Fratto
06-26-2021, 05:34 PM
In a previous post, I mentioned that our 2003 wrangler developed a short that blew fuse 27 serving the MFSW (Jeep code for blinker switch) and fuse 2 for the brake lights.
This must have happened on the way to the bus as the blinkers and brake lights were not working upon arrival. With no time to trouble shoot, I did not realize that we had two blown fuses and simply hoped that it was a relay or switch and that the jeep "trailer" wiring was not affected since it goes straight to the rear lights. Plugged it into the bus and blew 2 fuses in the TOAD wiring control board in the bus ... drat. Thank you for isolation relays. Well at least we had the right blinker. Deb was right, we should have spent some time with this and just left late ... oh well.
Short story:
The MFSW and flasher relay failed and shorted to ground. I am not sure which device failed first but the pair took out the brake light fuse and the MFSW fuse and subsequently two of the TOAD control board fuses.
Long Story:
Determined that fuse 2 for brakes and fuse 27 for the MFSW were blown. Fuse 13 for the blinkers was OK. Replaced fuse 27 and it blew instantly. Replaced fuse 2 but still no brake lights.
With the flasher relay in place, there was 12 volts across the blown fuse 27. Without the relay in place this short went away. Great, new relays are easy ... darn, new relay did not solve the problem.
Since the jeep uses a combination blinker / brake light assembly, the rear brake light wiring goes through the flasher relay.
I removed the flasher relay, disconnected the wiring harnesses from the MFSW and the brake pedal switch and removed the tail lamps. Using an audible ohm meter I worked my way through all of the segments of wiring between the various devices to determine if any was shorted to ground. All of the wiring appeared to be ok.
Since I do not do this all the time, I did make one rookie mistake that cost me some time ha! I totally forgot about the normal incandescent lamp in the third brake light above the spare tire! Since this brake light is connected ahead of the flasher relay it looked like a short. When I made my way back to the tail gate wiring connections I realized this and with the third brake light lamp removed, the short was gone ... whew.
With all of the wiring checking out, I bought a new MFSW and flasher relay and installed them.
Still had 12 volts across fuse 27 making me think that it was not the switch, but that turned out to be because the new MFSW was shipped with the hazard lights engaged so it was connected to all of the exterior lamps. Turned off the hazards and all was good.
So, we have blinkers and brake lights and are no longer looking over our shoulder and using hand signals. Just shy of $90 for a mid grade MFSW and $30 for the relay. Deb bought me a whisky for my time.
According to the Jeep forums, the MFSW failure is pretty common for this vintage and presents itself in various ways. Apparently, several people have purchased faulty MFSW and had to get a second one. I am assuming / hoping that these are the cheap ones.
This must have happened on the way to the bus as the blinkers and brake lights were not working upon arrival. With no time to trouble shoot, I did not realize that we had two blown fuses and simply hoped that it was a relay or switch and that the jeep "trailer" wiring was not affected since it goes straight to the rear lights. Plugged it into the bus and blew 2 fuses in the TOAD wiring control board in the bus ... drat. Thank you for isolation relays. Well at least we had the right blinker. Deb was right, we should have spent some time with this and just left late ... oh well.
Short story:
The MFSW and flasher relay failed and shorted to ground. I am not sure which device failed first but the pair took out the brake light fuse and the MFSW fuse and subsequently two of the TOAD control board fuses.
Long Story:
Determined that fuse 2 for brakes and fuse 27 for the MFSW were blown. Fuse 13 for the blinkers was OK. Replaced fuse 27 and it blew instantly. Replaced fuse 2 but still no brake lights.
With the flasher relay in place, there was 12 volts across the blown fuse 27. Without the relay in place this short went away. Great, new relays are easy ... darn, new relay did not solve the problem.
Since the jeep uses a combination blinker / brake light assembly, the rear brake light wiring goes through the flasher relay.
I removed the flasher relay, disconnected the wiring harnesses from the MFSW and the brake pedal switch and removed the tail lamps. Using an audible ohm meter I worked my way through all of the segments of wiring between the various devices to determine if any was shorted to ground. All of the wiring appeared to be ok.
Since I do not do this all the time, I did make one rookie mistake that cost me some time ha! I totally forgot about the normal incandescent lamp in the third brake light above the spare tire! Since this brake light is connected ahead of the flasher relay it looked like a short. When I made my way back to the tail gate wiring connections I realized this and with the third brake light lamp removed, the short was gone ... whew.
With all of the wiring checking out, I bought a new MFSW and flasher relay and installed them.
Still had 12 volts across fuse 27 making me think that it was not the switch, but that turned out to be because the new MFSW was shipped with the hazard lights engaged so it was connected to all of the exterior lamps. Turned off the hazards and all was good.
So, we have blinkers and brake lights and are no longer looking over our shoulder and using hand signals. Just shy of $90 for a mid grade MFSW and $30 for the relay. Deb bought me a whisky for my time.
According to the Jeep forums, the MFSW failure is pretty common for this vintage and presents itself in various ways. Apparently, several people have purchased faulty MFSW and had to get a second one. I am assuming / hoping that these are the cheap ones.