PeachParts Mercedes-Benz Forum - View Single Post

pdxwaker · #9 11-02-2005, 10:48 AM

I'm still having problems with the glow indicator. Here's what I've measured at the glow plugs:

4 in: 7.83V
4 out: 6.58V
w-wire (resistor)
3 in: 4.9V
3 out: 3.74V
u-wire (not meant to be resistive)
2 in: 3.66V
2 out: 2.72V
w-wire (resistor)
1 in: 1.12V
1 out: GND (measured 72mV relative to battery GND)

So... 1.25V at GP4, 1.16V at GP3, 0.94V at GP2, and 1.05V at GP1. Note that these measurements aren't perfect... I had to use the w-wire to connect to the plugs so there is some additional resistance (I tried to measure as close to the plug as possible). The input voltage at 4 seems low to me but I'm not familiar enough with the circuit to say so for sure. Note that my alternator light dims significantly while cycling the plugs indicating somewhat strong current.

I also checked voltage at GP4 (in) when starting... 7.42V... a slight drop due to additional (significant) starter current.

I'm still getting no glow at the indicator regardless of how long I cycle the plugs for. All my shop manual shows for the circuit is a dual position switch on the starter knob which turns on the circuit. There is a 'resistive control unit' in series with the glow plugs and w-wires. No indicator is shown in the circuit... would this be the same as the 'resistive control unit'?

Anyway, before I dig into my dashboard (not easily accessible) I thought I'd seek advice. Is there anyone out there with 220d experience who can better explain the circuit? I'd really be surprised if 50A of glow plug current is supposed to flow through the starter switch. Is there no relay involved? What exactly is the 'resistive control unit' and where is it located?

The good news is that I'm still starting at ~45F... a bit rough but starting. I haven't been able to measure glow plug current yet... I don't have the necessary meter.