I need some help making my tail light work on my 80 ironhead. Electrical is my weakest area so it may be something simple.

I installed a new side tail light/license plate holder. wired it up and it did not work. I am pretty sure it was working with the old stock light.

the light has 2 wires coming out the back, one red and one green, the red goes directly to the brake light switch then up to a relay and then on to an ignition switch

the green goes to another relay then off to the ignition switch

if i put test leads from +/- battery to the two wires coming out the taillight it lights up

if green is hooked up to the bike and i jump red to + battery it lights up

if both are hooked up to the bike and i jump + battery to the green, the head light comes on but no tail light

if i skip the brake light switch by putting th 2 wires going to it directly togehter there is no change

i have a multi meter and test leads but not sure how to properly use them here

 

From what you're describing, it sounds like you might not have the new side/taillight assembly grounded properly. The tail/brake light assembly is grounded through its mounting bolts. If it's not grounded, no current will flow through the bulbs.

It sounds like you do have it wired up correctly. The red wire is for the brake light, and the green wire is for the taillight. What you're calling "relays" are actually circuit breakers.

To check to see if it's a grounding problem, connect a wire from one of the taillight mounting bolts to a good ground (or the negative terminal of the battery) and see if it works correctly then.

If it's not a grounding problem, use your multimeter to troubleshoot. Your meter should have a black lead and a red lead. Plug the black lead into the "COM" jack, and the red lead in the jack for reading voltage, ohms, etc. (You don't want the red lead in the "Amps" jack, since you'll be measuring voltage, not amperage.) Set the meter to read "DC volts".

Clamp the other end of the black meter lead to a good ground somewhere on the bike. Touch the end of the red meter lead to the green wire and turn on the ignition switch and turn on the lights. Your meter should read close to +12 volts at the green wire, and the tail light should light up.

Touch the red lead to the red wire and apply the brakes using either the rear brake or the front brake. Your meter should show the same +12 volts and the brake light should light up.

 

yep he hit it the ground

 

great thanks

i am working alot the next couple days but will give it a try as soon as i get a chance

 

works perfectly fine with a good ground
i just figured it was grounded by mounting directly to the swing arm, but i guess not

thanks for the advise

 

Good to hear it's working. Thanks for letting us know how it turned out.