FLHTCU Electrical Repair Tutorial
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Road Master
Joined: Aug 2007
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FLHTCU Electrical Repair Tutorial
Since I was helped so much regarding my electrical problems on my 1990 FLHTCU I wanted to post a short repair tutorial...
Here were my symptoms:
Jumpy voltmeter. It would drop down to 4 volts and jump to around 10 when the blinkers were on. Same thing when applying the brakes.
Bike charged fine, battery is fine, all cables are fine.
Radio would shut off if I applied the front brake if the RPM's were under 2000. It would turn back on when I released the front brake.
Horn sounded weak and sometimes it wouldn't even blow.
If you have any of these symptoms I think I have your fix.
#1. Disconnect positive battery cable from battery.
#2. Remove front headlight bezel (1 screw)
#3. Remove headlight assembly (around 5 screws) and unplug headlight
#4. loosen top bolt for running lights and completely remove bottom bolt on each side
#4. put some rags on your front fender and let the running light assembly rest on your front fender
#5. look up inside the headlight opening. There are 2 7/16 bolts with large fender washers on each side. Loosen them.
#6. Remove the 5 bolts and chrome bracket holding the windshield on and remove the windshield.
#7. Pull the front of the fairing straight off.
#8. Unplug the connectors for the radio along with the rear radio bracket bolt/ground and pull it out from the front. There are little spring tabs on each side of the radio that you can push in with a screwdriver as you pull the radio out. Its simple.
#9. Look for the main ground block. Its located right above the anti-dive solenoid. If you disconnect some of the wiring harness plugs and push them out of the way you will see it. Its in there fairly deep but you can get at the wires with a long needle nose pliers.
The main ground block has 8 wires attached to it. They are all connected with .250 female quick disconnects. Some of the wires are 14-16 gauge and some are 18 gauge so if you need to replace the connectors make sure you have both types of quick disconnects.
#10. Use tape or label markers and as you remove each wire from the ground block mark it so you know where to put it back. I labeled mine 1-8.
What you will notice is that either your ground block is dirty or more likely the quick disconnects are failing. They are fairly brittle and because they are responsible for ignition, lights and accessories if they aren't on those ground tabs tightly you will have the issues I mentioned. You can tell if they are failing because when you remove them, some will come off really easy. I actually found one that was loose and one that had a cracked retention tab. I replaced the suspect ones, cleaned up the block and tabs with a pencil style wire brush and reinstalled the connectors on the block. You will notice that some of these wires are heavy gauge and are main grounds directly to the bike frame.
Put everything back together BUT DON'T REINSTALL THE FRONT FAIRING YET and fire your bike up. No more jumpy voltmeter. No more radio that shuts off when the front brake is applied. No more anemic sounding horn. When you have checked everything out and made sure that everything works, reinstall your front fairing and your headlight.
If you want to know why this happens?
The radio needs 12 volts to work. Because of the dirty and faulty grounds, when I applied the front brake the anti-dive solenoid would kick on (which is one of the wires that connects directly to the ground block) and the accessory side of my electrical system would get a voltage drop and the radio would shut off. When I released the front brake the solenoid would shut off and the voltage would come back up and the radio would come on.
The jumpy voltmeter was because of the main grounds on this bar being dirty or faulty. The voltmeter relies on a proper ground in order to work properly.
The horn would not work sometimes and sound anemic because again.. it relies on a proper ground. This ground block ties all the front part of your Ultra Classic grounds to a central location. They are all on separate tabs but all 8 tabs are contained on the same block.
The service manual calls it a brass block. Mine was not brass colored. Its silver.
Here were my symptoms:
Jumpy voltmeter. It would drop down to 4 volts and jump to around 10 when the blinkers were on. Same thing when applying the brakes.
Bike charged fine, battery is fine, all cables are fine.
Radio would shut off if I applied the front brake if the RPM's were under 2000. It would turn back on when I released the front brake.
Horn sounded weak and sometimes it wouldn't even blow.
If you have any of these symptoms I think I have your fix.
#1. Disconnect positive battery cable from battery.
#2. Remove front headlight bezel (1 screw)
#3. Remove headlight assembly (around 5 screws) and unplug headlight
#4. loosen top bolt for running lights and completely remove bottom bolt on each side
#4. put some rags on your front fender and let the running light assembly rest on your front fender
#5. look up inside the headlight opening. There are 2 7/16 bolts with large fender washers on each side. Loosen them.
#6. Remove the 5 bolts and chrome bracket holding the windshield on and remove the windshield.
#7. Pull the front of the fairing straight off.
#8. Unplug the connectors for the radio along with the rear radio bracket bolt/ground and pull it out from the front. There are little spring tabs on each side of the radio that you can push in with a screwdriver as you pull the radio out. Its simple.
#9. Look for the main ground block. Its located right above the anti-dive solenoid. If you disconnect some of the wiring harness plugs and push them out of the way you will see it. Its in there fairly deep but you can get at the wires with a long needle nose pliers.
The main ground block has 8 wires attached to it. They are all connected with .250 female quick disconnects. Some of the wires are 14-16 gauge and some are 18 gauge so if you need to replace the connectors make sure you have both types of quick disconnects.
#10. Use tape or label markers and as you remove each wire from the ground block mark it so you know where to put it back. I labeled mine 1-8.
What you will notice is that either your ground block is dirty or more likely the quick disconnects are failing. They are fairly brittle and because they are responsible for ignition, lights and accessories if they aren't on those ground tabs tightly you will have the issues I mentioned. You can tell if they are failing because when you remove them, some will come off really easy. I actually found one that was loose and one that had a cracked retention tab. I replaced the suspect ones, cleaned up the block and tabs with a pencil style wire brush and reinstalled the connectors on the block. You will notice that some of these wires are heavy gauge and are main grounds directly to the bike frame.
Put everything back together BUT DON'T REINSTALL THE FRONT FAIRING YET and fire your bike up. No more jumpy voltmeter. No more radio that shuts off when the front brake is applied. No more anemic sounding horn. When you have checked everything out and made sure that everything works, reinstall your front fairing and your headlight.
If you want to know why this happens?
The radio needs 12 volts to work. Because of the dirty and faulty grounds, when I applied the front brake the anti-dive solenoid would kick on (which is one of the wires that connects directly to the ground block) and the accessory side of my electrical system would get a voltage drop and the radio would shut off. When I released the front brake the solenoid would shut off and the voltage would come back up and the radio would come on.
The jumpy voltmeter was because of the main grounds on this bar being dirty or faulty. The voltmeter relies on a proper ground in order to work properly.
The horn would not work sometimes and sound anemic because again.. it relies on a proper ground. This ground block ties all the front part of your Ultra Classic grounds to a central location. They are all on separate tabs but all 8 tabs are contained on the same block.
The service manual calls it a brass block. Mine was not brass colored. Its silver.
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