1986 c7000 box truck 366 engine won't start

[primemover]

I was having trouble uploading photos (too big). Here are the other three.

[bd]

The absence of a wiring diagram will slow this down a bit.  Nonetheless, you measure B+ (12.6 volts) on the red wire, correct?  What do you measure on the red wire when the harness connector is plugged into the ignition switch and the ignition is turned on?  Does the red wire continue to measure B+?

[primemover]

OK. Now we are at the problem I had when you suggested that before. With the switch installed, I can't seem to get access to the red wire (or any of the others) to measure voltage. The ends of all those wires are well protected by the terminal block that mates with the switch!

[bd]

HaHa!  Reminds of a song sung by Harry Bellanfanti in the 1950s, "There's a hole in the bucket...."

You have at least four choices: 1) fabricate short, 14-gauge wire jumpers using bare terminals that insert between the connector and the switch, then probe the bare terminals, 2) use a terminal tool (image) or pocket screwdriver to depress the locking tabs on the backsides of the terminals to remove the wires from the connector and plug them directly to the ignition switch, 3) force the meter probes down alongside the wires in the connectors until you make contact with the terminals, or 4) pierce the wire insulation with the sharp point of the test lead (not a problem, since inside the cab the wires are protected from exposure to corrosive elements - though, not a good idea for wires exposed to weather and road salt outside of the cab).

[primemover]

Fantastic! Now, I'm learning stuff:) Some that I can use on this project, and a bunch for other applications. Oveer the next few years, I might even get some things done in less than a week:)

[primemover]

Yup, definitely a hole in this bucket -- with a very circuitous path to understanding how to find it:)

Terminals removed from block and attached directly to switch. No voltage now at red wire, either with switch on -- or off! New (possibly misleading) symptom. Thinking maybe I left the battery disconnected when last here, I went around and _opened the hood_. Voila! Loud buzzing noise!! Sounds like ignition is on. Yup, ignition in on position. I have 12.7 volts on red (ignition off), 11.8 volts on red (ignition on), 9.6 volts on red (switch in start position) with starter motor turning over.

I like what I have, but what did raising the hood have to do with power to the ignition switch (if anything)?? [I love internittent electrical faults~:(]

[bd]

Does the truck have an alligator hood or tilt?  Are there one or two long terminal strips on the firewall?  Post an image of the engine compartment firewall on the driver side.  Have you removed the starter heat shield and checked the battery cable and solenoid connections yet?  When you do, inspect the phenolic end-cap of the solenoid for evidence of heat damage and deterioration around the battery cable connection, especially if the cable was loose.  If the battery cables are original, replace both with 00 copper cables - terminal ends securely crimped, soldered and shrink sealed.  Do not use battery cable ends that attach to the cables with a metal strap and two bolts.  Be mindful of routing new cables away from high heat sources such as the exhaust.

[primemover]

Lots to reply to:) Here is a start.

Alligator hood -- hinge partially visible in one photo.
Two long terminal strips -- visible in same photo with labels on plastic flap (cover).
Heat shield not yet off. Comments taken under advisement for when it is.

[primemover]

How about those pictures I can never remember to attach on the first message:(?

And there is a partial view of the other hood hinge in the final photo.

[primemover]

one more try on that last photo

[bd]

Since the problem is intermittent...

Check/replace the battery cables and inspect the cable end connections and solenoid as previously described.  Disassemble and burnish the Upper Block terminal strip connections 2, 3, 5 and 7 then reassemble with antioxidant (e.g., Truck-Lite NYK-77 Corrosion Preventive Compound or equivalent).  The preferred Truck-Lite product should be available at most commercial truck dealers and truck stops.  Otherwise, pick up some GB Ox-Gard from your local hardware/electrical supply.  Don't waste your money on the clear dielectric compound available from the local auto parts store.  It's not as effective.  Check the cab and frame grounds.

IIRC, there is a fusible link jumping between two of the power terminals.  The length and gauge of that link is crucial to calibration if the truck has a factory ammeter.  If any of the terminals are suspect, be sure to mechanically crimp, 60/40 rosin solder and shrink seal the replacement terminals.

[primemover]

Thanks Rich,

This plus the starter access and terminal clean-up (plus finding and cleaning grounds) will keep me busy for a day or two, this week:)

Gene

[primemover]

Companion problem: No gas to carb (carb seems to be dry after cranking for better part of a minute -- choke on). Mechanical pump on engine. ~5 gallons of fuel in tank. New filter(large canister between tank and pump. Any thoughts?

[bd]

With the battery fully charged, use a test gauge to check fuel pump vacuum (>20" Hg), pressure (~7 PSI) and volume (typically ~1 Qt in 20 seconds of cranking).  Does a drop of engine oil from the dipstick hold its circular shape on your fingertip or does it quickly track outward along your fingerprint?  Dual saddle tanks?  Some MD configurations had an electric transfer pump in the secondary fuel tank.  Make sure it works.  Check the condition of all of the fuel lines.  In rare cases, the fuel standpipe will develop a crack near the fitting at the top of the tank, causing it to draw air.

[bd]

Incidentally, five gallons of fuel may not be sufficient depending on tank capacity, especially if the fuel was added to the secondary tank.  Check the condition of the o-ring on the f/filter canister.