Burnt Wire on Starter Relay

[Dgroshek]

Hey all, I'm new to the forum and have only had my 1990 GW for a few weeks now. Mainly taking interior parts off and stripping the vinyl for a re-spray. Tonight I fired it up after changing plugs. Ran for about 30 seconds before a fire at the starter relay (I believe). The wire seems to either go to my run or start portion of the ignition switch. Kind of confusing because 4 "green" wires lead to red wires off of the same terminal. I know it's not going to the alternator because I chased those wires back. The others went into the firewall. Haines manual says starter/ignition...

My volt meter on the dash has consistently read through the roof highline running and low while trying to start up if that means anything but the battery test while running is consistently 14.44V with nothing else running.

20230428_200208_remastered.jpg

[tgreese]

Good morning Derek.

These vehicles have three or four fusible links which can fuse if there is a major short. Look at this diagram and identify which wires are melted. https://oljeep.com/gw/elec/89GW_elec/19 ... Switch.jpg This is the 1989 diagram; the rest of the '89 diagram is present page-by-page on that site https://oljeep.com/gw/elec/GW_wiring.html as well as the 1990 diagram (which should be pretty close to the '89 - a large file though).

I would not rely on the Haynes manual for this. The parts-store books (Haynes and Chiltons) are full of errors, and try to cover too many years. Jeep published a technical service manual (TSM aka FSM) specific to each year for their service departments. These were available to customers over the dealership parts counters; they are your best source for these vehicles. Some years are available on the Tom Collins site linked above. You can also buy a CD_ROM at RockAuto or a paper copy at BJ's among other places. Use the Haynes manual for fluid capacities and tuneup settings, or perhaps as a door stop.

Charging volts should be above 12 volts. 14.4 seems healthy. The factory gauges are not super-accurate, but you can use them to watch for a change. I would expect 12 at starting and maybe pulled a little low until the alternator starts charging. A reading of say 12 volts or 16 volts while running would indicate alternator or voltage regulator failure. The acceptable range of voltage is given in the TSM.

If you go to the "full editor" you can drag and drop your pictures if they are under I think a megabyte? 800x600 is a good size to post and will be accepted by the site.

[Dgroshek]

Tim, thank you very much for the info. First off, I'll be buying a TSM/FSM from BJ's. They've taken enough of my money on floor boards, rockers, quarter panels, and an edelbrock pro flow 4 EFI so why not throw more money to them on my next order! I'm sure I'll be spending a small fortune with them in this process. Such a great resource for restoration.

Back to the blown wire. From the schematics you gave me it looks to be the wire to the ignition switch. (18GN to 10 RD) right before the "fuse"? The black rubber thing. Unable to pull it apart so unsure if a fuse is actually there or not. Is this a common problem?

I'll try to re-post the picture I initally tried to input but doing it from a phone seemed too cause problems.

My only concern with the alternator prior to this was that the gauge on the cluster read inconsistently. Volts at the battery while running have been steady 14.4. The gauge cluster meter was reading through the roof. Since this happened, I'm not sure which to believe.

I was planning on installing the Pro Flow 4 EFI soon and prior to this wire shorting, everything seemed good to go. Now questioning if I should do a full wire harness change. FYI, this will be a daily driver once restored

[tgreese]

If a wire fuses, you need to fix the problem before you replace it.

Your multimeter on the battery is the right reading. If you worry, try a second multimeter.

Looking at the diagram, find splice B2. The dashed box contains the fusible links. The 18GN wire is a fusible link, and is 18 gauge and green. The two ring connectors in that box connect to the battery cable at the threaded stud. The other side of B2 is "10 12RD" which is circuit 10 and a 12 ga red wire. This supplies power to the ignition switch.

These fusible links are specifically undersized to melt before the wiring catches fire. They protect the rest of the car from the battery. Special insulation on the link contains the melting wire and prevents setting other stuff on fire.

The links should only melt if there is a bad short. They are not meant to be routinely replaced like a fuse. Instead, they will prevent a car fire in event of a catastrophe like a wreck.

In the TSM there will be a table as part of the wiring diagrams with the circuit numbers, ie circuit 10. Each number has a short description and where to find the circuit in the diagrams.

