Ideally, a cct test needs to draw a similar current to the rated load on that circuit - a test light is great for basic cct integrity - but might not draw enough current to find the real issue - The LED test lights are notorious for this, needing microamps to illuminate
You'd need to know the size of the lamp, and thus the current draw it demands..
My preference is to use lamps of various sizes - for example, a headlamp - given each filament will draw about 4.6A - and a 21W bulb will draw about 1.7A ....so, if your solenoid circuit will run a 21W bulb without issue, then it is fine.... ( it's a great use for headlamps with one blown filament ...
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Change the FIP and the injectors - BUT, you loose a lot of power in so doing, so you "need" to fit a full width intercooler and then tune the thing properly ( or better, get someone who has the proper kit, and get them to do it ) - it's a last resort really - but, to me, who hates electronics and modern vehicle "reliability" - it was the only way forward..... I now have 146HP and no electronics ....
Well, take as much care of it as you can
- be careful near the wires etc .... mine let the smoke out, so I had no option
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Ah - technically yes.... When mine died, about 5 years ago, I was quoted over £1K to build a new injector !! ....