1997 80-Series LC Electrical Components Not Working After Engine Rebuild (1 Viewer)

[JTinNM]

Greetings,

I recently had the engine rebuilt on my 1997 80-series LC. The engine is running great but after being installed I'm having some electrical issues:

My interior lights aren't working (ignition cylinder light, dome lights front ,center and rear, courtesy lights on doors and vanity lights on visor mirrors), additionally, my digital clock, radio/CD player and power antenna are not working. All these run through the 10A Dome fuse in the engine compartment, but it is not blown. Any thoughts where else I should be looking for the source of this problem?

I have also looked at the 15A CIG fuse b/c it reportedly regulates power to the digital clock, radio and antenna but it's not blown either.

I appreciate your input.

 

[Malleus]

First, do you have a copy of the service manual and EWD? If not, download them from the Resources section.
Second, check the connections from the engine compartment fuse block to the dash. The details are in the first sections of the EWD.

Without seeing it, or more information about how the engine was removed (not installed, but removed), it's hard to say more.

 

[cahill]

Only thing I can add is to make sure you actually test the 10A fuse for resistance. It may pass visual inspection but fail to actually conduct electricity.

 

[JTinNM]

First, do you have a copy of the service manual and EWD? If not, download them from the Resources section.
Second, check the connections from the engine compartment fuse block to the dash. The details are in the first sections of the EWD.

Without seeing it, or more information about how the engine was removed (not installed, but removed), it's hard to say more.

First, do you have a copy of the service manual and EWD? If not, download them from the Resources section.
Second, check the connections from the engine compartment fuse block to the dash. The details are in the first sections of the EWD.

Without seeing it, or more information about how the engine was removed (not installed, but removed), it's hard to say more.

Hi Malleus, I do have a copy of the factory service manual. I have owned this 80 for over 20 yrs and there is not much I haven't touched on it, but the electrical system is something I have not any troubles with until the engine reinstall. I have reviewed the FSM and it addresses trouble shooting specific electrical components but I believe this might be a bad connector that is causing all the above issues. Is there one connector coming from the 10A Dome fuse that connects these problem components? If so, do you know where it is?

 

[JTinNM]

Only thing I can add is to make sure you actually test the 10A fuse for resistance. It may pass visual inspection but fail to actually conduct electricity.

Thanks I'll do that.

 

[60 toy ota]

use a test light or multimeter to see if you actually have voltage on the load side of the fuse. That will tell you if the problem is upstream, downstream, or right at the fuse. You could also take a known live (fused) wire and apply it to the load side fuse terminal and see if it restores power to those lights. I have also seen and heard of instances where these terminals do not squeeze the fuse tight enough to secure a good connection.

 

[JTinNM]

use a test light or multimeter to see if you actually have voltage on the load side of the fuse. That will tell you if the problem is upstream, downstream, or right at the fuse. You could also take a known live (fused) wire and apply it to the load side fuse terminal and see if it restores power to those lights. I have also seen and heard of instances where these terminals do not squeeze the fuse tight enough to secure a good connection.

Good advice, I'll do that.

 

[fjbj40]

I thought the fusible links add to this circuit?

Doing an engine removal and reinstallation could certainly lead to damaging them.

 

[Comet]

Check the multiple ground connections both on the engine and the body/frame too. I remember reconnection quite a few of those on my refresh.

 

[ajax1]

I would also say check fusable links

 

[JTinNM]

Only thing I can add is to make sure you actually test the 10A fuse for resistance. It may pass visual inspection but fail to actually conduct electricity.

Good call, a visual inspection showed the 10A fuse to be good but a continuity test revealed it was bad. I replaced the bad fuse with a new 10A fuse and it blew in less than 30 seconds.

Prior to replacing the bad fuse a voltage test indicated it was receiving 14 volts (positive multimeter probe on left side of fuse and negative on vehicle ground). Can I glean from these tests that the problem is downstream, with a connector/connection?

 

[fjbj40]

Good call, a visual inspection showed the 10A fuse to be good but a continuity test revealed it was bad. I replaced the bad fuse with a new 10A fuse and it blew in less than 30 seconds.

