Eldorado Loses all Electrical power when headlight retaining screw is turned in

[850Fool]

Essentially stock '74 Eldorado except for the addition of relays to power lights.  Bike running fine.  Horn hasn't really worked since I've owned it.  Finally got around to looking into the problem.  Opened up headlight bucket, but otherwise disturbed nothing, just took some photos to plan fix to include adding a micro relay.  Closed up the bucket.  Turned on the ignition key and the panel lights didn't come on.  Headlights, signals and starter appeared to have no power.  As I reopened the bucket, everything came back on.  When I screwed the headlight retaining screw back in, I reached a point where the lights would go out again.  I did this several times and the bike would run fine as long as the screw was not in all the way.  Headlight plug is not mashing anything, fuses look fine, contacts are clean.  Does anyone have an idea what's happening?    :Beating_A_Dead_Hors e_by_liviu
Thanks for any insight!

[fotoguzzi]

What happens if you unplug headlight and put screw in?

[Antietam Classic Cycle]

Sure sounds like the headlight is pushing a fuse out of place or straining a wire causing an open connection. 

[Kiwi_Roy]

It's about to melt down, sell it to me cheap.

Those old fuse blocks have seen better days, one easy fix for loose fuses id to stretch an "O" ring around the clips to add more tension, polish the ends of the fuses by rubbing them on your pants first, smear with a bit of Vaseline then add the rings. I think the terminals work loose as well, I fitted the blade type to mine but it's wired completely differently with the fuses in the battery box.

[Tom H]

 :1:
and
 :1:

Try pushing in on the wires behind the headlight with the headlight out, you'll most likely find a fuse not making good contact. Been there, done that.

Tom

[JoeW]

Does it have an H4 headlamp in it? If so, that's the problem it extends too deep into the bucket and touches the fuses.

[Kiwi_Roy]

Here's the schematic from the Owners Manual.
I strongly recommend adding a main fuse at the battery, this doesn't really alter the original wiring in any way just use an in-line fuse fed from the battery and bolt the original 2 wires to a lug
This fuse should never ever blow but if it does you've protected your investment from the batteries 200 odd Amps
This applies to any of the older Guzzis with unfused wiring

[Antietam Classic Cycle]

Does it have an H4 headlamp in it? If so, that's the problem it extends too deep into the bucket and touches the fuses.

If you do a little searching, you can find H4s that aren't too deep. I'm running an "Autopal" cheapy in "Barney" and it *just* clears without knocking anything loose. Bosch or Hella did make one too that was shallow enough. 

[normzone]

A trick my dad showed me on my Eldo fusebox - feel around on it. If there's an area where there's poor contact, it may be warmer there as the current attempts to bridge the gap.

[850Fool]

Thanks for the replies!

FotoGuzzi and Tom – Duh… brilliant!  Because I couldn’t feel any mashing putting the headlight back in, I was so focused on what could be bumped to cause a complete blackout that I ignored the possible bumpor (headlight connector).

Kiwi Roy – Can’t sell it cheap.  I bought it with chrome already added to the oil.  Mark Etheridge rebuilt engine from the ground up and went thru the tranny/final drive components.  Awesome job and well worth it.

Kiwi Roy and Charlie – I suspected loose connections and went through each one.  The bullet connectors all seemed tight to the wires and into the busses, no corrosion but used electrical grease on re-attachment.  The fuses were the same, clean and corrosion free, except I could spin a couple fairly easily by hand.  I wasn’t too concerned as these were either connecting nothing or were circuits that seemed to feed off the main and could not by themselves cause the total blackout.  I could not see well behind the fuse panel and busses, and didn’t want to make a simple problem worse.  One thing did surprise me.  I let go of the red main coming into the top of the fuse panel while cleaning it and it touched the headlight bucket.  Snap, crackle, pop!  No smoke got out of wire anywhere (I hope).  Based on the wiring diagram, I thought with the ignition off, there couldn’t be any power to stuff in the headlight bucket.  Still don’t know how, but Hello 40A fuse!

Joe – I believe the headlamp is an H-4, it does seem a little deep and I can still see the brass tabs with the connector fully engaged.  As Charlie suggested, there may be a more shallow bulb in the very near future.  I could ditch the connector, bend the tabs, and wire in single connectors, but that is a bit too tacky at this point…

normzone – Also a great idea I hadn’t considered.  This may come in handy if I really have to dig deeper into the connections before replacing everything.  I happen to have a Harbor Fright laser temp gun that might make it even easier and less painful. 

Okay.  The headlight screw needs to go in another quarter inch to be fully seated.  Based on all your suggestions, the plan is:
   remove the headlight and reattach the retaining ring, running the screw in fully
   with panel lights on, wiggle wires, connectors and fuse
   if lights go out, affect any repairs
   using a clean wadded up rag, gently press the fuse panel where the headlight could be hitting
   if lights go out, get a more shallow bulb, or perhaps trim the tabs on the existing bulb so connector
      fully seats as a test
   clean, apply electrical grease to all fuse connections
   if none of this works, plan B is Greg Bender’s website, Waytek mod, etc.
   install 40A fuse from battery

Thanks for the help, all!!  I’ll post again when I’m done.
The horn works now!  I don’t use it, but required by CA law…

[mtiberio]

your title made me laugh. thanks...

[Tom H]

The part of pushing on the fuse panel, not so much the panel as the cluster of wires in front of and that attach to the panel. If pushing on them makes a change, then it's narrowed down. Sometimes it takes moving them side to side. I guess I'm trying to say wiggle them a bit until you find the light goes out then narrow it from there.

Also, look for a chaffed wire.

As far as changing the headlight, it may just be a matter of moving the wires a bit that are behind it and it should work fine.

Good luck,
Tom

[850Fool]

Checked the connections with the headlight out.  All wires and fuses were clean and firmly in place.  I found the center fuse (from the starter button) could be popped up out of its holder (not knocked completely out of the holder) by the headlight connector, just enough to interrupt the power.  I polished the fuses and contacts, applied dielectric grease, and put 7/16 ID O-rings on the fuse holders.  Took the Wagner H6024 headlight to O’Reilly’s and compared it to a Sylvania H6024.  The Sylvania was about a half inch shorter in profile (lower wattage so I may look for another).  I swapped it out and everything works with the retaining ring screw run in fully.  Freakin’ Eureka!  Still have to hit the road, but I think problem solved.  Thanks for the help!  Now on to fusing the battery.   

[Tom H]

Congrats

Tom