'80 300SD: Need encouragement (and advice)... about to remove instrument cluster

[Tony66_au]

A few things I have to point out, the simple act of replacing an 8 amp fuse with a 16 amp fuse will not damage a thing.

Well, I would never do it.

Good info about the corrosion and age causing more current draw because of a higher resistance, though.

Well the difference in time between an 8, 10 or 16 amp fuse blowing in a car is literally milliseconds and auto fuses on old cars are purely to prevent fires so swapping a white for a red is fine and with these cars being as old as they are probably not a bad idea as the majority of 8 amp fuses will be running close to their limits with the aged looms.

A check with a pyrometer will tell the story

[JasonP]

I completely disagree. How can you possibly say it is a good idea to double the current in a rated circuit?

How can you give advice to someone to do this? If Mercedes rated a circuit for 8 Amps, why would it be O.K. to put in a 16 Amp fuse?

Like I said, knock yourself out. I would never do it, and I would never have it done on my car.

[Tony66_au]

I completely disagree. How can you possibly say it is a good idea to double the current in a rated circuit?

How can you give advice to someone to do this? If Mercedes rated a circuit for 8 Amps, why would it be O.K. to put in a 16 Amp fuse?

Like I said, knock yourself out. I would never do it, and I would never have it done on my car.

Ewwwww kay....

Over react much?

First up, I am educated in both Digital and Analogue electronics and have Auto and Heavy vehicle electrical experience as well as in retrofitting cars and i have also scratch built hundreds of looms to OE spec and higher with experience in 60's and 70's classic cars.

Secondly, Dont put words in my mouth because your statement "How can you possibly say it is a good idea to double the current in a rated circuit?" is both false and misleading as I did not say that.

As for the "Rated circuit"?  Well if you had understood what I have taken the time to write out then you would see that your "Rated Circuit" was now a higher amperage than the factory spec 30 to 40 years ago due to corrosion and bad connections.

Finally a Pyrometer is a point and shoot device that measures temperature at a specific laser designated point.

So where the red dot sits is what the displayed temperature is.

I use one for many things from telling how hot my BBQ hotplate is to finding hot spots on performance engines and it is a very helpful tool in spotting electrical circuits that are generating heat, a simple diagnostic that when pointed at a fuse tells me if and how much hotter than the surrounding fuses a single fuse it.

I can then bridge out the fuse with an ammeter to see what the current draw is so I can remedy the situation by creating a better earth and checking the connections right down to sometimes paring the end off a connector and reterminating it with non corroded wire.

Metal element fuses are far from exact as I hinted at before and their main function is to break the circuit if there is a dead short or high current spike to prevent the loom catching fire.

If you replaced your Fuses with electronic breakers (A simple enough job on a weekend) available from any Caravan or RV accessories store or even eBay Id put money on your 8 amp breaker tripping every time you turned the circuit on, infact id wager that even with a 10 amp breaker your 8 amp circuit would keep tripping because of its age.

Trippy huh?

Now go read my posts again slowly, digest them, apply logic and perspective and then if you still disagree im really not interested.

Tony

[WrightSounds]

WrightSounds,

To remove the instrument cluster:

1) Cover the top of the steering column with a soft towel to avoid any scratches
2) Carefully pull the cluster towards you from one side and then the other, you can use two fingers to "grab" the inside of the instrument binacles, be gentle and careful not to damage the wood.
3) Once the cluster is loose, you need to disconnect the oil pressure line from the back, it is a 10mm nut and you can reach it by tilting the inner portion of  the cluster , you will see the nut once you do that
4) Reach from behind and disconnect the speedo cable
5) Once the oil line is removed you should take out the main round plug from behind the combination gauge
6) There will be a cruise control connector to the speedo as well as a clock wire (RH side)  and another wire (blue I think)  connected by itself near the oil line

Installation is reverse, to make re-connecting the speedo cable easier, loosen the cable tie that holds the cable to the floor, you should be able to see it if you remove the driver's carpet.

Hope info helps.

Good luck.

Tks

Joe

Thanks for the detailed instructions Joe! I've printed them and put them in my MB folder. Lucky for me, I gave the dimmer switch another wiggle-and-rotate and the lights popped back on. Now NOBODY TOUCH THAT KNOB! 