Prior to replacing the bad fuse a voltage test indicated it was receiving 14 volts (positive multimeter probe on left side of fuse and negative on vehicle ground). Can I glean from these tests that the problem is downstream, with a connector/connection?

Voltage means nothing. Load test it such as a test light.

 

[Malleus]

From the EWD:

 

[Malleus]

Hi Malleus, I do have a copy of the factory service manual. I have owned this 80 for over 20 yrs and there is not much I haven't touched on it, but the electrical system is something I have not any troubles with until the engine reinstall. I have reviewed the FSM and it addresses trouble shooting specific electrical components but I believe this might be a bad connector that is causing all the above issues. Is there one connector coming from the 10A Dome fuse that connects these problem components? If so, do you know where it is?

This is a bit of a journey:

 

[Malleus]

 

[Malleus]

So for each and every one of those loads, you'll have to run down the harness connections from the location pages and then the specific connector housing, from the section containing that circuit. For example, from the chart, the first load is the Auto Antenna Control Switch (A21). pages 78 and 118. But you want to start with page 24, Electrical Wiring Routing, for the switch (A21):

then go to the circuit (page 78; it's actually on page 79 - this is a two page circuit diagram) :

Then you have to go to the junction pages to get those connector housing pinouts; start with the close connectors (I16 and IF1- page 32) and work outward from there:

Notice the splice points are listed in octagons and the joining connectors in rectangles. The grounds are inverted triangles; this format is continued in the circuit diagrams, too. Also, you need to look at the connectors housings at eh end of the circuit diagrams for that information, before you leave that section:

This particular connector housing has six cavities, but only two are used (1 & 6) for the antenna (someone else has 3, 4 & 5). Cavity (2) isn't used at all.

This isn't necessarily where I'd start chasing down this suspected short (I just picked the first item in the list, for convenience sake), but this is the procedure. You have to do this for each and every load in the dome fuse circuit, if you want to find the problem.

Of course, this is what you would do if someone brought the truck to you and just told you there was a problem and left it with you. You have the advantage (hopefully) of having been there when the work was done, so you should have a good (or better than average) guess about what the root cause might be.

This is why I asked what was done when the engine was pulled, and not what was done when it was installed. The most likely root cause is unkind disassembly, because it's generally easier to break something down than it is to reconstruct it.

 

[Malleus]

Another possible approach is to inspect the common ground points. For example, using the A21 circuit above, the ground is IE (through Junction J4):

So there is also a ground circuit chart:

So now you know everything that shares ground IE. If all of those loads are failure points, the problem is very likely that ground. If only some of those loads are failing, then you have to assume the ground is OK, because if it wasn't none of them would work. Electrical troubleshooting is often a case of finding what is working, rather than finding what has failed, and finding the failure by elimination.

Pages 4-7 show you how to interpret all the various symbols you'll see in the EWD. Very useful.

 

[Malleus]

Unfortunately, you picked the most popular fused circuit to hate you. But look at it this way, when you're done, you'll really know the system.

 

[Malleus]

Here is an illustrative example of what you're physically looking for (sometimes this is easier to visualize than the list of junctions, grounds, etc):

This is page 82, and you'll see there are a fair number of junctions for just this one part of the circuit, in this area. The numbers next to the rectangles, load symbols, etc., are the cavity position for that wire in the connector housing. Of course, these should only be one wire color into or out of the housings, so it isn't strictly speaking necessary to know, unless you're replacing a connector housing.

None of this is very hard, it's just really tedious. You have to be methodical in your approach, and take very good notes, or you'll be playing in traffic with a blindfold on.

 

[JTinNM]

Here is an illustrative example of what you're physically looking for (sometimes this is easier to visualize than the list of junctions, grounds, etc):
View attachment 3750814

This is page 82, and you'll see there are a fair number of junctions for just this one part of the circuit, in this area. The numbers next to the rectangles, load symbols, etc., are the cavity position for that wire in the connector housing. Of course, these should only be one wire color into or out of the housings, so it isn't strictly speaking necessary to know, unless you're replacing a connector housing.

None of this is very hard, it's just really tedious. You have to be methodical in your approach, and take very good notes, or you'll be playing in traffic with a blindfold on.

This is terrific Malleus, thank you for taking the time to explain this to me! If you are ever in New Mexico please let me know.