Headlight Dims With Fan

I don't know if this is normal but when the radiator fan comes on my headlights dim a lot. I just bought the bike (1994 VFR750) this week and noticed that the headlights were really bright sometimes and almost gone at others. When I got it home and killed the engine I noticed the lights dimmed again when the fan came on. So I'm assuming that's why they were dimming on the street. Is this normal? I checked the battery and its fully charged. The bike puts out a good 14.8 volts at 5000 rpm.

 

I have a 93 and I do not experience this issue. It sounds like there is an unsually big frain when the fan kicks on. Of course, when you turn off the engine and the key is still on, there will be a drain and the ligths will dim because there is no charge going to the battery. I am thinking three things, battery itself is going bad. How old is your battery? When, if ever, did you replace it last? Next, regulator/rectifier, which apears to be doing it's job since you have 14.8v at 5K RPM. I am not sure how to check but you also mig want to make sure it is putting out 5 - 9 Amps at 5000 RPM (referenced from my service manual). The last thing I am thinking is the stator. I would check all teh conectors for burnt wires and even posibly check the stator itself for birnt windings. If you do not have a service manual, I would suggest that it would be a good addition to your tool set. There could be soemthing else I am not thinking of. Maybe someone else on the list has an idea as well. And this is not to say that I am right. I could be off base in my logic. Good luck on finding what is causing the drain.

 

I have a 92' vfr750 and I had the same problem for a while. About a month or so after I noticed the dimming, my stater and regulator rectifier went out on me. I don't know if that was a tell tale sign of the electrical problems I was having but, after replacing the parts, I haven't had the dimming problems. You are naturally gonna get some dimming but, not the extreme that you're having. I hope this helps.

 

It might also be worthwhile to check for high resistance across the fan control circuit. A voltage drop test would reveal this.

With the fan running, check across the entire circuit, fuse to fan. If more than a .75V drop exists, narrow it by checking point to point - fuse to switch, across switch, switch to fan.

Don't forget to check for a voltage drop across the ground path, as well. High resistance = high current draw, especially when the fan first starts.

 

In my life, I've owned four Honda vehicles...two Accords, a Hawk GT, and a VFR... they all do this, or something like this. My VFR's headlights don't dim to a great extent when the fan kicks on, but it is noticable.

 

thanks everyone, I found the problem, there was corrosion on the plug coming from the fan where the faring connects. Now it only dims a little when the fan comes on.

 

actually i was wrong, that didn't seem to solve the problem and it does it randomly; not with the fan.

 

Check your connections on the headlight and the battery for corrosion. A little harder thing to do would be check the wiring running around and look for it grounding out somewhere. That would cause it to dim at random times.

 

The battery looks fine. I checked the chassis ground on the side of the frame and it looks fine too. It's not just the headlights but also the instrument panel lights too. maybe its the wiring in the upper fairing?

 

Turn the bike to on and sit on it move the handle bars around maybe rock it side to side a little and see if the lights dim. Wiggle some wires and see it happens. That is a good test to see if the wires are grounding. Intermediate electric problems are the worst thing to hunt down.