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1990 FLSTC head & passing lights burning out

islandtikiman

islandtikiman

Member
I really am stumped on this one. I am riding along just fine and all of a sudden the motor starts to backfire & loose all power. I pull over to the side of the road & it's idling just smooth as a baby. I then continue on without another problem. However, I now have ZERO head and passing lights. They are toast! all filaments have been blown! The turn lights, fender lights & stop light are fine. I replace all of the blown lights with new bulbs (not cheap!) and a couple weeks later the same thing happens again. All lights blown.

These are the conditions when this happens:

1. I'm on the highway going 60-70 mph. It has only happened at these speeds. Never at street speeds.
2. I have been going that speed for anywhere from 5 to 15 min. before the event happens.
3. When the event happens, the motor sounds like it has blown a head gasket at speed but is just fine by the time I stop the bike.

I don't think the problem is a short because that would not blow a bulb. I'm thinking it could be a voltage regulator, however, why didn't it blow ALL of the bulbs if it was that?

I really need some help here. If anyone has any ideas, please let me know. To keep buying new bulbs ($20.00+) is not an option!
 
I would have to go with the voltage regulator.

You may want to hook up a volt meter so you can verify what the voltage is should it happen again. It would be the best way without just throwing parts at the bike.

At the 60-70 MPH / 3000 RPM's is about when the charging system would be putting out a good charge and this is when a spike in output would blow the bulbs.

Also check the ground connections like the regulator itself as well as the ground cables on the battery.

I would also replace the main breaker first. There were problems with them in the early 90's and around that year.
 
Thanks for the quick reply Glider. I guess that is what I should do, however, I will need to think about how to but a multimeter onboard.
 
You could just hard wire a cheap volt meter (VOM) like radio shack and tape it to the bars for a temp check on the voltage when this happens.
 
I hooked my multimeter up to the passing light positive wire and it reads 13.4 volts at idle, however, when I rev it up faster (don't have a tach so I don't know what the revs are) it goes to almost 18 volts. I hold a steady rpm at something above idle and it does a steady climb up to over 17 .5 volts. The regulator is supposed to limit the voltage between 13.8 & 15 volts. It seems a bit unstable to me because of the climb in voltage.

My question then is this difference in voltage going to blow the head light & passing lights and not the other lights? I know that any high temp bulb is very fragile and that small difference could do it. Also, the voltage may spike even more at the problem speed. Anyone have an opinion?
 
Looks like a bad regulator. 18 volts is way to high, you shouldn't see more than about 14.5 at best.

In regards to the lights blowing, it seems all the higher watt lights are the ones blowing, more than rated volts and more heat could be doing it.

Check the electrolyte in the battery is it isn't a sealed one. The high charging rate can and will cook the battery away causing low levels of electrolyte.

Check over the regulator using this procedure.

Testing The Charging System - Harley Davidson Community
 
Thanks for the help Glider. I'll replace the regulator and post the results. The one thing that I'm still confused about is the engine miss-firing and loss of power when the event happens. Could the over voltage be causing the ignition module to go crazy?
 
Over voltage is as bad as low voltage. The sensors and parts are designed to work in a certain range such as 5 volts for most and if they are higher, they send the wrong signal to the ECM, so it's possible for the ECM to get confused with the incorrect input.
 
Well, the problem was the voltage regulator! I installed a new one (HD ie:Hundred Dollars!) and did voltage tests before I installed the new bulb. It came up to a tad over 14 volts no matter how high I reved the evo. I installed the new head light bulb and went for a ride. Got back home and it was still shinning bright as new!

Thanks Glider for your input. This is my last post to this thread. Ride on brothers.....
 
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