Topic: 1975 CB750F - 10 volts for the headlight?

[sounddoc]

so the restoration is complete! still some minor adjustments and a new fender are needed, but both are on the way. something strange happened when i finally hooked all the electrics up today, though. the headlight fuse (7A - the marked spec) kept blowing each time i turned the headlight on. after a few times, the main fuse (15A) would blow too. so after much testing, i got an even 10 volts coming out the headlight connector - (high and low beams). the headlight had connectivity, too.....so what gives? sick of replacing 7A fuses, i decided to be daring and put a 10A fuse in there. the ohm-meter still had 10 volts of current at all RPMs. so i hooked up the light, went for a drive, and it's fine. so do i just have a different model fuse panel, or is something else going on here?

thanks!

[Mikeshonda750F]

You totally have a bad connection somewhere... BUT a voltage drop after the fueses is a fairly common occurance. 90% of the time, the fuse box is what causes the problem in the 1st place. Test your battery voltage on each side of the fuse and on each contact. Several times, due to a bad connection at the fuse, i would get a voltage drop across a fuse that would eventually blow the fuse. Next I would go over all the connections with some copper di-electric grease... but you can usually check the connections visually to see a bad connection. Look for what those in the biz call "greenies" or, bad connections that form a green oxidation inside a plug/socket/splice/ground/jumper/connection.

Also, try testing your voltages with the coils unplugged or the kill switch "OFF", this will stop the coils from constantly saturating and stop the points from welding themselves together... or in a worst case.. stop it from burning up your coils/killing the battery.. plus... they draw alot of current.

[sounddoc]

thanks! i'll try your suggestions. i did already check the battery voltage - with the bike completely off, i get about 11-11.5 volts across the terminals (the bike has been switched on a lot, and run for a few seconds at a time in the past 2 weeks, since i'm still in the process of bringing it back, so this is kind of expected.) but what confuses me is the 10 volts. the headlight seems to be OK with it when there's a 10A fuse, but 7As as prescribed blow immediately....but should i be seeing 12 across the headlight connector with a 7A fuse, instead of 10 volts with a 10A fuse? i always hated electrics, and i'm not all that knowledgeable with them. thankfully last summer when i was restoring my 550, the electrics were in good shape

-pete

[Dennis]

First (and simpler) things first! What is the voltage across the battery when running?
If it's not charging, you could see something like this. If it is charging, you've got a significant voltage loss. I would agree with the others in this case, start cleaning the connections, fuse box first!

[sounddoc]

i think i got it!.....i hope.....

I took off the fuse box, cleaned out the spider graveyard, and wd-40'd the connectors which were stained and some green. i put a 7a back in the headlight, which i had to steal from the tail light, turned the bike and light on and it didn't blow! now i just need another 7a to add to the rear light, and if all goes well, i think i got off pretty easy. Thanks all!!

PS - all three yellow AC leads from the alternator to a ground read ~14-15 volts while idling. not bad, eh? i'll get the battery terminals when i'm out next.

thanks again.