Wiring change to turn headlight off upon startup.

[dave brode]

Hello All,

Fwiw: My '02 FLHT with 95", 10.3-1 CR, SE 2521 cams is often a little angry on startup. AGM battery. Big cables.

I modified my wiring to cause the current to headlight to cut on start. I swear it made a big difference. Engine spins faster cold and hot, fires immediately with only 1 comp release open.

Dave

[Hossamania]

I had seen a discussion on this topic years ago, and it makes sense. One thing mentioned was to make sure the light comes back on quickly after starting to avoid overcharging, it sounds like you have this issue taken care of. Many manufactures set their bikes up to have this same startup feature from the factory.

[Coyote]

One thing mentioned was to make sure the light comes back on quickly after starting to avoid overcharging,

It has a voltage regulator to control charging independent of load.

[kd]

It is easier to accomplish with the old automotive 3 position ignition / starting switch.  There is no feed to the light circuit in the cranking position. That's all out the window when you have a separate start button. 

[Coyote]

A 10 amp SPDT relay connected inline to the head light and controlled by the starter solenoid wire will do it. Although I'm not sure why saving 5 amps would make much difference.

[kd]

Good point.  If it's that much difference cranking while using big cables the starter draw may be getting high or the timing a little too far advanced.

[smoserx1]

Terminal 87 of the starter relay feeds power to the starter solenoid when the relay is activated by the starter button.  There is another terminal 87A that is not used.  It is a normally closed terminal meaning it will turn off anything connected to it when the relay energizes, but keep it on otherwise.  You could run the headlight from it and that would accomplish your goal, but you would in effect now be powering the headlight off the ACC circuit instead of the IGN circuit.  Don't know if that is an issue for you or not.

[Don D]

Compression releases?

[jmorton10]

I solved that problem a few years ago by simply installing a toggle switch in the low beam wire.

I did that right after my regulator fried & the battery died before I could make it home.  If I could have killed the headlight that day, I could have made it home easily & saved having to call AAA for a flatbed.....

~John

[Dan89flstc]

If you need to turn off the headlight on an Evo or later model Harley to get enough amperage to the starter, you have a problem...

The few model bikes that were wired to shut off the headlight back in the `90s had a lot of issues with the dreaded click...

[dave brode]

Bottom post

Terminal 87 of the starter relay feeds power to the starter solenoid when the relay is activated by the starter button.  There is another terminal 87A that is not used.  It is a normally closed terminal meaning it will turn off anything connected to it when the relay energizes, but keep it on otherwise.  You could run the headlight from it and that would accomplish your goal, but you would in effect now be powering the headlight off the ACC circuit instead of the IGN circuit.  Don't know if that is an issue for you or not.

This is how I did it. I swapped the wires, no hacking. 87A normally feeds the radio, the interconnect side of the connector was empty on my FLHT. Easy, zero cost, easily reversed.

[dave brode]

If you need to turn off the headlight on an Evo or later model Harley to get enough amperage to the starter, you have a problem...

The few model bikes that were wired to shut off the headlight back in the `90s had a lot of issues with the dreaded click...

On low cranking pressure deals, I agree. Iirc, My '02 has a 30 amp headlight circuit, incandescent bulb.

I wish that i would have done this on my '99FXDL, 11.4-1 cr, TW9B cams, 118".

[dave brode]

Two replies:

Compression releases?

Yes, and required imo, at least after a 10 min hot soak. Maybe the "fix" treated a symptom rather than the cause, but either way, it is good.

Travel limiters set 1/2 turn up from bottomed. Lifter bleed down was an issue on my old 118" bike.

I will have CVO110 auto releases if I ever get the 120" engine that you helped me with done. [CVO 110 heads] 

---


KD wrote:

  If it's that much difference cranking while using big cables the starter draw may be getting high or the timing a little too far advanced.
KD

Canned map #4, no add'l initial adv.

Dave

[Dan89flstc]

If you need to turn off the headlight on an Evo or later model Harley to get enough amperage to the starter, you have a problem...

The few model bikes that were wired to shut off the headlight back in the `90s had a lot of issues with the dreaded click...

On low cranking pressure deals, I agree. Iirc, My '02 has a 30 amp headlight circuit, incandescent bulb.

I wish that i would have done this on my '99FXDL, 11.4-1 cr, TW9B cams, 118".

Lights circuit is 15A...

The headlight circuit is not drawing 30 amps, more like 5 amps.

[dave brode]

Dan89flstc said: Lights circuit is 15A...

You are correct - I stand corrected.

[Horizonmech]

Smoser is correct, this is an old fix, wire the headlight circuit into 87a at the starter relay AFTER the fuse box.....saves a few amp draw for starting. 

[smoserx1]

Smoser is correct, this is an old fix, wire the headlight circuit into 87a at the starter relay AFTER the fuse box.....saves a few amp draw for starting.

The only issue I see with that is the incoming high current wire for the starter relay (terminal 30) is supplied via the accessory circuit so if you wire it like that and actually use JUST the ACC position of the ignition switch the headlight is going to stay on all the time.  In the regular RUN position it won't matter unless you are worried about that extra 5 amps overloading your 15 amp fuse which might be a concern if you are using a high wattage accessory.  Now on a carbureted FLHT there is a rubber holder containing 2 relays (brake light and starter solenoid).  There is also a place on the right side of the frame you can install another rubber holder and add two more relays.  What I would probably do is install a third relay over there.  Ground new relay terminal 85 then splice into either 86 or 87 of the existing starter relay and connect this to 86 of the new one.  Then you can run your headlight wire into terminal 30 of the new relay and use 87A of the new relay to power the headlight.  I believe this is in effect what Coyote was talking about doing and it preserves the original wiring design.