83 300sd Brake Lights Blown Fuse help please - Page 2 - PeachParts Mercedes-Benz Forum

oldsinner111 · #16 03-14-2012, 01:33 PM

If you notice the bulbs the Osram have lower wattage,where as the others higher wattage.Thats why I went to LEDs lowest wattage easier on alternator and battery.I was blowing fuses with the other bulbs

JamesDean · #17 03-14-2012, 01:57 PM

Quote:

Originally Posted by oldsinner111

If you notice the bulbs the Osram have lower wattage,where as the others higher wattage.Thats why I went to LEDs lowest wattage easier on alternator and battery.I was blowing fuses with the other bulbs

Sylvania/Osram's replacement guide (Lamp Replacement Guide View All Bulbs) says to use 7506 bulbs which are 21 watts, thats what I've always used. This is the wattage the factory used as indicated by the housing. Wattages are stamped on them IIRC.

ShadeTree300SD · #18 03-14-2012, 01:58 PM

Well, what to do, what to do! What is the FSM? The fuse box cover in this car says nothing about Anti Lock Brake System or Anti Theft Alarm System. There is some what appears to be some aftermarket alarm system stuff under there. I wonder if this might be an issue? I wonder if a guy could disconnect all that stuff? Am I at the spot where I have to take it to someone? I'd rather not of course!!

JamesDean · #19 03-14-2012, 02:18 PM

Quote:

Originally Posted by ShadeTree300SD

Well, what to do, what to do! What is the FSM? The fuse box cover in this car says nothing about Anti Lock Brake System or Anti Theft Alarm System. There is some what appears to be some aftermarket alarm system stuff under there. I wonder if this might be an issue? I wonder if a guy could disconnect all that stuff? Am I at the spot where I have to take it to someone? I'd rather not of course!!

The FSM = factory service manual.

Its free from Mercedes now:
Untitled Document

They didnt put ABS on until 1985 so you wouldnt have that, I dont think you'd have the alarm either. But if someone added something, I would suspect that immediately. You should disconnect the power line going the after market stuff, perhaps that is the problem.

Disconnecting the brake lights only alleviated 3.5 amps from the circuit. When you hit the brakes adding 3.5 amps put it over the 8amp fuse's limit.

So something else is on that circuit drawing more than the factory intended.

ShadeTree300SD · #20 03-14-2012, 03:22 PM

Good News!! I went under the dash armed with a pair of wire cutters and carefully removed all the aftermarket alarm stuff. I wasn't completely sure but you can tell the original work looks alot different than this cobbed up stuff! So I got rid of it, hooked up the taillights, combination switch and took it around the neighborhood. Could not get the fuse to blow so I thought if anything will make it blow (Murphy's Law) going out it traffic will! Voila! NO blown fuse!! Woo Hoo!!! True test will be tomorrow morning but I'm optimistic. So JamesDean, thank you very much for your help!! Also, thanks for the FSM link. This will come in handy. Thank you oldsinner111 for your useful input also!

JamesDean · #21 03-14-2012, 06:27 PM

Quote:

Originally Posted by ShadeTree300SD

Good News!! I went under the dash armed with a pair of wire cutters and carefully removed all the aftermarket alarm stuff. I wasn't completely sure but you can tell the original work looks alot different than this cobbed up stuff! So I got rid of it, hooked up the taillights, combination switch and took it around the neighborhood. Could not get the fuse to blow so I thought if anything will make it blow (Murphy's Law) going out it traffic will! Voila! NO blown fuse!! Woo Hoo!!! True test will be tomorrow morning but I'm optimistic. So JamesDean, thank you very much for your help!! Also, thanks for the FSM link. This will come in handy. Thank you oldsinner111 for your useful input also!

Always glad to help. Glad it worked out for you. Let us know how tomorrow morning goes as well!

ShadeTree300SD · #22 03-15-2012, 09:49 AM

So, yesterday after thinking we had solved the problem I drove around a lot. I drove to pick up my daughter from school and everything is fine. When I get home I put the under dash back together, I put the trunk back together and I revel in the accomplishment! Few hours later I take the car out completely confident and within a few brakings the fuse blew! I felt like crying! What a surprise and I can't believe it! I put in another fuse and it continued to work just fine for probably 15 miles of stop and go.

