I had my defective #1 cylinder injector replaced by my mechanic. I noticed that #2&#3 injector's wiring, the plug on top, the red wire was facing the firewall, the white wire was facing the front. My mechanic had installed the plug for #1 cylinder red to the front and white to the firewall. Will this reversal cause damage/failure to the injector? Does the alignment matter? Thank you for any input.

 

No, the plug only goes in one way

 

Injectors are solenoids so have no polarity, as long as one wire is + and the other - it will work as designed

A solenoid is one wire wrapped around a metal "core", the wire is called the coil
When voltage/current is passed thru the coil, in either direction, the metal core becomes and electro-magnet
Depending it is purpose this electro-magnet can be used to pull open a valve or move an arm
In the case of an injector it pulls open a valve allowing fuel to be sprayed into an engine

On a starter motor the solenoid pulls on an arm and that pushes starter motor gear out to engage the ring gear on flywheel

 

The two wires that plug into the top of the injector are red, 12 volts constant, and white which is the 12 volts to trigger the injector opening and closing. My mechanic installed/forced the plug on backwards. Will this reversal damage the guts/parts of the injector? Put my test light to red wire, turn the key on, 12 volts. Connect the test light to the positive of the battery, start the truck, and check the white wire and the light flashes so output to the plug is good. Also checked 1,2,and 3 injectors with VOM and all read very close. Compression was 130lbs. This all started with check engine light and mechanic's meter said bad injector #1 which he replaced, plug on backwards. I have reversed the plug, disconnected the battery, reconnected and driven to reset the computer. Still get check engine light, misfire # 1 with my reader. Replaced all the wires replaced the plugs checked for spark with the plug pulled and grounded to the block. 197,000 miles, may be time for something newer. Thanks for the input.

 

Only 1 red wire per injector and yes it has 12volt with key on
The other wire at each injector runs back to engine computer, and it will show 12v if its plugged into injector because an injector is just a coil of wire, 12volt IN = 12volt OUT
But the computer will ground that wire when it wants to open that injector

Its impossible to plug in an injector backwards as it has no polarity, no + or - side, as long as both wires are making contact then it will work as designed
As far as the connector fitment, yes that can be reversed and won't hold well or won't allow a good connection for the 2 wires for that injector

Simple test to see if an injector is working is to unplug the coil pack, so no spark
Crank the cold engine over a few times
Pull out spark plugs
Tips should be WET with fuel
Dry tip is a bad injector

3.0l Vulcan engine runs 9.3:1 compression ratio, so expected compression is 160-170psi

But you have to test all 6 cylinders with all spark plugs removed with same compression gauge to get an average number, and then you decide if compression is a factor in one, or more, cylinders
Compression test on one cylinder won't help much unless it comes back as 0psi, lol, then that would be a bad cylinder
130psi is low for a static test, that means running compression is about 75psi which is getting low enough to cause a misfire

I would do a full test, all spark plugs out, press gas pedal to the floor while cranking, shuts off injectors and also gives full air flow
Get at least 5 "hits" per cylinder then write it down and test the next one
Add up the 3 cylinders with closes numbers, and divide by 3, that will give you the average
Any cylinder 10% lower than that is suspect
So if average was 155psi then any cylinder 15psi less would be suspect, so lower that 140psi

You can add a teaspoon of oil to a low cylinder and re-test, it will go up in psi for sure, but if it doesn't come up to the average or above then compression loss is a bad valve seal