Intermittent cranks no start & voltage loss to ECM 1, ENG 1 after rain. Dash light & security work fine, not throwing codes. Please help!

[OldJimmy4.3]

2000 GMC Jimmy Diamond Edtn 4X4 with 4.3L Vortec (Vin W) with 170k miles.
Rain causes no start - cranks strong, dash lights, security & gauges on instrument panel operate like they should, not throwing codes.
It's been in the shop more than once for this, but they can't figure it out & just wanna guess with my $$$, which I can't afford, so I'm determined to figure this out myself now. If I can't, then it's time to let it go. I've owned it for 12 yrs, it's in good shape & still runs great except for this, so I'm just not there yet..... Not for this.
I'm determined to learn, so I picked up a test light, a DMM, signed up for Alldatadiy & have read soooo many threads over the past few months, but I just need a little guidance from here.
It has some old, minor front end damage & low beams haven't worked for awhile...I suspect rain enters hood where it shouldn't because I figured out that, if I cover the entire hood with plastic when it's going to rain, the problem doesn't happen. (Kind of embarrassing though & getting old fast!)

Checked with a test light during a no start & These fuses would't light it....( then did, once it would start).
ENG 1, ECM 1, B/U LP, OXYSEN, IGN E, TRL TRN, TRR TRN, TRL B/U, VEH B/U. (Not sure about BTSI fuse - I missed that one, but all the big fuses on top row still had power). After that time, I switched to checking with DMM ..same fuses show 0.00 volts during no start. (The only blown fuse I found was the LT LOW, so I changed it. It hasn't blown again...(yet anyway), but low beams still don't work : ( Twice while reading fuses, I heard a clicking/tapping...like morse code...maybe from under fuse box, or maybe a relay, I'm not sure. Doesn't happen every time & not long enough for me to find it.
The engines always starting again before I get to fuses in side of dash, but checked those when it did start - all showed battery pwr except the PARK LP fuse. It showed .02-.02, then with lights on, it fluctuated from 10.78/10.84 on both tabs?? (Less than battery voltage, but I think ok?) - Cigar lighter fuse has blown twice in past 6 mths, but is working now. I have't checked anything under dash yet, since everthing else seems to be working when this happens.

I haven't tested relays yet, but that's where I may need some help. It seems like a couple times, after jiggling them, the truck would start again before I really had the hood open long enough for it to dry out. I'm just not sure which fuses would be affected by which relay, how the trailer/back-up fuses play into this. (Cause or effect?). I also recently read to watch the tachometer during no start, so I did the last time. It twitched a little on 1st try, then nothing on 2nd and 3rd. (Reminded me of another time I had trouble getting it out of park to push it during a no start.
I've tested fuel pressure recently, when it was starting...tested ok. Got close to battery voltage on pink wire to ignition module once, but thats as far as i got that day. (Intermittent stink!). I also recently replaced battery, distributor cap & rotor but no change.
Expecting rain for next few days so really hoping for some help with this.
Thanks!

[DeltaP]

Get a wiring diagram and start tracing main wiring. Might be a damaged under hood distribution box,( fuse and relay center). May have been caused by prior front end damage and not showing up until now. Short in box, bus bar connections,etc.

[Tech II]

Possible ignition switch?

Those listed fuses get power from one of the legs....

Could also be a bad connection at the Underhood Fuse Block....

Also, when vehicle won't start, take the palm of your hand and give the UFB, a whack with your hand....

[OldJimmy4.3]

Ok, I'm off work today & storms later so good day for more testing! Appreciate the help, but remember, I'm new to all this so need specifics. Adding some addtional info that may/may not be related.

Response to Tech II & DeltaP
Tech II – That schematic you posted isn't one I've seen & doesn't show what it's for? Where are these fuses so I can check them too? Since it seems like wiggling relays may have helped before, any tests can I do with my cheap DMM while it is starting to find problems? (The lack of movement on RPM gage is something I only recently noticed during a no start & I also recall having trouble trying to get floor shifter out of park during another no start). (Other issues I have are [b]Inaccurate Fuel Guage, ABS & Service 4wd lights stay on after some prior repairs but don't think they are related)

DeltaP – I'm new to this so the term “main wiring” doesn't help me. I've looked at many diagrams on Alldatadiy, but many different sub sections, I don't know how they tie together, which to focus on, or how to follow 1 wire through them. All they helped me see was that the CRANK, ECM1, ENG1, OXYSEN, B/U LP, and IGN E, are all on the power distribution schematic for “Ignition Run and Start bus bar”.The top row of maxi fuses have power during no start, & since it does crank, I assume that the Starter Relay is fine, but can someone confirm?
(I thought it would be easy to search info to concentrate on a circuit, but with computer controlled everything & no good description of how power flows through a circuit, it's not so easy).

[b]Newer Issues - DIC Shut off - Buzzing behind stereo
Yesterday, while on freeway, the overhead DIC (drivers information center) that shows outside temp, direction & fuel info turned off for a few seconds, then came back on, & I lost sound to stock stereo. Also, a couple other times, when I shut the engine off & removed key,I heard buzzing from directly behind the stereo. It stops as soon as I open the drivers door to get out. This happens once in a great while...sometimes even with no rain & these 2 things don't happen at same times. (For while now, the drivers door lock doesn't go all the way down when i hit lock switch & illuminated entry/exit stays on until I hit the unlock switch. Same when I exit. After I get out & shut door, I have to open door again, hit the unlock switch & re-close it to get them to go off after 15 seconds - no longer have key fob). Security acts like it should during no start, so don't think it's the problem.

