Will not start there is no power to ECM/Ignition fuses but power to other fuses

BEN ZIEGERT

MEMBER
1993 CHEVROLET 1500
4.3L
6 CYL
4WD
MANUAL
160,000 MILES

My truck will not start due to electrical issues. All of my fuses under the dash appear to be good but I'm not getting voltage to the ECM-IGN fuse and a couple of others. I had just fixed a wiring issue with my headlights and now those work, but my truck won't start. Did I maybe blow the main fuse that's for ignition? Looking for a wiring diagram from the battery to the fuse block for the ECM fuse.

8 Replies

BEN ZIEGERT

MEMBER
9 POSTS

Wondering if this is a bad fusible link?

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Wednesday, February 2nd, 2022 AT 6:40 PM

KASEKENNY

MECHANIC
18,907 POSTS

That is interesting.

Take a look at the info below. I am wondering if the 3 fuses above the ignition fuse have power.

If not, then we may have an issue with the power feed coming into the fuse block for those fuses.

Basically, this is fed from the ignition switch so does anything else work when you turn the ignition on? Meaning does the radio work when you turn the ignition to the on position?

https://www.2carpros.com/articles/how-to-check-a-car-fuse

If it does then we must have an issue with the fuse block itself. As you can see from the last diagram the three fuses are tied together so there must be a break in the link between the fuses.

Run through this and let us know what you find. Thanks

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Thursday, February 3rd, 2022 AT 5:50 PM

JACOBANDNICKOLAS

MECHANIC
109,896 POSTS

Hi,

I was able to find an OEM schematic and highlight it for you. Power from the battery goes to the battery junction block. If you have power to other things, the fusible link between the battery and junction block is good.

Next, it goes from the junction block to the main connector in the engine compartment pin 2. This is another fusible link. Check for power at pin 2 in the connector. If you have no power, suspect the link.

From that point, power runs into the cab via the large connector on the cowl in a few different directions, including the ECM-IGN fuse. Note: The same power supply is for the turn signals, backup lights, and gauges. Do they work? They take power from different fuses, but they receive power from the same initial point. If they work, it sounds like the fuse box may be bad.

Take a look at the pics below. I did highlight the wiring for you. Also, here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below.

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Thursday, February 3rd, 2022 AT 6:16 PM

BEN ZIEGERT

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9 POSTS

Only have power to CTSY and Park-LPS fuses. I have power to the junction block. What's weird is that I tested continuity to see if the fuse was good and it was. Then I hooked up an m18 battery, + to just the fusible link and - on my multimeter and got voltage. I'm very confused because the wire appears to be intact but also doesn't get voltage from the battery even though it is a complete circuit. I am out of ideas at this point.

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Friday, February 4th, 2022 AT 5:30 PM

BEN ZIEGERT

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9 POSTS

There is a power drain somewhere. Maybe that is a clue? I had everything off and forgot to disconnect the battery came back today and saw it was drained. Battery is not the issue. Tried with others and the truck still drains power.

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Friday, February 4th, 2022 AT 5:38 PM

JACOBANDNICKOLAS

MECHANIC
109,896 POSTS

Based on your description, it sounds like the issue is the battery junction block. If you disconnect the battery and all connectors, check to see if there is continuity between the supply (where the battery power attaches) and the sends (where the fusible links distribute power).

Also, using your multimeter, confirm there is no continuity direct to ground from the block.

Let me know what you find.

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Friday, February 4th, 2022 AT 7:36 PM

BEN ZIEGERT

MEMBER
9 POSTS

The junction block appears to be fine. No continuity to ground. I get 12v on each terminal. Here's what I found so far to sum everything up.
-Only power to CTSY and Park-LPS fuses under the dash
-Power at the junction block, 12v on all terminals and no short to ground.
-Wire and fusible link to fuses under the dash are good (tested with meter and battery)
-Ground is good (tested with meter from the battery to different points on the truck. Cab, bed, engine bay, engine block, etc)
Any last ideas before I send it to a shop?

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Thursday, February 10th, 2022 AT 4:21 PM

JACOBANDNICKOLAS

MECHANIC
109,896 POSTS

Hi,

If the fusible link is good and there is power through it that doesn't make it to the fuse box, there is an open between the two locations. Have you checked the splice right after the battery junction box? Splice (S151) is one last place to check, and the bulkhead connector at the firewall could be open. Have you checked there to make sure there is power from the fusible link?

See pic 1 below for the splice I'm referring to. If the splice is good and the bulkhead is good, the last thing to do is disconnect the fusible link from power. Check for continuity in the wire starting at where the link gets power to the bulkhead. If there is little resistance and you have continuity, go to the inside of the truck, and do the same from the bulkhead connector to the fuse.

Let me know what you find or if you have any questions.

Take care,

Joe

See pic below.

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