I added a feature to the Glow Plug Relay so the dash indicator now serves another purpose: it shows when the glow plugs are active (relay is closed). Many people think the dash indicator is telling them this already - but that's not the case. It's only a suggested serving of glow, and can go off even when the GP's are powered.

Adding one resistor was all it took. The resistor puts the dash indicator at "half brightness" for showing when the GP's are powered (relay closed).

The dash indicator still shows the original MBenz intentions (suggested glow time is over, and GP fault/s) using its normal full brightness. Any normal full bright activity overrides the mod, so you'll see full bright.

So now, a normal start cycle shows a full bright indicator up to the "recommended dose" and then goes to half brightness and remains that way for up to 30s, or up to and throughout the cranking period, and then the lamp goes off as that's when the GPR releases.

If for some reason the relay sticks (at any time with key in the car or not) the indicator remains lit at half brightness.

Why didn't MBenz think of this?!? Sure beats running a second wire and adding another bulb to the dash.

Here's a picture of the GPR mod showing the resistor added to the solder side of the GPR circuit board. It's so simple it almost doesn't need any explanation. If you don't read resistor color stripes, it's a 47 Ohm resistor, 1/2 Watt is fine. One end of the resistor pokes through a hole MBenz left for an unpopulated part (remember to trim it flush on the other side of the board!), and other end of the resistor gets tacked onto the lamp lug.

This is for a stock 1987 300D GPR. The same idea can probably be applied to other model year GPR, by adding a similar bridging resistor between the relay output and the lamp output.

Attached Thumbnails

 

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Cheers!
Scott McPhee

1987 300D