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What to do when your actual fuse panel doesn't match the diagram?

Started by michaeld, 16 February 2006, 10:08 PM

michaeld

Hey all,
I've been tinkering w/ my electrical system and was advised (by John Hubertz, I think) to replace the fuses.  They appear to be the newer type, and look fine, but I've decided to replace them anyway (and clean the panel contacts). 
Anyway, I have a slight dilemma: two of the fuses in my 77 450 sel don't jive with the diagram, specifically #1 (diagram says 8A; clock, trunk/roof/hazard/standing lights, antenna, warning buzzer) and #3 (16A; air conditioning).  In my box presently #1 is 16A and #3 is 25A - higher than called for.
For the #1, I'm inclined to replace w/ an 8A and see what happens, but #3 is a bit of a mystery to me: someone wiser than I in the ancient mystical art of auto electronics has at some point welded an in-line 25A glass fuse into the #3 fuse in addition to the ceramic 25A. 
Has anyone encountered such an arrangement?  I have conflicting inclinations: My first inclination would be to stay same-same with the electronic-jedi who worked on the system, and my second is to never ever have a higher rated fuse than the system is supposed to have.  What do y'all think?

John Hubertz

If it isn't broken, don't fix it.  You can use a process of elimination to determine the modifed circuits - and many of these 116 fuseboxes were modified to reduce or eliminate the electrical gremlins that occur.

Often you find radio installers rewire to allow a separate fuse to carry "clean" power and eliminate radio hum, a problem on all Benz with the early electronic ignition.  The spark on these cars will kill a mule.

John
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

michaeld

Thanks for the reply, John,
I've had 2 complaints about my 450 sel: fuel efficiency and secondary electrical systems.  I can't do much about the former, but the latter, I can improve (or make worse!). 
I'm going to leave the 25A fuse on #3 (that handles the AC), but make #1 spec and replace it w/ an 8A, and see what happens.  Actually, I don't know HOW I would go about determining if that #1 circuit was modiefied; the only process I know of is to replace the fuses and see what happens.  If it blows, then I'll have found one of your gremlins. 

John Hubertz

My bet is that the extra fuse goes somewhere like a radio or an old CB Radio that may or may not still exist.... 

More importantly - increasing the size could be the previous owner either ran out of the original amperage fuses or possibly excess load.  The heater fans pull a lot of juice when they begin to fail, and the antenna circuits are notorious because OEM antennas are so prone to internal rust.  I'd check the "pull" on both these circuits and you may find your culprit isn't the fuse block but rather the age of the load (actuator motor/fan motor) and then you have some deciding to do.

J
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

oscar

I might just throw a quick thanks John for this bit:
Quote from: John Hubertz on 17 February 2006, 08:01 PM
Often you find radio installers rewire to allow a separate fuse to carry "clean" power and eliminate radio hum, a problem on all Benz with the early electronic ignition.  The spark on these cars will kill a mule.

That explains a lot re my original crappy AWA AM radio.  Tried putting in a cheap FM unit ages ago as an interim replacement, not only did it lose memory and time because of no constant power once the ignition key was removed, but the reception was crappy even though the antenna was fine.  Both units exhibit static.

I plan to get a Becker unit and use my ipod, looks like "clean" power should address the interference.
1973 350SE, my first & fave

michaeld

Hi all,
Well, John's words, "if it aint broke..." really resonated with me.  I'm the kind of guy - mechanically speaking - who (with a lot of groans and stifled curses) is generally able to take off a broke part and put a new one on in its place.  After that, my limitations begin to quickly surface.
I've started to read up on auto electric, and it's really facinating stuff.  But I'm not at the point where I know how to test the "pull" of a circuit (I've got a volt meter, I just don't know how to make fill use of the darn thing yet).  It seems wise to begin to learn about auto electric if you have an old car and you aren't made out of $.
Anyway, the original owner was a doctor who liked his creature comforts, judging by his service records.  Every few years, the climate control system would break down, and he spent a couple grand to fix it half a dozen times.  He also installed a quality aftermarket stereo system.  To be honest with you, I don't know if the #1 fuse in the panel was utilized for the stereo or not, so I replaced it with the same amp fuse that was in place (16A) when I went in and replaced all the fuses.  I also replaced the 25A fuse in the #3 slot w/ same.  I figured it was either a mistake, or someone knew what they were doing.  I'll come back and take another look at those two fuses when I have a better sense of what I'm doing.
Sadly, all the work I did (replacing my ground strap and adding a new ground strap, replacing the negative battery cable w/ a 2-piece system from neg to alternator and from neg to sheet metal, adding a ground wire from engine to firewall, and replacing all my fuses) did not seem to drive away any of my gremlins.  I still have 1) a radio and antenna, 2) shift knob light, 3) rear door window that intermittantly work and then stop working.  I'd sure like to know how to fix them varmint gremlins, but I chalk up my efforts to routine maintenance.  I'd also have added a ground wire to my instrument panel, but I frankly didn't know the best way to access the firewall from the interior.  Any help on busting my gremlins would still be appreciated.  Thank the good Lord, my problems are on minor secondary systems, and everything else is peachy dandy.  I'm starting to think that maybe I got my $800 worth when I bought this car!
Mike

John Hubertz

I can't speak to the radio and antenna, but the switch is the known culprit on the window.  Call Burgess at T-Wiley in memphis and he'll mail you a few for very little $$$  I wish I'd known of your need or i'd have had my chicago friend pull switches before he junked his.

I've got an antenna switch that works perfectly if you want to try that.  Toss a $10 in an envelope and send it to:

John Hubertz
2816 Palisade
Fort Wayne, IN  46806

I also have an 86,000 mile ac/heat control head if you know anyone who needs it.

John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

John Hubertz

Hey - one more thing michael - run a big old jumper wire straight from the hot terminal of the battery to the fuse block for the evil window....  if it solves your problem it is either the relay or the power feed.

Do the same for the radio feed....   

Keep us posted!~  gremlins are best chased when well identified by fellow hunters!
John Hubertz
"When the going gets weird, the weird turn pro."
(Hunter S. Thompson) 

1977 450SEL (Max Headroom)
[img width=68 height=73][url="http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg"]http://i48.photobucket.com/albums/f248/fullhappyfish/max.jpg[/url][/img]

michaeld

John,
That's right!  Let's gang up on those little rat bastards!  They won't know what hit them if we come at 'em from all directions with our big mallets.
You gave very good advice, but I want to make sure I understand correctly: are you saying to run a bypass/jumper wire from the pos battery to the fuse panel (specifically, the #16 fuse, rear right window)?  I've got 10 gauge wire and some alligator clips; is that all I need to hunt gremlins?  Or will they just laugh at my pathetic armament and slap me silly?

My antenna has generally worked for me; it has only quit once for a short while.  My radio has been more sporadic, but even it has worked most of the time.  It's been the window that has pretty much said, "I think I'll take the next two weeks off" to me.  You think it's the switch?  The funny thing is I don't even really need the rear window; it just irritates me that it doesn't work.  It mocks me back there, and I'm powerless to show it who's boss.

btw, I was all the more worshipful in church this morning because my right rear window worked (I try it when I get bored just to see what happens).  Maybe it was just coincidence (it hadn't worked in over 3 weeks), and maybe all my squirrelling around with the ground and the fuses accomplished something after all?  If my window quits on me again (which has been the pattern up to now), I will take mr. jumper wire and stick it wherever it will do any good.
Mike