Seems very unlike your problem is an old or worn out wiring harness. You have some other problem that's shorting the wire to ground. IMO replacing the whole harness would be jumping from the pan to the fire, and add a lot of unneeded work and expense.

Use your multimeter and some long clip leads and follow the circuit till you find the short. Unplug things as needed. Trace the wires till you find the problem. Electrical problems require systematic measurement and analysis, and you need the car in front of you. Photocopy the diagrams, measure, make notes on the copies or in your notebook. Go circuit by circuit until you find the problem.

[tgreese]

I recall those using a phone use Tapatalk for their pictures? It resizes automatically. As I recall - I'm one with my workstations and hardly use my phone.

[Dgroshek]

Tim, thanks again for all of your help. Unfortunately I have to order fusable links because every auto parts sries doesn't seem to carry them anymore. I did temporarily hook up a regular wire to test everything. With my voltmeter. Figured I needed to have it all connected to test. Electrical work has always been my worst nightmare. My last build was a '55 CJ5 with extremely basic wiring that I almost screwed up.

The B2 you mentioned either has to be the splice in the fuse link or the connection between the firewall. I found no problems throughout. Also no evidence of rat chew or stuff like that. I decided to replace the starter relay and the ignition switch (which was a pain to get to. I will not be starting the Jeep until my link arrives but the car does respond better to the "accessory mode"? I'm thinking the ignition switch was to blame.

I agree with you on using a work station instead of a phone but my computer is all the way upstairs and typing up a question while working on the car while everything is clear in my head is better than me running up and down the stairs 5 times to post accurate info.

[Johnzi10]

Be careful not using the fusible links!!! I fried my engine and instrument panel wiring harness’s doing that. 500 in parts and lord knows how many scapes and hours and blood was involved.

[sierrablue]

Instead of the fusible link you could put in an actual remote fuse on the wires, and then you could adjust what amperage of fuse you were using and everything. And if you didn't get the problem fixed the first time, you wouldn't have to replace the entire wire every time...

[tgreese]

IMO you should not substitute a fusible link with a regular fuse. This is not something you should have to replace routinely. The fusible link is basically a piece of wire, which is way more reliable than a circuit breaker or a fuse. Plus you need a very high value fuse to replace the link; not something you will have in your junk box.

The fusible link is meant to protect the car from the formidable stored energy in the battery. Not something you need to replace trivially, like a radio fuse. If you are blowing fusible links, you have a big problem that needs correcting!

You do not need to connect power to the wiring harness to find the short. First I would find splice B2 and measure resistance from there to ground. You sank a lot of current to ground which melted that link. I would expect to see an open circuit (megaohm-ish) when there is no short. If there is some low resistance (maybe tens of ohms) you need to follow the wires along until you find the short. Do this first before you apply any power.

I would also inspect the wiring from B2 along its whole path. These cars have split loom tubing for the harness, and you can pull the wires out and inspect them. Follow along on the wiring diagram with your colored pencils or whatever.

If you find a low resistance, you can start unplugging things until the short goes away. The ignition switch has a big flat connector on the underside of the steering column. If a '90 is like earlier years, the engine harness and chassis harness plug into a bulkhead connector on the firewall that is part of the dash harness. Dash, chassis, engine harnesses. Divide and conquer.

If you want, you can clip in a fuse holder between splice B2 and the battery and apply power. However, if you don't find the short first, I expect you'll go through a lot of fuses... a circuit breaker would be better, though this approach seems like thrashing the problem to me.

Use your meter, be systematic, take your time, go circuit by circuit. Don't be emotional when you don't find the problem immediately. Check your notes, read the diagram, and be analytic. Automotive electricity is simple, but there are a lot of wires. Look at one wire at a time and refuse to be overwhelmed.

It's possible your alternator has an internal short. Seems unlikely considering the connection you melted. You can disconnect the alternator if you don't otherwise find a short by measuring resistance. Look at the wiring diagram for what's connected to the ignition. Some things, like the choke heater, vapor solenoid and idle stop solenoid are powered by the ignition and not otherwise fused. Suggest you follow the path of the ignition power to all the devices it powers on the '90 wiring diagram, and inspect or unplug those.

