Headlight and dash light flicker

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Considering all the things you've replaced, It's time to look for a possible bad light switch or bad connection to it.

Check your battery cables.

try checking the ground wire on the frame next to the head light if you have a volt meter measure voltage on the hot side, if there is 12 volts then measure it on the ground side, is it lower than 12 volts? if it is you have bad ground strap follow the wire it will be near the radiator core support and sand it off if that does not help then it's in the light switch.

You have a light sensor that automatically turns on your lights when it is dark enough. This is not your daytime running lights. It also turns on the dash & tail lights. This is why they do not get brighter when you turn the switch on, they are already on. If they do not seem to be bright enough, you may need to adjust the headlight aim.

sounds like a short in wire to tail light, remove tail light and check ground first, if still problem then use wire probe and traces wires until u find problem

I have over 300k miles on my 2000 Venture. When the lights start flickering at low RPM's, the alternator or battery might be going bad. I would have it tested (for free) at the local AutoZone or Napa. The alternator SHOULD last 80-150,000+ miles. Its a real pain to change out on the Venture vans.

Sometimes I wonder if the van just doesn't create enough juice to run all of the accessories since even when batery and alternator are new they flicker once in a while when a component turns on.

I get zapped year round by my cars, even in high humidity. It is not harmful, but be careful at gas stations!

do you have a alarm system malfunction? or is it a relay timer switch

2000 chevy venture run good but my lights flickers and have to jump. After I jump the van and put my meeter on the battery its reading 14.volts at idle. I can drive around to store cut the van off come out it starts fine leave it overnite and it don't started.

first of all your battery should be strapped down tight. no it sounds like you have a negitive to ground problem. if this van were in my shop i would install a jumper wire from the battery to the frame of the van just to see if this fixes the problem. that is where i would start. let me know how you turn out . and can advise further.
good luck
paul