Factory Radio Help Needed (Power, No Audio)

[Dryicekills]

Hey guys. I’m having a real struggle trying to finalize the dash harness swap in my 88 MJ. The old one was really shot, lots of melted wires. Got a fresh one that has zero visible flaws, and with a bit of help, spent yesterday getting the dash out and swapping it out. Everything went smoothly. Truck fired right up, all lights and gauges work. All that’s left is to get this radio working. The old harness had been cut to use a Pioneer head unit. It worked just fine, so I do know that all speakers are functioning. This new harness was cut to add in some unknown radio connector, but it was eventually returned to factory (all wires are the correct colors on both sides of the splices, which seem to be done well enough). To accurately depict what is happening, I’d recommend just watching the video I’ve linked here. Also attached is a picture of the radio label, which may help a more savvy person distinguish whether maybe there’s some wiring difference between my truck and whatever year XJ I got this radio from. Also annoying is the fact that I can’t tell if this radio is even fully functional, or if I need to look elsewhere for the answer. If anyone has advice, I’m all ears. Thanks! 

 

Radio Demonstration

 

 

 

[JYau]

I have done pretty much the same exact thing as you in my 88 MJ. However, my radio that I installed was one from an 87 Grand Wagoneer, the one with a digital tuner. Since the truck had an after market Alpine head unit, the wiring harness was modified and I had to splice the factory one back in. But before I did the install, I had tested the Grand Wagoneer radio to ensure that it worked as expected. I had bought the radio on eBay, and it wasn't tested so I took a chance. Depending on the year of the donor XJ, I would not rely on color codes to rewire, I would carefully look at the pinout diagram and make sure you understand which pin is what. 

 

To test the radio, all you need are a few simple tools and a 12V power source, this could be a 12V battery but caution is needed as a battery isn't fused. Follow the sticker label on the radio for the pin functions. You typically hook up the 12V to the 12V pin and sometimes there is an ACC pin that is needed as well. Then you can take a speaker, ideally a 4 ohm one for car audio but 8 ohms will work just don't turn the volume up high, and test each audio channel output. With a few feet of wire, a wire stripper and a few wire alligator clips, you can test the whole thing out. If everything works as expected then the issue is with the truck side of the wiring. 

 

If the radio passes the test the next step would be to test the connector that you spliced back in. This would require a voltmeter to ensure that the proper voltages and impedances exist at the connector itself. Start the truck and verify you measure 12V at the 12V pin, turn the truck off and measure across the speakers and verify you see ~4 ohms. Check the grounds and verify they have a good connection. Verify your chassis is actually chassis. 

 

From your video the concerning thing is that the LCD clock goes out when you ground that chassis wire. Something is upset when your touching the ground wire. The bracket that the radio unit rests in while installed in the dash should be connected to chassis, does that cause the same behavior? How bad was the melted wiring, did you eradicate all of the melted wires? You might have some other wires that were melted and shorted but you haven't found them yet. If you don't have a multimeter your going to be guessing and checking and potentially damaging your radio in the process. A multimeter is the first tool you'll need to figure this out. 

[Salvagedcircuit]

Here is the 1988 electrical manual:

 

I spent a bunch of time with a multimeter rewiring my radio as the previous owner butchered the harness. Mine also had a melted black ground wire. I ended up pulling the wire out of my entire wiring loom, all the way to the ground point because it melted through the insulation and fused with neighboring wires. I also discovered more duct-tape crimps than I ever imagined possible.

Duct-tape crimps were factory crimps. Usually 2-7 18awg wires crimped around a brass ring then covered with duct-tape. Sometimes the crimps corrode and need to be cut and re-soldered. A lot of mine were luckily ok, so I opted to add flux and solder over them. I also added liquid electrical tape and electrical tape to seal them. It's a tedious process, but it prevents future nonsense. My '88 had duct-tape crimps. It's possible that 89+ did not have these.

The good news is that metra still makes both the vehicle harness side, Metra 70-1002, and the mating harness, Metra 71-1002. You can restore the MJ back to the factory connector and make an adapter to a new radio so it's never a problem in the future if you want to change your radio to a different brand.

[AnotherOldJeepGuy]

I second the input from @JYau, I would go ahead and confirm the radio is functioning correctly independent from the Jeep connections, you need to know the radio is or is not causing the problem.  I got one of these so that I could test radios withing installing in the vehicle (https://www.ebay.com/itm/145914455649), was a good tool in my case.