^That is some great info, thanks for posting it.

So I'm guessing the single wire from the sensor grounds the circuit. Although I've found some strange wiring methods on these cars, so I've learned to never assume. But if that's the case you would just wire up a light and have the ground go to the sensor wire. Wish it was easy to test is all.

-Rog

My issue with a system which put a light in the ground circuit would be the bulb failing which would cause the circuit to fail.

If I wanted a light to tell me when the ALDA is limiting boost I'd run a hot off of one of the fuses and splice into the BR/BK going to the intake sensor.

Since the BR/BK goes through the main ele loom and into the lower cavity of the fuse box that is where I'd make the connection. It would also give access to the bottom of the fuse bus which would accommodate the attachment of the hot for that light to a fuse.

That entire fuse bus comes up by removing two screws from the front of the platform and lifting the platform while pulling it toward the front of the car. with a little tug the frontmost part of the bus will lift straight up allowing for work in the lower cavity of the fuse box.

The ground connection could also be done in a connector, C153 which is mounted vertical on the diagnostic plug housing, connector pin #3. Fishing the wire through the fuse box would be the tough part of that exercise. I wouldn't trust another path due to the possibility that a faulty ground would trigger the ALDA and limit boost.

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84 300SD
85 380SE
83 528e
95 318ic

At least the warning light also informs you of a ground fault Do you really need such a thing? Don't you know your car well enough to wonder, "Dang, she's particularly peppy today... " In a previous life I added warning lights to a turbo gasser for fuel cut (its version of overboost protection) and knock sensor frequency.

Sixto
83 300SD

If the overboost switch gets activated you'll know... it will pulse on and off and you'll feel it in the engine's power.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

If you have no ALDA and or switchover valve then a light would be helpful I think.

I think I was too casual in my explanation of my thoughts on the light... I'm not saying to put the light in line with the sensor wire, but for the light to have its own power on one side and then ground via the sensor wire in parallel with the switchover valve.

I know people have done this, as I've seen mention of it. Just not sure where they spliced in.

-Rog