Volvo 164 injector voltage issue

I've been trying to get my 72 Volvo 164 back on the road after 20 years, and after some testing, have found that the 2 injector batches have different voltages. With a 3v LED at the end of the plug, one batch fires nice and bright, and the second batch is quite dim, closer to the 2v range. Any one have a clue what is going on? 

Hi Unknown,
Welcome to the forum. It would be nice you could sign with your first name so that we can address you directly.

Concerning your problem, you should find out it's a problem of the ECU or the injection harness.
I don't think any other component can be the reason for this.

I know your ECU is placed in a location that doesn't invite working there... but you have to do some readings from there to check the continuity of the wiring.
Pull the plug out of the ECU and check the resistance of the injectors connected to the wiring <disconnect your LEDs>.
You will find the numbers of the pins printed on the wires and the ECU-plug.

You will find a general description and a specific plan for your car here: jetronic.org/de/forum/jetronic/19-messpl...ents-by-car-model#68

Regards
Norbert