motronic tachometer

[bullit 0]

Hello everyone,

My name is Ben. I'm french so sorry for my english. I installed a motronic on my 205 gti. The engine starts but the tachometer does not work. I took a good look at the photos to put a wire in the tachometer, but I can't really see where to solder this wire. Same question for the seer "K".

Thank you in advance

Ben

[petert 587]

It doesn't change. There is no need to modify the tacho. The tacho is still triggered by the negative side of the coil. Connect the green shielded wire to that.

There is no K light on a Jetronic dash. When I do a conversion I use the choke light. Thus connect pin 15 of the ECU to the choke light (wire 75). The ecu is grounding out the K light (L33), thus you might to supply +12V to the other side. I can't recall.

Edited October 7, 2020 by petert

[pug_ham 244 3 Cars]

What motronic ecu did you put on your car?

 

If it's the ML1.3 as fitted to the cat equipped 205 as original then like peter says, you shouldn't need to make any change but if you used a later motronic system with the rpm signal from the ecu then you will need to either modify your existing rev counter or get a converter.

 

There are guides for either of these methods on here somewhere if you run a search.

 

g

[Thijs_Rallye 87 4 Cars]

There is no soldering involved if you want to use the tacho. It needs a switched live, earth/ground and the signal wire in the 4 pin connector. Signal wire attaches to coil negative as Peter said.

[bullit 0]

Thank you for your feedback. I have a motronic 3.1 calculator and loom  from bx gti. I do have a 112 son. I don't see a green shielded wire? At first I wanted to do it like this but I was afraid of breaking my meter.

 

I saw that we can put an adapter with diodes but I don't understand how to do it and where to connect it. Do you have pictures of this montage ? Thanks 

 

Edited October 7, 2020 by bullit
erreur

[SRDT 177]

Pin 1 and 2 on the coil, those that goes to the ignition module.

You can also use the BX tacho with the 205 face or hunt a XU5M tacho from a 309.

 

There is more info on the MP3.1 here:

 

 

 

[petert 587]

You need to connect to pin 1 of the IC, labelled A in my pic. If you trace back around the board, you'll notice the pad area B, is electrically the same point. That bypasses all the filter inputs and goes direct to the IC.

[bullit 0]

I'm afraid to open my counter. I prefer to put an adaptor. Where do coil A and coil B wires come from? They must be taken from the ignition mode plug? If so, you have to cut or make a splice and put the diodes.

Thanks