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Brake light fuse keeps blowing in my 1997 Suburban only when towing trailers.

The brake light fuse on my 1997 Suburban K1500 keeps blowing ONLY when connected to a trailer. If it's connected to a 4-pin trailer the fuse blows immediately. If to a 6 or 7-pin connector it blows at some later point. It never blows when not connected to a trailer and I've tried several different trailers, ruling out the trailer as the cause, and pointing toward the Suburban. What is the cause of this? Sometimes it's immediate, sometimes it lasts for several hours. I can't locate any chafing or exposed wires anywhere on or near the wiring harness or up to the tail lights themselves. Would a poor ground possibly be the problem?

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Barry Webster

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  • 35 Answers

If the fuse blows on different trailers then it's all down to the vehicle. You either have incorrect wiring on the vehicle, a short OR the fuse is not of a high enough value to cope with the additional brake lights? You could try removing all the trailer bulbs EXCEPT the brake lights - e.g. if it's trying to power up the indicators too? That would stop the fuse blowing...... OR remove the brake bulbs from the vehicle & see if it operates the trailer without blowing...... Check the total wattage of ALL the brake lamps & see if the fuse is actually of a high enough rating? Be aware though that increasing the value of the fuse could cause damage elsewhere! As a rough guide a 25 watt bulb will pull around 2 amps at 12 volts - so 4 bulbs may pull up to 8 amps & clearly blow a 5 amp fuse! If in doubt take it to an auto electrician...... The wiring needs to be correctly protected!

Posted on Apr 02, 2017

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pops296

Mike Tillman

  • 174 Answers

SOURCE: Trailer brakes

Take a 12 volt test light... the kind that has a spring loaded clip to hold the probe into the wire, and insert it into the wire just before the trailer plug, vehicle side. (Blue I think) If there is a connection, the brake should see it and you should have an indicator light. When you activate the brake the test light should lite up. If not, move up to the brake actuator and test the blue wire. If there is nothing at the actuator, check the black wire. It is power to the controller. If no power there, check fuses again. If it does pick it up at the plug, connect the trailer and test the trailer itself. First ground to the trailer and then to the truck. Most problems are ground wire related. Then move to the axle and test it there. For the brakes to work, and even show on the indicator, there has to be a ground and power to the brakes themselves. There are 2 wires to each brake... a ground and a power. Test across both wires to make sure you have power and ground. You can also hook another trailer to your truck or another truck to your trailer. Lights can work through trailer ball ground. Brakes can't. leave the trailer unhooked from the trailer and hook the wiring up and test the lights. That usually will indicate a good or faulty ground. Also make sure there is a GOOD ground to the truck frame/body. Also try http://www.etrailer.com/faq-wiring.aspx. They have a great website with lots of info. Hope this helps. Mike

Posted on Oct 07, 2009

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ftw1952

frank thomas wilson

  • 10319 Answers

SOURCE: tail light wiring connectors and wiring diagram

A test light checking each connector would be faster and easier to do. Maybe somebody may have a illustration for you but by far a simple test light is all you need with a helper turning on the different lights as you check them out and writing all your findings down

Posted on Jan 22, 2010

ftw1952

frank thomas wilson

  • 10319 Answers

SOURCE: how to connect a 4 wire trailer system to a 1994

Tail lights and brake lights are on the same wire.
Connect the wire from the brake light to the connector in the car to the tail lamp wire connector and you will be set to roll

Posted on Apr 04, 2010

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