View Full Version : headlight wiring connection question HELP !?!

Steve Swan
05-15-2016, 12:30 AM
I completed all my wiring on my 27, except for connecting the red, green and black wires to the headlight terminals.

i am uncertain what terminals on the bulb the red, green and black wires connect to. the headlight is from Poland, a reproduction 1927 grommet type. (having never seen the original connectors of an original headlight, where the 3 wires connect to, i'm not sure what to do and don't want to risk burning my $hit up.

i have posted 3 pictures, 1 of the headlight 1 of the wired switch panel underside and 1 of the red, green and black wires inside the headlight.

this Polish headlight, as you can see in the pictures, has a total of 4 terminals. 2 terminals connect to the main bulb. another terminal is ground. the 4th terminal is for a parking lamp. (did 1927 headlight have a parking lamp?)

i fitted a new high quality wiring harness from Bob Luland.

Looking at the 1927 Rider's Handbook:

A. i have connected the black main harnes (tail lamp) wire and the red headlight wire to the #3 switch panel terminal.
B. i have connect both the green and the black headlight wires to the to the #4 switch panel terminal

i am thrown off by the green and black wires both being connected to the #4 terminal and leading to headlight. also, i have noted the very clear comment on page 23 of the Handbook, "Switch box must be securely clamped to fork triple clamp, for it requires a ground. If the switch box is not grounded, the large bulb in the headlight cannot be lighted." Does switch box ground to frame by nature of being held by to bolts against triple clamp ? it seems none of these 3 (red, green, black) wires are a ground wire.... ?

so... my question is: "What terminals on the headlight do each of these 3 wires connect to?"

Thanks in advance for your help (:


steve swan

05-15-2016, 01:33 AM
Hi Steve, looks like you are doing another late shift!

Re the wiring, I usually find it very helpful to use a meter to bell out all of the various wires and switches and then sketch out the wiring. Its a 1927 motorcycle so it should be dead simple.

Unfortunately my bike is the magneto model so it didnít have an electric headlight.


Steve Swan
05-15-2016, 03:34 AM
Thanks John !

02-26-2018, 08:35 PM
Hi Steve:

I am about to cross the same bridge you did with the headlight wiring. I am wiring a 27 JD. I too have the reproduction headlight and have the same question about the red, green and black wires. What did you determine?


02-26-2018, 11:06 PM
The HD riders handbooks have wiring diagrams in them.
I've attached the one for 1926 and the one that covers the 1927 and 1928 bikes.
If you can get hold of a copy of the appropriate Riders Handbook for your model get it and it will be well worth your while.
You will find they answer a lot of the questions posted on this site.

02-26-2018, 11:46 PM
Something worth pointing out is if you study the wiring diagrams you will see that Harley always hooked the earth wire of the battery up through the ammeter if one was fitted.
That's fine on all J models up to 1928 as the ammeter was screwed to the main frame rail so everything got a good earth.
When the 1929 models came out with the ammeter in the dash that was mounted on the handlebars it was a different situation.
The earth now had to get back to the main frame via the front fork head stock bearings and if these were properly greased total earthing became a bit of a problem.
This problem existed until the dash was again mounted onto the top frame rail.
All sorts of little electrical problems can occur because of this and can be a swine to find but generally if you put a jumper lead from the forks to the frame they all go away.
Because of this when wiring any of these Harleys I always put an extra earth wire in my loom and this positively connects the forks to the frame.
Done right nobody will know its there and it solves a lot of electrical problems.
I've attached a 1929- 1930 wiring diagram,
Sorry if I've dragged this off subject but I felt it was something worth making people aware of.

Steve Swan
02-27-2018, 11:43 AM
Hello Bob

i just now saw your question. as you know, my bike is a 27 model, but unless i am wrong, 26-28 wiring is the same. i am running a Polish headlight and switch panel. i also have ammeter fitted.

First, i would suggest reading Tommo's words and following his lead.

as to how i wired my headlight, visualize the switch panel installed on the bike.

the red wire leading from the headlight attaches to upper RH (#3) post of switch panel.

the green wire leading from the headlight attaches to lower RH (#4) post of switch panel.

i ran the black wire from the headlight directly to ground on frame, using the upper screw of the LH control coil clamp as the attachment point.

the reason i ran the ground wire to where i did is because i wanted the shortest length of ground wire possible, instead of (if i understand correctly) running the black wire from the headlight to the negative terminal on the ammeter.

i hope this helps. if anyone notices where i may be wrong, please advise accordingly.