from the ecu there are two wires that connect to the distributor. one is brown and other is white. they are both negative( used test light) when i touch the white wire when its running, it shuts off unless i pull the test light off in time enough to keep it running. what is causing this...is it grounding out?

 

Yes... And if it's hooked up backwards it will idle but run bad else wear...
And its not a good idea to test those with a test light... The Factory book can explain this easier that it is to go threw it here....

 

Please ask the REAL question? What is it that you are doing and trying to fix.

That is not the way to test these. Please go over to MyMopar and download the 72 or 73 shop manual for cars. (I don't believe there are any for pickups) Read section 8

There are basically two ways to test the pickup. ALSO bear in mind that a BIG problem with pickups is "other stuff"

Examine the interior of the distributor. Check the shaft for excessive play. Examine the pickup and reluctor for strike damage, and heavy accumulation of rust and magnatized debri.

"Work" all ignition connectors in out several times, to scrub the terminals, and to "feel" for tightness, and ESPECIALLY do this with the distributor

Get yourself a brass feeler gauge and set the gap at .008". That's inches, not metric

Set your multimeter to low AC volts. That's right, AC. Spin the distributor or crank the engine, with the meter hooked to the distributor leads. The thing should generate about 1V AC

Check the dist. connections for resistance. Should be infinity to ground, and show continuity across the two. Resistance seems to vary a lot, but anywhere from 200-800 ohms.

Dismount the ECU, scrape around the bolt holes on the firewall and the ECU, and remount tight with star lock washers. The ECU MUST be grounded. MUST