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brakes
- Thread starter deess
- Start date
dabtl
Active member
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- Location
- Denton, Texas
Check the grounding of the tail lights first. Then start looking for shorts if the brake light switch is working.
Barrman
Well-known member
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- Giddings, Texas
The top lever on the 3 lever switch has to be either one or two clicks to the right for the service brake lights to work.
If you did that and still no brakes. You get to start tracing the wiring.
Crawl under the truck and use a 5/8" wrench to remove the 2 bolts on skid plate under the brake airpack. Either at the very front of the air pack or between the air pack and the frame there will be a big rubber plug with two wires on it. The metal tags on the wires will be 75 and 75A.
Pull the plug off the air pack. With the 3 lever switch set properly, you should have power at one of the wires on the plug. Use a test light to check. No power on either wire means you either have a bad wire or a bad 3 lever. Try it in the headlight position and in the b/o light position since the b/o brake lights are powered from the same switch. If it works in one, but not the others then it is the 3 lever switch.
However, if you get power to the plug your switch is probably ok. Next you need to stick a jumper wire across the plug. Just put a wire in both connectors on the plug. It will spark when you connect them if you still have the 3 lever in a brake postion. You should have brake lights now. If yes to the brake lights, then your switch on the airpack is bad.
If no to brake lights. Then you get to search some more. With the jumper still in place, try one of the bulb sockets at the back. If still no power, start tracing the wiring back to the front of the truck. Wire #22/460 or 22/461 will be your brake lights. Check every plug and especially the big connector on the inside of the frame rail beside the air pack.
If you still find nothing and have nothing. We are back to the 3 lever switch again and just for fun, the 7 pin blinker arm wiring harness. At this point, you need to print out a wiring diagram, unplug the 3 lever and the blinker arm and verify that every wire on there actually goes to where it is supposed to. If they all do, then the 3 lever is your problem.
If you did that and still no brakes. You get to start tracing the wiring.
Crawl under the truck and use a 5/8" wrench to remove the 2 bolts on skid plate under the brake airpack. Either at the very front of the air pack or between the air pack and the frame there will be a big rubber plug with two wires on it. The metal tags on the wires will be 75 and 75A.
Pull the plug off the air pack. With the 3 lever switch set properly, you should have power at one of the wires on the plug. Use a test light to check. No power on either wire means you either have a bad wire or a bad 3 lever. Try it in the headlight position and in the b/o light position since the b/o brake lights are powered from the same switch. If it works in one, but not the others then it is the 3 lever switch.
However, if you get power to the plug your switch is probably ok. Next you need to stick a jumper wire across the plug. Just put a wire in both connectors on the plug. It will spark when you connect them if you still have the 3 lever in a brake postion. You should have brake lights now. If yes to the brake lights, then your switch on the airpack is bad.
If no to brake lights. Then you get to search some more. With the jumper still in place, try one of the bulb sockets at the back. If still no power, start tracing the wiring back to the front of the truck. Wire #22/460 or 22/461 will be your brake lights. Check every plug and especially the big connector on the inside of the frame rail beside the air pack.
If you still find nothing and have nothing. We are back to the 3 lever switch again and just for fun, the 7 pin blinker arm wiring harness. At this point, you need to print out a wiring diagram, unplug the 3 lever and the blinker arm and verify that every wire on there actually goes to where it is supposed to. If they all do, then the 3 lever is your problem.