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Engine quits when lights are turned on

Electrical issues
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HarryO
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Bikes: '55 FL
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Location: Port Huron, MI

Engine quits when lights are turned on

#1

Post by HarryO » Mon Oct 05, 2009 7:40 pm

The problem is on my '55 74 cu in pan 3 brush generator. My first mistake was to let someone else rebuilt my generator. After I installed it when the bike was running and the lights were turned on the engine would quit, blow fuse. The wire from the gen to the switch was grounded. I decided that the wiring in the gen was wrong and the marks telling me that what was what were not there. A friend and I removed the gen from his 45 eng and traced the wires and rewired mine and replaced the fuse with a circuit breaker. Now the bike will run a couple minutes before quitting, popping circuit breaker. I'm getting 7.2 from batt connection on relay until I turn on lights then it drops to 5.6. Although I've been do the mechanical work my bikes for quite a few years I'm not really up on the electrical system especially the 6 v on my pan. I don't really think it's anything big but my old brain is going in circles on this.



john HD
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Re: Engine quits when lights are turned on

#2

Post by john HD » Mon Oct 05, 2009 11:14 pm

harry,

first off welcome to the forum! good to see another midwesterner and a '55 owner to boot.

did the person who rebuilt your generator set it up to run as a 2 brush unit?

john

HarryO
Posts: 3
Joined: Sat Sep 26, 2009 12:58 pm
Bikes: '55 FL
'69 XLCH
'72 XL
'78 FXE
'74 ShoveSter
Location: Port Huron, MI

Re: Engine quits when lights are turned on

#3

Post by HarryO » Mon Oct 05, 2009 11:23 pm

No he rebuilt it as a three brush, but he had the wires from the winds going to the wrong places like wise with the brush wiring.....this caused the fuse blowing as soon as the lights were switched on because the green switch wire was grounded...

old52pan
Posts: 103
Joined: Thu Jan 29, 2009 8:14 pm
Bikes: 49 pan and a 52 pan project
Location: wisconsin

Re: Engine quits when lights are turned on

#4

Post by old52pan » Tue Oct 06, 2009 12:35 am

hmmm, all is fine until the ignition switch is moved over to the far right. I had a simular problem not long ago. replaced the ignition switch which was a newer aftermarket one with a original 56 HD unit and the relay which was doing nothing and viola. problem solved. oh ya and after checking I had the two wires on the generator reversed. :oops:

john HD
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Bikes: '42 WLA X 2, '55FL, '93 Ultra Classic, '91 Fatboy, '97 883, '71 Suzuki Duster 125, '83 GPz 750.

Re: Engine quits when lights are turned on

#5

Post by john HD » Tue Oct 06, 2009 12:46 am

HarryO wrote:No he rebuilt it as a three brush, but he had the wires from the winds going to the wrong places like wise with the brush wiring.....this caused the fuse blowing as soon as the lights were switched on because the green switch wire was grounded...

so all is good now?

john

FlatHeadSix
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Re: Engine quits when lights are turned on

#6

Post by FlatHeadSix » Tue Oct 06, 2009 12:51 am

Harry,
A 3-brush generator has 2 field coils; a "regulating" coil and a "shunt" coil. Both of the coils (windings as you call them) are different and they are independent of each other. The 2 terminal posts on the generator are "in" and "out" so to speak; the "RELAY" terminal is the "out" and the "SWITCH" terminal is for putting battery voltage INTO the generator to energize the shunt coil and create a magnetic field to boost the output. Both of the coil circuits are grounded by a brush, the regulating coil grounds through the 3rd brush and the shunt coil grounds through the 2nd, or "ground" brush.

If you get a dead short, or almost a dead short, when you turn the lights on you have a bad or incorrectly installed shunt coil. The field coils are sort of wrapped around the cast iron pole shoes which press them tightly against the inside of the generator case. If your rebuilder was not careful when he installed them he probably has pinched some of the coil windings between the shoe and the case, the thin wire in those coils was insulated with lacquer and then cloth wound. It is very easy to cause an internal short in those coils if you put them in the case wrong. Check the insulation on the terminal post first, if that is OK then disconnect the 2 leads going to the shunt coil, one from the brush and the other from the terminal post, and check the resistance in the coil itself with an ohm meter to make sure it does not have an internal short.

The rest of the wiring should look like the diagram below. Let us know what you find out.

good luck!

mike
Image

HarryO
Posts: 3
Joined: Sat Sep 26, 2009 12:58 pm
Bikes: '55 FL
'69 XLCH
'72 XL
'78 FXE
'74 ShoveSter
Location: Port Huron, MI

Re: Engine quits when lights are turned on

#7

Post by HarryO » Tue Oct 06, 2009 2:50 am

I want to thank you for suggestions....it's nice having so many minds working....
I replaced the switch and rewired the bike...I had removed the original wire harness before I came to the realized the short wasn't in the harness but in the gen....when I rewired I only wired for the necessity's....I checked out the dimmer switch and checked for shorts in the terminal in the front end......tomorrow I'm checking for shorts in the gen now that I know how to do that....Thanks

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