Jump to content
oliver2-44

Varying AC voltage burning out headlights

Recommended Posts

I'm having a problem with my 1985  312-8 burning out headlights due to the Ac voltage at the bulb varying.  I've gotten readings of 3,12,and 20 volts AC with the engine at normal running speed. On the DC side I am reading less than 1 volt.  I need some trouble shooting guidance

Share this post


Link to post
Share on other sites
 
 

The headlights should be DC voltage, NOT AC voltage.

 

Share this post


Link to post
Share on other sites
 

1985 312-8 has a 3 amp unregulated charging system.

 

One stator output goes directly to the light switch and supplies AC current to the lights. I can see how a failed bulb could result in higher AC voltage to the remaining bulbs.

 

The other stator has a diode in the wire next to harness connector and that one charges the battery. Peel the tape back and measure the AC voltage going into the diode. Notice the band on one end of the diode. A replacement must be installed the same way. A cheap 6 amp replacement diode should work.

 

For those with high battery voltage I recall SOI experimenting with this. He added diodes in series to reduce the output. Each diode drops the voltage about .6 of a volt so 4 in a series would drop the voltage .6 x 4 = 2.4 volts.

 

Garry

 

  • Like 3

Share this post


Link to post
Share on other sites
 

I suspect that you've already checked this but it could be the ground for the lights is flaky. The AC will vary with the rpm but shouldn't hit 20 volts. I had this happen on my 84 GT-1100. The charging systems are basically the same. The AC output was all over the place. I added a good ground directly to the lights and that solved the problem. :)

 

Oops! I overlooked the DC voltage reading that you stated. I would verify the ground first then go for the diode. That doesn't seem like it should cause the AC problem but maybe it could. :think:

Share this post


Link to post
Share on other sites
 

 

The tractor is at my sons house and last night we talked about running a separate ground wire. So thanks for verifying were on the right track. I ll report back after we do that. 

 

Jim G

  • Like 1

Share this post


Link to post
Share on other sites
 
13 hours ago, KC9KAS said:

The headlights should be DC voltage, NOT AC voltage.

 

After reading @gwest_ca post, I stand corrected!

Share this post


Link to post
Share on other sites
 

Easy mistake KC. I didn't re!alize it back when I was troubleshooting that GT-1100. The readings had me clawing my head because I was looking for DC. :)

Share this post


Link to post
Share on other sites
 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×