P38A Bu99er and question

Hi all, so following on from my previous trials and tribulations I was lucky enough to receive, as part of the gasket set I ordered, a new set of 'O' rings which I deduced to be for replacing the old ones on injectors.
2 weeks ago, Nanocom reported Injector 6 was up the spout. Long story short I finally got round to swapping it today.
Turning on the ignition saw petrol (about £3759.53's worth at today's prices) pouring from the fuel rail at injector 4. A post all-put-back-together-again check shows that the replacement new 'O' rings are smaller than the old ones. Bu99er.
So now I've to source some new ones and live, die, repeat the exercise.
The question is: is it possible to test/check for a signal to the injector (in case its an electrical problem) using a standard multimeter or similar?

I'd think the pulses are so quick and fast an oscilloscope would be better.

Thought as much, and not something most people have as a rule. Thanks though

Thought I'd try the local dealer for a new set of 'O' rings: "Yes we can get those for tomorrow morning". "How much?" asked I. "About £70......."
Click...purrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

Feck that......

Independent: "yeah , we can get those, they're about 30p each....."

Sorted new 'O' rings installed, still running dog rough. A quick search tonight found a short at the rear of No6. Soldering by a trained amoeba by the look of it. Duly mended. Vroom and purr. Big smile.