What is this unit and could this be my problem? - PeachParts Mercedes-Benz Forum

mbzr4ever · #1 07-05-2009, 08:21 PM

I was posting on another thread about changing bulbs in the instrument cluster, but now my engine won't start.

When I turn the ignition, I get no light on the glow plug bulb. The headlights dim considerably, when I start to turn the key all the way and there is no cranking noise, an odd clicking/buzzing noise from the silver box (left of steering wheel) pictured below. I think this is the glow plug relay?

So I take the multimeter to the battery, seems ok (got almost 13V).

Then, to this other unit (under the hood and under the driver side windshield wiper), and the other wires get around the same ohm reading (approx 2), but the one I am pointing to does not change. Could this be the source of my problem?

FYI, I changed all the glow plugs about a year ago. This whole problem started again when messing with the instrument cluster with should have been just a simple bulb switch. Oh well, I think it was time to tackle this problem: ignition switch, starter, relay, tumbler, any or all connections.....

FineOlBenz · #2 07-05-2009, 08:26 PM

Sounds like you have a dead battery. the glow plug relay is located on the left front fender forward of the shock tower.

mbzr4ever · #3 07-05-2009, 09:33 PM

Ummm, the battery registered a bit under 13 volts with the multimeter, and the headlights came on.

I may be a girl, but I don't think a dead battery would do this.

Maybe a weak battery, but not a dead one.

Diesel911 · #4 07-05-2009, 10:22 PM

Here are some pics of relays I found when I looked up the parts for your 79.
The Seat Belt Relay looks similar to the 1st Glow Plug relay pic but it has 10 pins on it. (Added 3rd pic of Seat belt Relay)
1st is a Glow Plug Relay and it has 7 pins.
2nd is another Glow Plug Relay listed for CA cars.

tbomachines · #5 07-05-2009, 10:31 PM

You could have jostled one of the wires to the ignition switch, just visually check that. Check the voltage at the starter motor, see if it is getting any. I'm guessing it isn't - then just trace it back. Sounds like you're handy with a multimeter, so I would start at the starter motor and work your way back electrically to see what is getting power. I can't think of anything that would affect the starter by pulling the cluster except for a broken ignitino switch wire.

winmutt · #6 07-05-2009, 11:00 PM

I vote for battery as well, or ground.

bigblockchev · #7 07-05-2009, 11:25 PM

In order to get an idea where your problem lies try this. hook up the multimeter to the battery and try to start the engine. As the clicking noise is going on what happens to the voltage on the meter. If the voltage doesn't go down much then there is a problem in the starter circuit ie ign switch , starter solenoid or neutral interlock. If the voltage dips to a couple of volts then I would look at the battery or the battery terminals or even the starter cables , tighten all connection nuts on the terminals & don't forget the ground straps to the engine. Cheers Dan

Skippy · #8 07-05-2009, 11:27 PM

I'm going with the battery theory. 13 volts open circuit doesn't tell you the voltage under load, which is what you really need.

Sbean · #9 07-06-2009, 12:22 AM

All electrical connections must be not only tight, but confirmed clean first.
Steve

mbzr4ever · #10 07-06-2009, 12:54 AM

thanks, guys!

(grabs multimeter and runs to get more readings...)

diesel911, I'm pretty sure it is the 1st pix.

bigblockchev,

Any tricks to doing this by myself??? My closest neighbor doesn't come back from vacation for another month.

OK, with all the comments about the battery, I will pull the battery tomorrow and take it to the battery shop and have them test/recharge it.

I just don't understand how messing with the instrument cluster can cause the battery to fail. I can see a wire or something in the ignition switch area, but the battery???

cdplayer · #11 07-06-2009, 01:39 AM

Referring to diesel911 pics, first pic is your pretimed glowplug relay and it is located under the dash very near the steering column. One 8mm bolt holds it in place.

Second pic is a glo plug relay located engine compartment drivers side fender hump. Third pic is your seat belt buzzer relay located to the left of your pretimed glow plug relay under dash below A pillar.

If you have electrical trouble each time you remove instrument cluster, make sure the large pigtail at the lower left(facing cluster) is plugged in properly. Should be only one way to plug it in. But if you forced it at some point, you may have altered the pins.

mbzr4ever · #12 07-06-2009, 02:04 AM

cdplayer,

Yes, it is the first pic - I just went out to confirm the number of pins (7).

The buzzing/clicking noise is coming from this GP relay box.

(Now, I'm hoping this is just a simple battery problem.)

Not sure I have the item in the middle, the black relay box. This is a 240D that was factory built in Germany, not for CA specs.

bigblockchev · #13 07-06-2009, 02:20 AM

If you wedge the multimeter leads into the battery terminals and position the meter facing the windshield you should be able to see the meter while you are trying to crank the engine. Troubleshooting anything is a matter of looking at the empirical evidence. Sometimes you can be fooled by unconnected factors. If you methodically go through each component verifying one step at a time you will get the answer. If you can feed us the results of your testing there are lots of members who will be happy to guide you. Cheers Dan

mbzr4ever · #14 07-06-2009, 02:25 AM

bigblockchev,

Great idea about resting the meter on windshield.

That is what I really appreciate about this car. It's simple design allows the steps to be broken down easily, even for a newbie like me.

Thanks for your support.

Diesel911 · #15 07-06-2009, 01:00 PM

Quote:

Originally Posted by mbzr4ever

cdplayer,

Yes, it is the first pic - I just went out to confirm the number of pins (7).

The buzzing/clicking noise is coming from this GP relay box.

(Now, I'm hoping this is just a simple battery problem.)

Not sure I have the item in the middle, the black relay box. This is a 240D that was factory built in Germany, not for CA specs.

The Black Relay is a Glow Plug Relay that was only used on California Cars. I included it as I did not know where your Car came From.

I would test the Car with and Without the Glow Plug Relay. It may not be related to your problem but one of the wires that goes to the Glow Plug Relay goes to a Temperature Sensor somewhere on the Engine.

Unfortunately I have not seen a good writeup on how to trouble shoot the type of Glow Plug Relay that you have.
There is a Strip Fuse somewhere for the Glow Plug Relay. On the older 300Ds it is under a plastic cover somewhere on the Fire Wall on the Drivers side.