If you tested the BUS wires and did not get around 2.5v then it could be a BUS issue.. The BUS wires are the two wires that all the modules use to "Talk" to each other.. A shorted wire or module could cause this issue.. If you have a scantool perform a module scan and see which ones are dead on the BUS..
Here is a case on your issues:
Vehicle IssueThe gauges drop out at times, there are multiple CCD bus codes in many modules. 1996-2000 NS.;This case is not to be confused with an issue where solely the gauges are LOCKING UP (needles stuck, prndl and odometer half lit). This condition is for a multiple CCD bus failures. If the ccd is corrupted it can cause multiple symptoms including: PRNDL boxed, odometer may read NO BUS (1999 +) All the gauges drop out and many ccd driven lights will come on Car will not start due to vtss (if equipped) The overhead and HVAC will have an erratic operation. Please verify that your problem IS NOT JUST one isolate concern opposed to multiple system problems. Some of the most common ccd codes are as follows: MIC: no AECM message BCM: no cluster message, NO SBEC (pcm) message, NO EATX (tcm) message PCM: No BCM and TCM message, TCM: No PCM (sbec) message AECM: no cluster message. You may or may not all of these codes, just be sure its more than a one or two that are not related to the SAME module (ex. The loss of the PCM will cause pcm communiaction message is many modules, but its one module at fault (pcm)).
System or ComponentErratic Operation / Fluctuates,Inoperative;Customer Concern (No DTCs),DTC / Error Message;Gauges,All Warning Lights;Interior;Acceleration;Came From Another Shop;Yes - Intermittent,Yes - Continuously,No - Condition Never Duplicated
RecommendationOn the 1996-2000 NS vans, usually the ccd bus shorts out at the b33-e36 connector underneath the battery; battery acid gets into the 10 way connector. Keep in mind the gauges will fail because of a ccd bus that: shorts to ground, shorts to power or shorts to each other. This can be accomplished at a connector, ccd module, or anywhere in the wiring. I know this does not narrow the possibilities. Use the NS manual and see the bus diagram in section 8w-30, note all the modules on the bus. Besides the b33-e36 connector the other likely areas are G300 (bcm ground), G104 (cab ground), g200 & g201 (hvac ground), or the HVAC or CAB module. Check to see if the battery looks NEW, if so then this may also indicate there may been a bad battery that boiled over.