ShadeTree300SD · #23 03-15-2012, 10:37 AM

Just went out and within 3 brakings the fuse blew again. Not sure where to go from here. Any suggestions?

JamesDean · #24 03-15-2012, 11:46 AM

Have you done anything with cruise control lately? If you dont use it or it doesnt work, disconnect the amplifier unit. Its located under the driver's side dashboard. Left of the brake pedal. It has a 14-pin connector on it. Its on a bracket with a smaller module. Maybe your unit has failed catastrophically somehow. I've not encountered this before but its as likely as a candidate as any.

Are you sure you completely disconnected the aftermarket alarm unit from the car's power ?

ShadeTree300SD · #25 03-15-2012, 12:17 PM

Hi JamesDean, Thanks for hanging in there with me! I just crawled under the dash again and pulled out the remaining aftermarket alarm stuff. I actually went inside the fuse panel and removed where they were connected in there. I thought the same thing that maybe I hadn't got everything. The cruise control hasn't worked for years and years so I'll disconnect it as you suggest. I was wondering if any of those dash instruments on the same circuit could cause problems. The oil pressure gauge has been intermitent for a couple of years but has never been a problem. Thanks again!

JamesDean · #26 03-15-2012, 12:22 PM

My 300SD's cruise units have been out for years as well. I've recently gotten into repairing the units actually, if you're interested send me a PM on here.

I'm not sure about the gauges actually.

What we might want to do is get a multimeter and set it to measure current and stick it where the fuse would go and see just how much current is flowing through that fuse.

I can do the same on my 300SD and we can compare numbers.

ShadeTree300SD · #27 03-15-2012, 02:07 PM

Ok, I really need to get a good multimeter. The one I have is not even useable. Are there any suggestions on a good all around meter for automotive work? Does the oil pressure gauge use any electricity? When I turn the key on and not starting the engine the oil pressure gauge pegs to the top and stays there until the fuse blows and then about a minute later it drops back down.

JamesDean · #28 03-15-2012, 02:44 PM

I have a Tripplet 9045 meter. But I bought that mainly for my electronics work. Its a really nice meter. Does all sorts of stuff, most stuff more expensive Fluke units do too. The Tripplet was around $80 I think.

For automotive work, the most basic of meter will work. I've got two of these $2 unit, http://www.smcelectronics.com/PICTURES/DVM1-L.JPG They cover 99% of what you need for the DIYer.

As for the oil gauge. I'm fairly certain stuck at 3 means something but I cant remember what exactly.

TnBob · #29 03-15-2012, 07:13 PM

x2 on the meter JamesDean suggested. They are plentiful on ebay for around $10 and being digital take a fair share of abuse (read that as being used by DIY'ers who know very little of meter use)

There are just a few meter things to know.

Do not every attempt to measure resistance with any power on the circuit. Doing so will usually result in the immediate destruction of that R reading position. Such as the 200 which is the most common scale we use.

Nice to check the meter by shorting the leads which should result in a 0 reading. If it doesnt note what it is .02, .03 so that when you check glow plugs you can subtract the shorted reading.

Voltage is taken with the Black lead, Com, sitting on ground and the Red to the area voltage is being checked like a fuse. Measure the DC volts at one end of the fuse ... 12 volts ... move to the other and read 0 volts you have a bad fuse.

Note that Resistance and Voltage readings are taken with the Black pushed into the common and the Red into the middle location.

Current readings are taken with the Red moved to the top position. A good rule of thumb if you arent used to reading current always start with the largest range ... in this meter 200M.

Measuring current is a tad more difficult in that the meter has to be inserted into the circuit usually by cutting a wire or a trace.

JamesDean · #30 03-15-2012, 07:45 PM

Sound advice, just some additions:

Quote:

Originally Posted by TnBob

Current readings are taken with the Red moved to the top position. A good rule of thumb if you arent used to reading current always start with the largest range ... in this meter 200M.

Measuring current is a tad more difficult in that the meter has to be inserted into the circuit usually by cutting a wire or a trace.

The Cenn-Tech unit has a 10A position just below the 200M position. Also the unit is fused to 200mA most circuits would pop that fuse easily.

I'm not aware of the 10A port being fused.

Additionally, the easiest way of measuring current on these cars is to get some alligator clips and clip the lead into the socket or onto the pin and just use a jumper wire to complete the other pin/socket connection.

Hopefully we can track down your problem!