wire of the adapter.

It can be done right with 2 relays and 3 diodes but that's getting pretty complicated.

[Bobbo]

DrewE wrote:
The bike rack light will flash whenever a turn signal is on and the brakes are applied, though.

True. We are back to tapping the 3rd brake light wire or the output wire of the adapter.

[DrewE]

Bobbo wrote:

wnjj wrote:
How about a relay which is controlled by the left turn signal? Then feed the right turn signal through to relay to your 3rd brake light. Then it will only light when both lights are on. A solid state relay would be best since it will cycle quite a bit.

This is a wonderful idea. One of the turn signal/brake lights activates the relay, but sends no power to the new light. The other turn signal/brake light sends power to the new light, but if the relay is not activated the power does not get there. The third light will ONLY light up if BOTH turn signal/brake lights are lit.

The bike rack light will flash whenever a turn signal is on and the brakes are applied, though.

Frankly, if it is not too bright of a light, I'd be tempted to hook it up to the running/tail light circuit and have it on all the time the headlights or parking lights are on. If it's more bright like a stoplight than a tail light, that's probably not a good solution. I don't know about the precise legality of such a setup, but I suspect it's close enough to being legal to not get into too much trouble.

[Bobbo]

wnjj wrote:
How about a relay which is controlled by the left turn signal? Then feed the right turn signal through to relay to your 3rd brake light. Then it will only light when both lights are on. A solid state relay would be best since it will cycle quite a bit.

This is a wonderful idea. One of the turn signal/brake lights activates the relay, but sends no power to the new light. The other turn signal/brake light sends power to the new light, but if the relay is not activated the power does not get there. The third light will ONLY light up if BOTH turn signal/brake lights are lit.

On the relay, attach pins 85 and 86 to the hot wire of one of the turn signal/brake lights and a vehicle ground. It does not matter which pin goes to which point.

Attach pins 30 and 87 to the other turn signal/brake light hot wire and the hot wire of the new light. It does not matter which pin goes to which point.

Do not use pin 87a.

[wnjj]

Using diodes means the new light will flash if either turn signal is on. Not a good idea and may not be legal. Turn signals are supposed to indicate direction which a center-mounted light will not do.

[MEXICOWANDERER]

Diodes. Go overkill city.

For something like this I will choose a 10 amp axial diode. I use heat shrink on each side but leave the plastic diode case exposed to lose heat. Twin 6-amp axial diodes can be used in parallel each side but that's a little lumpy.

Yet another area where theory gets the ---- knocked out of it by reality. When I used 3-6 amp 1,000 PIV rectifiers on a 2 amp incandescent bulb they failed. Theorists fail to acknowledge tungesten filament inrush.

[wnjj]

photobug wrote:
I'll have to look into how I would wire a relay, especially since I have a relay that the support tab snapped off, also still have the old turn signal relay I replaced to fix the hyperflash issue when I switched to LED lights.

12V automotive relays have pins with numbers in the 80's, plus 30.

Pin 85 - ground on 7-way
Pin 86 - left turn on 7-way
Pin 30 - right turn 7-way
Pin 87 - first pin of new light
Ground on 7-way - other pin of new light

This performs a logical AND which only lights the new light if both left turn AND right turn are lit. Your turn signal unit is probably a flasher and not the same thing as a relay.

[wa8yxm]

Your thinking is good. Two options, well 3
One, you can get an adapter, kind of like the one pictured above. Been a long time since I've seen 'em though they will turn on the added light ONLY if both turn signals light.

Option 2 is to go to a dual lamp system on the bike rack, one for each side. This way half the fixture lights if it is turn signal, all for brakes,, I kind of like this solution, Or two side by side single lights.

Finally diodes.. Put diodes (3 amp at 24 volt should do nicely) from your local electronics store in the line.

Diodes are electrical "Check valves' put it in but do not formalize (Solder) the leads and test, if it works the way you want great.. Oh the banded end goes toward the bike rack. (if the diode is backwards turn it around).

[photobug]

I'll have to look into how I would wire a relay, especially since I have a relay that the support tab snapped off, also still have the old turn signal relay I replaced to fix the hyperflash issue when I switched to LED lights.

[wnjj]

How about a relay which is controlled by the left turn signal? Then feed the right turn signal through to relay to your 3rd brake light. Then it will only light when both lights are on. A solid state relay would be best since it will cycle quite a bit.

[photobug]

I actually installed the 3rd brake light on the coach myself using the controller bobo shows. That controller is about 4" x 4" x about 1" thick. Too big to fit on the bike rack. I suppose I could tap into that to control the bike rack light. Problem is, I use the rack on both my cars as well. I don't really mind that the light blinks if only the blinker is on as long as the turn signals work like they're supposed to. I just want it to be visible so someone doesn't run into them. With the trailer hitch plug, the light bar lights up dim when the driving lights are on.

[azrving]

My adapter is the opposite of Bobo. His is more of what you are looking for.

[azrving]

LittleBill wrote:
shouldn't need an adapter. simply tie into only 1 turn signal light.

Then it flashes as a turn signal too but only for one side. It seems that he wants it to be a brake light only