I drove the truck two different times that morning. No issues. Went to start it to make a PO run. No dash lights, no start, dead! Found a blown 40 amp ignition fuse. Put a new one in and it blew as soon as I put it in. Checked one side of the fuse slot it has power. The other side reads ground! Direct short somewhere? Inspected starter wire going to solenoid. Found the insulation completely gone the last 6 inches going to the solenoid. Removed starter and separated the wires from touching any metal. Still have a ground signal with my test light on one side of the fuse slot.The battery wires are OK, no damage. Replaced the one going to the starter anyway. My next plan is to disconnect the ignition harness under the dash. Anyone have any other ideas? Thanks in advance!

 

Disconnected ignition harness from underneath the dash. No luck!

 

Just verifying - fuse blows when you put it in before you turn the key on?

 

Yes! It's a direct short. So frustrating.

 

It’s unlikely to make a big difference in the wiring diagrams, but please “fill in the blanks” so I can get accurate schematics:

1998 Suburban (C or K) (15/25/35 hundred) (5.7/6.5/7.4)

Are there any aftermarket accessories that have been wired to/near the under hood fuse block, battery, instrument panel fuse block, or primary ignition wires on the steering column?

Start by removing the under hood fuse block (disconnect negative battery cable first) for inspection of the wiring underneath and to check for any rodent nests. No matter how clean the vehicle may be overall, mice can build nests and destroy A LOT of wires in a single night. That damage doesn’t disappear even if the mice run off at the first start of the engine.

Make sure to inspect the bottom side of the fuse block for corrosion, even if there’s no wiring damage/mouse nest.

If all good, get a 40 amp cycling circuit breaker with the same size terminals as the fuse. Reconnect the battery, and one at a time, pull other primary fuses from the block.

The IGN fuse is a direct battery feed via the 175A charging fuse, so if the circuit breaker stops cycling when a particular fuse is pulled, it’s likely something on that circuit is related to the problem.

One other thing to try is disconnecting whatever ground points you can easily see. I think there’s at least 2 or 3 in the engine bay (check corners). As with the fuses, if the CB stops cycling with a particular ground, those are the components/circuits related to the short.

I can advise you more accurately when I have the chassis and engine details.

 

Thank you so much for your help ! It's a 98 Chevy Suburban 1500 LT 4 wheel drive 5.7L gas eng and two batteries. The only after market item would be a trailer brake controller that was installed about 8 years ago by a RV dealer.

 

The IGN A fuse supplies power to the starter relay in the fuse block and is one of the ignition switch feeds.

Given your description of the starter wiring, try pulling the starter relay. It’s entirely possible the relay contacts/coil melted together when the wire grounded out.

 

I pulled the starter relay with no change. Also, I ohmed out the purple wire from the relay to the starter solenoid. It surprised me, but the damaged wire with the insulation missing ohmed out good?

 

Meters (digital or analog) only use about 2 volts to check resistance - it’s far from accurate when trying to assess wire condition, as you’ve seen with the bad solenoid wire.

When I’m trying to assess wire integrity, I use a 9000 series headlight bulb in place of the load. In the case of the starter solenoid, I’d connect the bulb at the solenoid end and back to battery ground - if the wire is in good condition, the bulb will shine as brightly as it would if it were receiving direct battery power. Its brightness will also remain steady as I wiggle the wiring harness between the fuse block and starter. If there’s a weak connection in the harness, the bulb will start flickering or dimming, identifying the problem area.

Obviously you can’t do that at this point because there’s a direct short to ground, but you get the idea.

Let me know what, if anything, you find while inspecting under the fuse block. Inspect the harness around the back of the engine as well and where it drops down to the starter area - lots of places for the harness to catch & chafe in those areas, especially with age.

Also inspect the wiring and connections for the brake controller. If the controller is powered by one of the red wires to the ignition switch, disconnect or unplug the controller and see if the short is gone. If so, time for a new controller (or delete it, if not needed).

 

Thank you SO MUCH for all the information! Much appreciated! I can't work on it today, but will be back at it over the weekend. Will report back with my findings.