This article explains, in detail, how to replace the horn on a 1998 Mercury Mountaineer.
Things You'll Need
- 1/4 inch drive socket set, SAE
- 3/8 inch socket set, SAE
- Slip-joint plier
- New horn assembly (OEM or after-market compatible)
- Length of copper wire, preferably with alligator clips on ends
- Helpful things, but not necessary:
- Jack, jackstands and chocks
- Flashlight or droplight
- Circuit tester
First, make sure absolutely that it is the horn that is broken. Open the hood and stand on the driver's side while someone pushes on the horn switch. Each time the switch is pushed, you should hear a soft popping sound from the relay box. If you do not hear anything, check the fuse! According to the manual, it is fuse number 10 in the main box, located under the hood on the driver's side, right behind the brake cylinder. If the fuse is good, check the horn relay, located in the same box as the fuse. You can do this with a tester, but I recommend simply replacing it...cheap part.
If you hear the popping noise, then the fuse and the relay are okay. Next, chock the rear wheels, set the parking brake and turn the steering wheel all the way right. This gives you maximum access to the horn unti location. For better access, jack the car up a few inches as well.
Using a 5/16 inch socket wrench, remove the two screws that hold the forward wheelwell splash guard in place. pry the splash guard back toward the tire, using string to hold it back if necessary.
The horn unit is located just above and forward of the wheelwell. There are two horns; one low pitch, the other high. Now test the power wire to ensure there is power to the unit with your multitester or light, if you have one. If there is no power, then the wiring is bad and must be replaced. If this is the case, I recommend hiring an auto electric shop to do the work. Once you have determined that there is power available, now check the connection itself, make sure it is clean. Reattach it and test the horn again. Check the connector wore beteween the two horns. If the unit still does not work, proceed to the next step. Leave the power supply wire unattached.
Okay, so the problem at this point is most definitely the horn unit itself. Now we'll remove it and put in the new one.
First, you must disconnect the battery. The horn unit mounting bolts are located below the battery pan. Use a 5/16 inch socket or wrench to loosen the battery terminals, starting with the (-) ground. CAUTION: DO NOT GROUND A TOOL OR WRENCH ACROSS BOTH BATTERY TERMINALS! Using a 5/16 socket on a 6 inch extension, remove the retainer block on the inboard side of the battery. Remove the protective battery cover. Remove the battery, but keep it nearby, as we'll need it to test the new horn.
Using a 1/2 inch socket, remove the two screws and one nut that hold the battery pan in place. The nut is forward, and you may want to use a u-joint adapter to remove it. Use pliers to remove the plastic hold-downs for the battery cables. Don't cut them, as we'll need to reattach them. remove the battery pan. This takes a little finagling, but it does eventually come out!
Locate the fasteners for the horn unit. You will most likely need an extra set of hands here, one to hold the unit and another to remove the screws. Use a 3/8 inch socket. One is a screw and the other is a nut with attached washer. Remove the horn unit and examine it. Test it one more time by holding the power connector against the (+) pos battery terminal and using a small lenght of wire to connect the metallic body of the horn to the (-) neg terminal. If nothing happens, then we'll continue. If the horns sound, you had a bad ground. Clean the area where the metal body of the horn meets the metal it is bolted to and replace the unit. Try some WD-40 before you tighten the bolts.
Remove the old horns from the mounting bracket and put the new horns on in the same configuration. Pay attention to the wiring on the old unit and duplicate it as best you can. Make sure your connectors are clean and bright before you install them. For the more electrically-inclined, you can solder the wires together and use heatshrink around the connection.
After the unit is assembled, test it by holding the metal bracket to the (-) terminal on your battery and use a small length of wire from the power connection to the (+) terminal. Both horns in the unit should sound (you may want earplugs for this step!). If they do not, check all your connectons. Dissassemble the unit and try each horn seperately. Double check all your connections. Make sure the battery is charged.
We now have a working horn assembly, ready for installation. Install the unit in EXACTLY the reverse of the way you removed it, with one exception. When the battery pan is in, do not tighten the bolts. Connect the battery and test the horn. This will save time in case the unit is poorly grounded, or there was damage to the wires during installation. Once you have determined that the horn works, disconnect the battery, finish installing the battery pan. Replace the battery, battery cover,connect it and don't forget the battery retainer block. Reattach the battery cable retainers to the battery pan. Reattach the forward wheelwell splash guard flap. Lower the vehicle and remove the chocks. Check under the hood to ensure no loose tools were left there. Test the horn again. Finished!
Tips & Warnings
- have a helper, it makes it much easier
- Wear safety glasses, especially when working under the wheelwell. Lots of junk falls on you.
- If you jack the car up, make sure you chock the rear wheels, set the brake, and use jackstands.
- Wear hearing protection when testing horns.
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