[tgreese]

...
I agree with you on using a work station instead of a phone but my computer is all the way upstairs and typing up a question while working on the car while everything is clear in my head is better than me running up and down the stairs 5 times to post accurate info.

NP. I don't think being constantly on the internet can help you much with this problem. You need the car in front of you, and to use your meter. Also, I would not throw parts at the problem. Possible you'll score a hit, but more likely you'll just waste time and money. If the 18GN fusible link is melted, that has nothing to do with the starter solenoid. That threaded post is connected directly to the battery, and the solenoid is just an anchor point for the link.

[Dgroshek]

Be careful not using the fusible links!!! I fried my engine and instrument panel wiring harness’s doing that. 500 in parts and lord knows how many scapes and hours and blood was involved.

Definitely did not turn the car over without the fusible link and won't. Amazon should have the 18gauge link to me tomorrow. I did go ahead and get a 14 gauge one for another wire at that post going to the alternator. A previous owner used a regular wire. Prior to knowing what fusible links were, I was just going to splice a new one in because it looked janky.

[Dgroshek]

Looking through the diagrams, I could be wrong but the slice in question here is 10-1 (18GN to 12RD) Wire going from starter relay to the Ignition Switch. Page 5 shows this for my 1990.

90-StarterSystem-8W_Page-5.jpg

Page 6 shows the 12RD going directly to the ignition switch

90-IgnitionSwitch-8W_Page-6.jpg

This is the splice location diagram. To me that splice in question looks to just be the fusible link splice.

Splice Location.JPG

I will be running my resistance test but from what I've traced of the actual 12RD wire, it looks healthy. No rat chew or evidence of overheating or rubbing. So if the wire itself is good, my only thoughts are 1. The bulkhead connection or 2. The ignition switch was faulty. I still have my old switch so I'll be testing resistance on that first.

I should mention I do plan on resistance checking everything I can to make sure the rest of the harness is in working order especially since everything is torn apart currently. Easier to get to and I can make a list of what I need to work on.

[tgreese]

The change of wire gauge is telling. Fusible links are much smaller than the wire they protect (minus 6 here, 12 vs 18). Pull on the melted wire - a melted link is crumbly/crackly inside the insulation. They don't melt in two; the insulation is designed to contain the melting wire. Possible it could still have continuity after it cools off.

The 12 ga wire should look good - it's protected by the sacrificial fusible link. Does not tell you anything.

Was the ignition on? If so, the only connection to the ignition switch that is not fused is circuit 12 14OR (orange). This could be the choke coil connection I mentioned above.

Do you understand the switch diagram? With the key on, every dot marked "RUN" is connected to power.

Figure 6 is of an MJ or XJ, not your GW (an SJ by this time IIRC).

[Dgroshek]

I will be checking the choke coil as well; already on my list for this afternoon! As well as taking the alternator off and getting it tested. The car did come with a new alternator in a box so I'm definitely not ruling out an internal regulator going bad.

Yes, the ignition was on when the wire blew. Car ran for maybe 20 seconds before the fire.

Figure 6 came from the '90 Jeep manual at oljeep. This is the only diagram that shows 10-1 and there is a note in that grouping stating that splice 10, 10-1, 10-2, and 10-3 are for all models.

[tgreese]

Why do you need that picture?

Suggest you bend and pull on the fusible link. Suggest you follow the orange wire.

[Dgroshek]

Why do you need that picture?

Suggest you bend and pull on the fusible link. Suggest you follow the orange wire.

I know for a fact it was the fusible link that blew. That's why this thread was started. I didn't know it was a fusible link and needed help tracing it.

Last evening I pulled the alternator and got it tested. It came back good, but when the guy at AZ was taking it out, the BAT terminal fell out of the alternator. Replaced it with a new one because I didn't trust it.

Tried following the 12 14 OR and still need to do more searching and found that the electric choke was replaced with a manual choke. I knew about this but didn't think to check wires prior to purchase. I can't locate the electric choke switch which may have been deleted. Will be searching for the wire this evening. The picture below shows what I believe to be 27 14 BL*. It could have hit the coil or valve covers but I haven't found any evidence of spark. Either way I think it's safe to assume I can cut an cap this wire?

