Hey everyone just wanted to throw this out there because I just went through it.  I have a 62 F100 4X4 with fuel injection and a lot of other electronics wired into it.  I have MSD 6AL box, fuel injection computer, trans control computer, electric fans and electric gauges.  When I installed all this of course I was in a little bit of a hurry and just ran all my grounds to random placed on the truck and borrowed power from wires and ran most of my feeds from a relay.  For the longest time I was having lots of trouble at idle, my spark was very intermittent and spirratic.  I was condemning my 6AL box for a long time.  Then one day we were watching it idle and noticed that when the electric fans kicked on it seemed to cause the funny idle.  I broke down one day and decided to completely redo my feeds and ground.  I ran all the grounds to a centralized location that went directly to the battery.  I ran my 6AL wiring straight the battery posts (just like it says in the instructions) and separated my power wires to the ones that were low amperage (like gauges and computer wires) and ran my high amperage wires to batter (like my electric fans, coil and 6AL).  I got it all together and it started right up and runs absolutely PERFECT!  My truck has never ran so good.  I can be the easiest thing to over look.  Just because a ground will light a test light doesn't mean that there is not a lot of resistance in that circuit.  My truck is almost 50 years old so that ground has to pass through 50 years of rust and contaminated metal.  So if you are having strange problems it is a good idea just to recheck the basics.  Always check you F & G's.  (Feeds and Grounds).

Robi