Ok, it's clear that in reading the response by TnBob and by the way, thank you, I don't have a clue what this all means. Thought I might go to Sears or Lowes and pickup a meter and maybe then some of this will make more sense. Are those Cenn-Tech units from Harbor Freight? I'd like to do some more work on this tomorrow. Thanks again for the input. I was definitely feeling lost in space today but maybe a few tests can bring me back!

Meters aren't too difficult. You'll rarely try to read current in cars, mostly voltage and continuity. But you do have to respect electricity or you'll end up trying to weld your test lead to your car or your battery at some point. That's never happened to me...

If in doubt, post a pic of the controls of whatever meter you buy, and someone will chime in with settings and lead connections.

I went to the posted startek site. Fuse 12 in your car is busy.

I'd disconnect the cruise completely, possibly unplug the turn signal relay, and look under the hood for chafing or loose wires. There are a few more pages of gauge connections, but I think the pdf covers the likely culprits for your car.

Attached Files

83 300SD fuse 12.pdf (478.1 KB, 119 views)

Yes, the Cenntech ones are at harbor freight. Get it there.. I saw the same exact unit (just different "brand" sticker) at Advance Auto for $20!

Here is an idea:
Monitor the current at the fuse as I've indicated and unplug devices that are connect to is as indicated by Yak's PDF and see how the current does. If you see a significant drop, perhaps thats your culprit and if everything is unplugged well then something aftermarket is connected in or you've got a bum wire somewhere

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Yak, thanks for the info and the link. It will probably help out. I wanted to summarize where I stand so far with tests and observations:

I cannot get the fuse to blow applying the brake sitting in the driveway.
Just driving slow around the neighborhood the fuse won't blow.
Seems to only blow the fuse after being up to about 30 mph.
The fuse will blow with the combination switch disconnected.
Fuse will not blow with tailights disconnected.
A red fuse will blow also even though it's twice the size.

I disconnected the cruise control thing under the glove box but not the actuator. Where is the actuator located? I'm curious and suspecious about the warning system stuff because it doesn't seem like any of that stuff works at all. Also, where is the turn signal relay?

Thanks again all for the input and help!! Very much appreciated!!!!!!

Thanks for the summary! That's very helpful.

The actuator is connected directly to the amplifier under the dash, so effectively its disconnected.

Try this, look in the driver's footwell. Remove the carpeted piece thats on the center console. There is a connector down there that connects backup tail lights and speedometer signal and a few other things. See if anything is a miss there.

On the 560SEL, that connector was taken apart and we had no speedometer or rear backup lights.. that was the culprit.

The only thing I can think of that change when you go from standing to 30+mph is the speedometer input signal. This signal is generated by a sensor on the tail of the transmission. I believe its an inductive pickup sensor for your car, hall-effect for newer. Perhaps it is grounding out somewhere.

You're clearly taking down more than 16A when it goes. Something is grounding out when it shouldn't be.

Another idea might be the warning relay, I believe its right next to the cruise control box.. I've read things can fail inside those and you lose the buzzer..

Finally, double check your tail light harnesses, just make sure they look clean and you dont see any wires touching each other. You should be able to connect your new meter to ground and the 12V wire on the harness and verify there is no continuity.

Just some ideas.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

JamesDean, I see a meter on HF website just like the one you had a picture of for $3.00! That seems to good to be true but I'll go fetch one up in the morning. I'm from Idaho so maybe I could get you to go reeall slooow and explain how to set up the meter on the fuse. I guess the car would be running?

Certainly, its very simple.

Set the meter to 10A (about 5-o'clock)

Connect the probes appropriately (black to COM, red to 10A).

Put one lead (doesnt matter which) on the top copper spring clip where the fuse would sit, and the other where the bottom of the fuse would sit.

You are simply replacing the fuse with the meter. For the purpose of this experiment you don't want to let them sit too long, as the meter is unfused, just long enough to get a reading. A few seconds, the number should steady out to something.

I'll check my SD shortly and post a picture for reference.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

JamesDean, the warning relay is interesting because there's never any warning buzzer for anything. The sensor on the tranny is an interesting idea also. I'm looking forward to trying these ideas out!

Hm the warning relay is interesting. When mine was ON, I had a .750 A draw on the circuit, other wise the circuit only drew what the picture shows:

Hope this helps when you go to test yours.




Those large black relays you see aren't factory, I added them in for the keyless entry system, don't mind them.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

I assume the meter also has specific settings for current with the lead positions - if so, make sure the wires are plugged into the correct places.

Measuring volts, or ohms, you might need to move the wires.

A tiny bit of meter theory:

Measuring volts, the electricity doesn't flow through the meter - it's an open circuit.
Measuring amps, it does flow through, so it's a short circuit.
Measuring ohms, it needs a little power to measure the voltage drop, so it ADDS current.

As long as you know what you're trying to measure, you can just read the face of the meter to set it up. Sometimes it's useful to get a sanity check by measuring a known quantity; e.g. "am I using this right? Is it measuring correctly, or at least what I'm looking for?"

That $3 meter is the correct one. It will eventually need a new 9V battery if you do much resistance checking.

At $3 consider getting 2 meters ~!~

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

Ok, got the meter. I set it on 10a, removed #12 fuse and tested. Here are the numbers:

Key on engine off = .64
Engine running = .62
Engine running brakes on = 4.01 max
Engine running, brake on, left turn signal on = 6.50 max
Engine running, brake on, right turn signal on = 6.89 max

I went under the car and found the single wire going to the back of the tranny and at first I thought it was rubbed raw on the crossmember but I don't think it is. What happens if this is disconnected?

Do I need to remove the center console stuff to get that carpet off the side of it? I took the floor carpet out but was afraid to yank to hard on that side carpet.

I disconnected a plug that was to the left of the cruise control amplifier, is that the warning thingy?

Thanks to all for the guidance and help!

Thank you Yak for the Meter Theory info! That's helps and it will be really great for me to get a better understanding of this stuff!

These numbers all sound acceptable. Each tail light / turning light is about 1.5 A draw each.

That is probably the speedometer sensor wire.

The center console carpet is held in by a screw in the vicinity of the gas pedal. If you've removed the knee panel, remove the screw and the carpeting should be able to be removed.

It should have been to the right of the cruise control unit, they share a bracket.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

On the far right side under the glove box there is only one box on that bracket. Maybe I should get a photo.

Ok, removed the the carpet on the drivers side of the console. There is an odd looking coiled white wire in a deteriorated sheath that goes out the side of the tunnel near the tranny. I saw it while underneath also and it doesn't go to anything. Small gauge white wire, very strange looking.