Topic: Running lights going dark below 1500 rpm, dash and flashing lights fine. What??

[RFogelsong]

I'm going to give lots of details (so, sorry for the novel below) because I can't figure out why all of my lights aren't going down, just the running light circuit.

My headlight and all running lights are going dim/completely dark below 1200-1500 rpm.  My dash lights are completely unaffected.  My turn flashers and brake light are completely unaffected, but my taillight, headlight (high and low) running lights (front turn signals wired up only), and gauge lights are all doing the same thing.

So what has changed?

What has changed was that I put on new rear turn signals

I ran them as just turn signals (not running lights, I left that lead disconnected) and everything was fine.  I decided I wanted them to be running lights and hooked the black wires into the taillight connector under the seat.  At this point I noticed the headlight was dimming (to a set level every time) whenever the rear brake light came on.  Similar to how you see headlights flash dim when people put their turn signals on sometimes.  It was still fine at idle and everything.  I figure I had feedback through a ground somewhere.

Before this, the headlight had never done this.  I was using the same brand turn signals previously, I just got new ones.   

I've since disconnected this wire so the rears are turn signals only.

Fast forward to two nights ago.  It was cold, my seat had frost on it in the morning (parked outside).

When I started it up that morning I noticed that whenever I had the idle below ~1500 the lights dim and at idle they cut out completely.  They flicker a bit at idle, indicative of current varying a little (cold idle so it wasn't perfectly smooth). 

Did my battery freeze overnight? What's going on here?  I know that the charging systems on these don't really "break even" until like >2000 rpm, but something's wrong here. All the cells are up to the correct marks in the battery.

Any suggestions?

[Fritz]

Looks like there quite some resistance in your headlights' circuit.
The first thing that I'd do is to check the fuse holder. Take out the fuses and clean the clamps. Maybe replace the fuses and try again.
Also, you must fully charge your battery before looking further into the problem.
It's a good idea to clean every single connector in your harness.
Since it's a time-consuming task, you could concentrate on the most important connections first:
- Wire harness to frame (green lead near coils)
- Battery to frame
- Ignition switch connector to wire harness
- Fuse holder
If you still have problems after doing them, go on with all the other connections...

[CycleRanger]

What has changed was that I put on new rear turn signals

The rear turn signals are not originally wired to be running lights. Only the fronts are.

[RFogelsong]

Okay, what I'm saying is that now I've got the stock wiring in effect and I have this problem.  I'll look into having the battery load tested and cleaning up all my contacts and report back.

[CycleRanger]

I would guess that the rear signals are not sufficiently grounded.

[RFogelsong]

So if the rears not being grounded is the problem (which it could be as I have them hanging on little painted ears now), would that mean that if I unplugged them and removed them from the circuit completely that I shouldn't have any more problems?  Because I tried that and it didn't make a difference. :/

[TwoTired]

So, you can feel around in the dark and play twenty questions, or you can hook up a voltmeter and note the voltages when the lights go dim.  Be sure to measure the mains black wire as well as the battery, and what voltage appears on the branch circuit of concern.

[Xnavylfr]

The charging system of the CB750 doesn't acually start charging until you get the revs up to about 2500-3000 RPM and it's not the most powerful system. It puts out just a little more juice than your lights and ignition systems demands from the battery. If you changed your T/S and tail light to LED bulbs you would find you wouldn't have as much of a DIMMING problem because LEDs use almost 0 power to work.


Xnavylfr(CHUCK)