20230501_195029_resized_1.jpg

The two pictures below show wires going to the AC compressor that are definitely an issue. The circle terminal shows evidence of spark on the compressor. I will be addressing these wires too. I know the AC compressor also utilises the 12 14 OR wire from the ignition but it goes through a fuse so I assume this probably isn't the reason for the blown fusible link? It should've blown the 25 AMP Fan/Heater fuse shown in SJ 6? Looks like the two wires from the AC compressor are a ground and 32 18 OR* running to A/C Low Pressure Switch.

20230501_195037_resized_1.jpg

20230501_195413_resized_1.jpg

Wiring diagrams for reference. SJ 6, SJ 8, and SJ 31

SJ 6.JPG

SJ 8.JPG

[Dgroshek]

SJ 31 here. For some reason I couldn't post in the above comment

SJ 31.JPG

[tgreese]

The choke switch is an oil pressure sensor. The choke normally is thermo-electric, and requires heat from both the choke heater tube in the intake manifold (warmed by exhaust gas passing through the manifold) and the electrical connection. The electrical connetion is only made when the engine is running, ie there exists oil pressure.

If present, the switch is located on the oil pump cover, down by the oil filter. Here's one for my J20 - this is typical. https://www.rockauto.com/en/moreinfo.ph ... 88&jsn=475
The correct part for a '90 may be NLA. Suggest you look up the part number in the 88J parts book on the Tom Collins site and search online if you are interested.

The choke connection is "14 BL*" ... does an asterisk mean trace on your diagrams? A trace is a stripe on the wire, as seen in your picture. There should be a legend somewhere with that info. I would expect blue to be BU not BL, but BK is also there and that's clearly black. Suspect that dangling wire next to the choke originally went to the choke cover.

The ring terminal looks more like a ground connection to me. Dunno ... you should trace (follow) those wires to a point where you can identify them.

I would think the air conditioning connection would not have melted the link. That part is protected by a fuse. Only the orange wire at that splice does not have a fuse.

There are other wires on this diagram that are not protected by fuses. "13 14VT" (violet) goes to sheets 2 and 17. "11 14 YL" goes to sheet 7.

[Dgroshek]

Tim, the asterisk does mean tracer. It's a blue wire with white line.

I think I figured it out. Will obviously be testing more stuff BUT...

I located the #12 splice on page SJ8. It branches off into 3 directions.
1. Electric Choke Switch (does it go into the engine block behind the alternator?) 0 resistance and connectivity buzzer went off
2. Carb Solenoid. Bit of resistance but connectivity buzzer went off. The wire is missing insulation on a decent chunk of it. Replacing that.
3. The diagram doesn't show it, so someone must've messed with it at some point. The # 12 splice does look factory though. Goes to the AC compressor with high resistance. Connectivity though. Insulation stripped off. Evidence of spark.

[tgreese]

... does it go into the engine block behind the alternator?) 0 resistance and connectivity buzzer went off

Yes, it's next to the oil pump cover, and into the corner of the engine block next to the oil filter. There should be a tee screwed into the block with this switch and the oil pressure sensor.

The switch shows three tabs; likely this includes the common connection, and one NC connection and one NO (normally closed and open resp.) You would use the connections shown in the drawing, which will be the common and NO tabs (open with no oil pressure).

With a manual choke, you could remove that switch and plug the hole. 1/8" NPT. Be sure to tape off the wire, for obvious reasons.

There are two solenoids on the carburetor.

One solenoid is normally open and vents the float bowl into the FTVC canister when the engine is off. Apply power and it closes, and the bowl is then vented from the air horn into the air cleaner.

The other solenoid is an idle stop solenoid on the throttle linkage. When powered, the pin sticks out and holds the idle at the proper speed. When off, the pin withdraws and allows the throttle plates to close completely to prevent run-on (dieseling).

That ring connector is likely the ground shown in SJ8 as part of circuit 99. It also provides a ground for the 4WD indicator (though I wonder why they would bring this ground all the way to the top of the engine).

Possible a PO took the ground connection and used it as a current source to force the air conditioning compressor on? That still goes through the bowl vent solenoid, and would not pass enough current to melt the link.