Hi,
I've been tinkering w/ my electrical system and decided to replace all my fuses (I wanted to clean the contacts, and thought I might as well replace them). They appear to be the newer type, and look fine.
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?

Another question: The reason I've been working on my electrical system is I've got some intermittant problems w/ some of my secondary compontents. Sometimes the light on the transmission shift **** works; sometimes it doesn't. Same w/ my radio, the antenna, and the right rear window. These things will work for awhile, then quit for a while, then start working again. I decided to improve my ground, and replaced my ground strap, added another, added a second battery ground (one to the alternator, one to the sheet metal), and added a ground between the engine and the firewall. I've also (from above) decided to replace the fuses, w/ the exception of the two described above. Has anyone beaten this particular electrical boogeyman before? What did you do?

 

acting as resistor?
it's still a 25 amp break, and still the same as what they use now.

fair enough.

 

Sleepwalker,
Would I be correctly inferring that you would be inclined to replace the #3 fuse w/ another 25A - even though the spec calls for a 16A - and then replace the #1 w/ an 8A as the spec calls for? If so, that was sort of what I was thinking.
I'll have to keep scratching my head why someone would increase the fuse size from 16A to 25A to allow more amperage, then add another 25A fuse as a resistor. But that may make perfect sense to an auto electric guy who knows what he's doing. As for me, if you were to watch me work on auto electric issues for awhile, you would likely swear you were looking at the missing link!

 

ONe reason to increase the size of the fuse is the previous owner might ahve hooked up and additional accessory to the fuse. ie. On my 79 450SLC, the fog light only turn on when the headlights are on. I found the wire from the light switch for the first pull out detent and rewired it to the parking lights. So I added a fuse with 8 more amps to compensate for the extra load on the parking lights. Are they anything "extras" that didn't come wikth the car when new? Such as aux lights etc?

 

right.

 

for #1 fuse, it doesn't really go far from the original amperage. nowadays, fuses were in 5, 7.5, 10, 15, 20, 25, etc amp.

you're right to say "someone wiser than I in the ancient mystical art of auto electronics" because they calculate to a very little tolerance.

25A for A/C is okay. it takes 30A for the blower to start smoking

 

I learned a $2200 lesson about auto wiring. When i was 16 i looked outside at my 300sdl and thought "looks like smoke in my car" so i went outside and i was so i quickly pushed the car off the carport away from the house and other cars. I had put a new bullb in one of the puddle lights and one of the plasic covers came off the plug and i did not cover it. They had touched and melted my entire interior electrical harness. Last time i forget to use black tap on a connection

 

Hey guys,
All of you contributed to my coming to a singular important conclusion: if you don't know what the heck you're doing, please don't do it to your electrical system! I had been intending to replace the 16A w/ an 8 on #1 and leave the 25A same same, but now I think I'll just keep their amperages as they are. There are only two possibilities here: someone made a mistake, or someone changed it for a reason. Since I don't know enough about electronics to know which applies, and since nothing really BAD seems to have happened as a result of the changes, I think I'll leave well enough alone.
I don't know nearly enough about auto electric, but have decided if I'm going to keep an old car around, I'd better learn. I've been reading a few books on the subject and it's really amazing to read about the genius that is demonstrated in the automobile. It's really quite fascinating stuff. Now if only all the wires were out in the open so I could see them... Thanks for benefitting me with your wisdom and experience.
Mike