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Old 10-28-2009, 09:31 PM
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Join Date: Oct 2009
Location: Georgia
Posts: 6
electrical Problem 1977 450Sl

My 77 450 SL overheated and I have effected all repairs only to find out that the car developed a electrical problem. I have several issues found IE. the tach, fuel gages, turn signals, 4 way flashers, power windows and antenna do not work. I have check all the fuses both visually and replace a few but can not find the problem. Can anyone help provide me a place to start baffled and piss off
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Old 10-29-2009, 03:11 AM
coleyjf's Avatar
Old dog - new tricks
Join Date: May 2005
Location: East Midlands of the UK
Posts: 264
Hi there:

It doesn't sound like a fuse problem as you are describing systems using at least 4 different fuses on both the upper and lower row so you can at least rule a blown or badly seated fuse out. ( eg Windows are on fuses 3 & 4 and the relay for them is on fuse 5 plus the antenna is on fuse 12)

Sounds like a major wiring (loom/harness) fault, Did you "pull" or disturb an multi-way connectors such as those between the engine bay and the bulkhead when fixing the overheating fault - or could the wiring loom have been damaged either when it overheated or in the repair?

Happy fault hunting.


Keep your Motor runnin'

Jim's '88 300SL
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Old 10-29-2009, 06:50 AM
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Join Date: Jun 2009
Posts: 111
I can understand your frustration. Trust me on that one. Start with one circuit and at the fuse panel. Use a tester. The kind with a light in it. If there is a short you will notice it when you touch the top and bottom of the fuse contacts because the light will light up.
Ask yourself this one question. when did these problems occur? Did they happen when you have the vehicle. If so what did you do. Did you rewire the 4 way hazard flshers?
I will tell you that the wiring loom is capable of taking a beating and will keep on ticking. In this case try not to make a mountain out of a mole hill.
Track the antenna first. disconnect the switch and check for power with a multimeter. If you have power then determine the wires going to the antenna. Check for grounding or corrosion going that way.
Power is affected through the 4 way flashers going to the instrument panel. Google "hazard switch configuration 450sl" Or something close. I had to. Someone figured out the wiring configuration to the hazards and BINGO problem was solved.
The fuse panel is color coded for amp rated fuses. Hard to look and verify fuses blown. Take a digital camera and get a couple of good shots so you can see clearly each and every fuse. You might be surprized to find out if there are fuses that might not belong in the correct slots.
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Old 10-29-2009, 10:07 AM
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look at your common grounds, one or more may have been melted?? How hot are we talking??
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Old 10-30-2009, 06:10 PM
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Join Date: Oct 2009
Location: Georgia
Posts: 6
Post Electrical Problem

I would like to thank all for the information provide. The problem was really discovered while the car was overheating. I first saw the gages went dead while the car overheated. That is was I am trying to tie the overheating to a cause and effect problem. I have a Hayes book that describes a thermal switch/relay what is the function of thermal switch. My aux electric fan has never started also after repairs. I have purchase the fan switch but I can find the location of the sensor Help. And I will start looking for the ground this weekend. Keep the info coming I really appreciate

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Old 11-08-2009, 07:39 AM
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Join Date: Oct 2009
Location: Georgia
Posts: 6
Smile Found the Problem Electrical

1977 450 SL
After not trusting my eyes and removing and checking my fuses with a fluke. I discovered that I had replaced a fuse with a under rated fuse and it blew again. I replace it with the correct fuses and I am back on the road runing. I would like to thank you all the help and motivation to keep going. I am looking for the help on parts
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Old 11-08-2009, 07:48 AM
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Join Date: Oct 2009
Location: Georgia
Posts: 6
Looking for parts for MY 77 450 SL

During my last repairs a noticed that I need to replace a few body parts. I need both inner and outer fender for both sides. Along with lower front Valence. I also need the sun visor clips both for Bambu interior Any direction to a parts place that has reasonable price would help
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