Relays?
I do recall going out to check after rain once, & opened passenger door to pop hood & check fuses. Same ones weren't getting power. I shut door & though I heard a click. When I checked fuses again, they were getting power so I knew it was going to start again, and it did. Makes me wonder if closing the door shook out the remaining moisture from somewhere?? A relay maybe?

Questions for more testing today?
Should I be checking this “IGN1” pink wire for possibly shorting in rain? If so, do I test at the ignition switch, or is there an easier/better place?
The DIC going out & buzzing behind stereo has me thinking maybe problem is behind dash somewhere & I'm sure there are fuses back there I should test also, but alldata isn't helping me figure out. - (I have noticed that on the firewall, along the horizontal seam, there are some stains that look like rain may be coming from behind the seam into engine compartment, so it must also be getting behind dash. Also, the fact that the no start does not happen after rain if I cover the whole hood with plastic, which I tuck under the windshield wipers & cover all the way below headlights has me thinking that too.
I really appreciate the help!

[OldJimmy4.3]

Voltage Drop Test results ?

While waiting/hoping for a little more direction (& the rain), I followed this guide for Voltage Drop testing from another thread found at this link - http://i.imgur.com/WMDprhm.jpg
None of my results were what they should be or if they may explain my problem, so I'm just more confused.

Engine off, turned headlights on for a couple minutes, then back off. Meter on 20 volts Measured 12.16 across battery posts. (It's usually around 12.40 when I check before starting w/o turning lights on).
I then started the engine, turned headlights back on and did these checks.

Neg battery post to Positive should be 14.1-14.8. -Mine fluctuated from 14.19 – 14.23
Neg battery post to Engine Block should be 0.04 - Mine Fluctuated from .24-.28
Neg battery post to body/frame should be .02 - Got 0.00 with intermittent “-” sign?
Negative Engine block to body/firewall should be .02 - Got .29, tried again, .19
(For the “block”, I touched 1 lead to the solid looking area below the large electrical connector that controls the fuel injectors & other to the firewall?)
Positive battery post to alternator output stud should be 0.3. - Fluctuated .08/.09 (checked with lights off too, .05)

Positive battery post to several fuses in fuse block should be .04 - (Says to do this test while someone is cranking but I'm alone so checked with engine running & focused on mostly fuses that lose voltage - readings are from right to left tabs on top of fuses).
ECM1, ENG1, OXYSEN, B/U LP, IGNE were all .24-.24
(Also tried with headlights off & – Ecm1, eng1, oxysen all read .19-.20 , while b/ulp & igne were.19-.19).
These all showed 14.04-14.04 -TRL TRN, TRR TRN, TRL B/U, VEH B/U, LT TRN, RT TRN
ECMB & IGNC should be hot at all times – ECMB read .12-.14, IGNC .11-.11
5 maxi fuses – INT BAT 60amp - .11-.10, ABS 60a - .10-.10, IGNB 50a .11-.11, RAP 50a .11-.11 (fluctuated from .10 -.11 on both sides), IGNA 40a .11-.12, STUD #2 30a .11-.11
Headlight fuses - Since I recently changed the blown LT LOW, I checked it & got .11-.12, RT LOW was .11-.11.

Since I was testing with the engine running, I noticed that headlights were hot while leaning on them. I also noticed a faint but fast tapping sound that seamed to be coming from the ignition control module, but don't know if that is normal?
Please translate? I know fuses should be same across both sides so I put the ones that weren't in bold. Does any of this help with my no start in rain and are there any other tests I should do? I can check wires/connections next, but just need to know which & where to access. Thanks!

[OldJimmy4.3]

Anyone?
Well before I could try to make sense of yesterdays voltage drop tests, I had another cranks, won't start this morning since I didn't cover the hood & it rained last night. (I could see water dripping down from horizontal seam along firewall again in a couple places).

I smacked tops of fuses & relays with palm of my hand, then turned the key from outside the truck so I could hear better. I did hear click of relay, & squirting sound of fuel under hood so started checking fuses. With meter to ground, key to run (readings were same on both tabs on top of each fuse, so fuses themselves are good)

OXYSEN, IGNE, ECM1, ENG1 - On all I got 12.08
The 6 fuses in upper left of box for trailer turn & veh b/u were all 0.01
ECMB (should be hot at all times) showed 12.18
Didn't write down the 5 maxi fuses but think all had power - I think 12.18 also
Negative to stud where cable connects to fuse box was also 12.18
Checked negative to positive across battery - showed 12.32 - Should fuses be lower than whats available at battery?

Since I was getting readings on fuses that usually show 0 volts when it won't start, I thought it was going to, but it didn't? That's a first!

Tested the Ignition Control Modulefollowing this site - http://easyautodiagnostics.com/gm/4....test-the-icm-2
Black lead to - battery, red to backprobe on Pink wire, I got 12.03
(Says if you get 10 to 12 volts it means fuse that feeds this circuit with voltage is OK but I guess I already knew the FUSE was ok?)

Red lead to battery +, black to backprobe on Black wire/white stripe = 12.12
(I had forgotten to turn key back on when i first checked & got 12.27 if that means anything). - Test says between 10-12 volts, means the ground circuit is OK.

The next test requires making an LED test light with a resistor to see if the ignition module is feeding the ignition coil with a Switching Signal while cranking. Since I didn't put the tester together yet & didn't have a helper to crank the engine, I didn't get to this test, so decided to try starting it & it fired right up.

What confuses me this time is why it still wouldn't start when I did see power on the fuses that I usually don't?
If I do figure out where to access that pink wire from Ign1 on my 2000 Jimmy, is it really necessary to disable the airbag? (read that somewhere)
(May be talking to myself at this point, but still trying).