Just hoping someone can help point me in the right direction. My guess is maybe something is wrong with the ignition or shifter or something like that, because there are no signs of a bad battery, bad starter, or anything like that. Thanks in advance!
Greetings slgs_13,
Welcome to the GMT400 forum! There are a lot of Texans in here, so no doubt you
will feel right at home. :0)
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The majority of the time when the starter won't crank there's a loose connection at
the high current connections at the battery. Since we only have 12v to work with, we
need tight, high current connections to get enough watts together to make things happen.
So as thinger2 mentioned in Reply #3, make sure that your high current connections
are good. I'd hate to drag you through the crank circuit for no good reason. :0)
****
When it comes to troubleshooting No Crank problems, leaving the headlights on
and observing their behavior while cranking can be informative. One scenario is
where the lights dim a lot when trying to crank the engine over. Either the battery
can't deliver the required current, or the starter is drawing more current than normal.
On the other hand, if you turn the headlights on, turn the key to Start, and they don't
change their brightness *any*, then we know that we either have an open connection
on the power circuit, or the power circuit is good, but we have a bad connection in
the Control circuit. (Bad ignition switch, bad Safety Switch, intermittent loose
connection, flaky Relay, etc.)
You shared an interesting problem statement. Per your comments it does sound more
light a loose/intermittent connection as opposed to a weak component. Therefore, I
want to lay out everything that's involved in getting the starter to crank the engine over,
and then see what you can find. We'll use a Building Block approach, starting with the
base circuit we need to work (power circuit) ...followed by the control circuit on top of it.
Fortunately for us, the '96+ electrical layout makes sense and is well documented in the
Factory Shop Manuals. Here we go:
1) The Starter Relay is the epicenter of the Crank circuit. You are going to control the Starter
Relay via the Ignition Switch. So in the first 2 photos here's the physical location of this
all-important relay:
Take the cover off of the Underhood Fuse Block and check out the (4) large, identical gray relays. One of them is the Starter Relay.
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Take that removed cover & flip it upside down. Now you have a legend that identifies which part supports what circuit:
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So, the Starter Relay lives in the Upper LF corner of the Underhood fuse block. These relays are pretty
reliable, but by now no doubt at least a million potholes, speed bumps, and highway rumble strips have been
driven over. So the first question to answer is: Do I have a good relay with loose socket connections,
or I do I have a bad relay in a tight socket?
I'd suggest that you pull the relay and see if it puts up a little resistance to removal, or if it just pops out.
(Tighter is preferable to sloppy.) While it's removed, try to start your vehicle with the key and verify that
nothing happens. (Just verifying that you have the correct relay socket location.)
NOTE: I wouldn't swap the relays around until the no-start returns. Once the no start occurs, swap
one of the other identical relays (A/C relay?) into the Starter Relay socket and see if the problem is fixed
or unaffected. In the perfect world you catch it in the act, won't crank at all, you swap in the A/C relay,
and it lights right off. Life is good.
But what if it doesn't start? How do we take this to the next level of troubleshooting?
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So we've swapped the relay & no joy.
Stop here and make sure that the truck is in Park or Neutral. Emergency brakes on. Chocks are further insurance.
Locate the 40A "IGN A" fuse, pull it, and ensure that the fuse blades are clean and the connections in the fuse block are tight.
Still no crank? Then pull the Starter Relay, and using a short jumper, connect socket connector #30 (RED) to #87 (PPL). The
starter should immediately begin to crank the engine over. IF not, then you need to verify that the purple wire to the starter is
a nice, tight connection. And if it is, and there's full battery voltage at the end of the purple wire, then the starter solenoid is suspect.
But if the starter is working when you jumper #30 to #87, but not working with at least 2 different relays tried, then since you have
proven that the High Power path for the starter Solenoid is good, then now we have no choice but to troubleshoot the Control circuit:
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Here's the complete control path:
1) IGN A 40A fuse > 2) Ignition Switch to Start Position > 3) CRANK 10A Fuse {in instrument panel fuse block} > 4) Neutral
Safety Switch (TR switch for Autos, Clutch Pedal Position switch for manuals) > 5) Starter Relay control side (Pin #86 to #85)
...and finally, the current continues to flow to G105.
Since this is a series circuit, an interruption at any point in the circuit prevents current flow through the control side of the relay,
so no Click, no closing of switch contacts, no joy.
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So if a good cleaning session at the battery connections don't clear the fault, then locate the Starter Relay in the Underhood Fuse
Block, clean connections, watch the headlights while trying to crank the engine, and eventually the problem will be found.
Please be sure to report back with either further questions or what you discovered to be the root cause.
Happy Hunting --