[JasonP]

As for the "Rated circuit"?  Well if you had understood what I have taken the time to write out then you would see that your "Rated Circuit" was now a higher amperage than the factory spec 30 to 40 years ago due to corrosion and bad connections.

Then get rid of the corrosion and replace the bad connections.

Listen, we disagree. I don't have to agree with you. I was trying to be nice, I just said I wouldn't do it. (And I still won't.) I even complimented you on your information. And you're still carrying on.

All I did was give someone SOUND advice about their car, and then you're all up in my face. Nothing I said was incorrect or wrong. I advised the owner of a car to use the fuse that it calls for. Oooh! My bad!

You are the one insulting me, not the other way around.

Now go read my posts again slowly, digest them, apply logic and perspective and then if you still disagree im really not interested.

That's really not necessary. I'm not here to fight with you or exchange insults.

[scraf]

I advised the owner of a car to use the fuse that it calls for.

Did that a while back, changed like 90% of the incorrect fuses in the box back to spec. Then started having to upgrade the buggers to heavier ones, the electric window ones burnt out straight away, if I recall correctly.

[scraf]

I know! I'll quit my job as a guitar tech and become a Mercedes tech (strictly for 1980 300SD models... that are just like mine... and that have only had the same problems as mine  )

Working on a 300SD is like working on a Telecaster, a petrol jobbie, could be compared to something with active electronics and a Floyd Rose.

[jmperkins]

I see you've received a lot of good advise including how to remove the instrument cluster.

You've probably figured out that the cluster is held into the dash by a rubber gasket so it is just a matter of wiggling and pulling it out and like any other projects, not getting in a hurry and making sure all the wires and lines are disconnected before trying to remove it all the way!

[WrightSounds]

Working on a 300SD is like working on a Telecaster, a petrol jobbie, could be compared to something with active electronics and a Floyd Rose.

Ha! Awesome... finally a guitar reference! The attention to detail and patience I've learned from guitar repair has definitely helped with all this Mercedes Benz schtuff 

[Tony66_au]

As your Dash cluster will have been out before you will probably find that the loom has been freed from its bondage previously for dash globe replacements etc so you should on the initial removal have a bit more room to work removing oil pressure lines and loom plugs.

As I mentioned before WD40 Electrical contact cleaner works quite well (Although not as good as the old non Eco friendly stuff did) and it comes with a neat fold out Nozzle for blasting out grubby rheostats etc.

A job for another day im guessing!

[Tony66_au]

I advised the owner of a car to use the fuse that it calls for.

Did that a while back, changed like 90% of the incorrect fuses in the box back to spec. Then started having to upgrade the buggers to heavier ones, the electric window ones burnt out straight away, if I recall correctly.

Electric windows are usually a hassle if neglected, Added strain on carbon brush motors will make them suck amps like mad.

That said I cant think of any car I have played with of 30 odd years of age where the windows were as simple to repair and maintain as Mercedes.

[andyatcrux]

Matt, if you do end up removing the instrument cluster here is a link to a dieselgiant tutorial for repairing an odometer that I used when I had to repair mine: http://dieselgiant.com/repairyourodometer.htm  It will give you some visual info to go along with the instructions you got from Joe on how to remove the cluster. Regarding the conversation on fuses, I did have several of mine repeatedly blow when I first got the car. I noticed that corrosion on the teeth (or whatever they are called) in the fuse box. I removed all fuses, cleaned the corrosion off gently with some steel would and dialectic grease, wiped clean and haven't had the problem since. I did have the help of the original diagram to ensure the correct amperage for each slot. Lucky guess.

[rosenfe]

one other thing will help with removing cluster.loosen tension on speedo cabel from below,by the gas pedal.speedo cable is usually the most restrictive thing in pulling cluster far out enough to losen everythinh

[Casey]

The rheostats get corroded over time, it may not be "bad".  Just try turning it back and forth all the way a lot of times with the lights on, and you might end up pleasantly surprised.  On my first 300SD it was very difficult to find any position that there was light at all, but after this it worked pretty much perfect.  As you turn the knob you'll probably feel corrosion and as you do it more and more, the corrosion will wear down and the turning will get smoother.

You can remove it and clean it up or replace it, but this is a really easy try.