damn! had this and forgot about Malcolm's info!...
Ground Wire Upgrade, using O Gauge Welding Cable in an 86
Source: by Sixlitre (Malcolm H, Eddie Bauer)
"Using "O" gauge welding cable I ran it back, tie wrapped inside the frame, to a common grounding junction which also connects to the negative post of the battery. No more grounding interuptions !"
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Ground Troubleshooting, using a DVOM, Ford
Source: by Marlowe P at asashop.org
"The only two things that can cause this problem are a faulty PIP sensor or a poor ignition ground. The PIP sensor was new so it was probably OK. I asked the technician to back-probe the bottom wire on the module's connector (ignition ground) to check the voltage while cranking. It read 4 VDC! The bottom wire of the module connector gets its ground from the engine through the module and distributor. The PIP sensor uses this ground to pull PIP low, to zero VDC.
I asked him to attach the positive lead of his DVOM to the engine block and the negative lead to battery negative, and then to crank the engine while looking for voltage. Sure enough, he had 4 VDC at the engine block! Because of this, the PIP voltage could only cycle from 10.5 VDC to 4.0 volts. The fact is, with a poor ignition ground, the module doesn't charge the coil. The result is a no-spark condition.
What we found was a voltage drop between the battery negative post and the engine block due to a poor connection between the block and the battery negative cable. With the starter engaged and loading the battery, the poor connection was adding a major resistance to the circuit.
Then I asked the technician to run a jumper cable between the engine block and battery negative. I heard the engine roar to life. The technician told me that before fixing the no-spark condition, the vehicle also had problems with the starter dragging. But no more! "
Ground Article, Ford
Source: by Richard M at motorage.com
Ground Bus Info & pics in an 83
Source: by Seabronc