[Silly Little Cars] Brake Lights Out

Tue Oct 13 16:07:35 PDT 2015

Mike,

The wording of your questions lead me to believe that you have very little experience servicing electrical circuits, so my response below is written about as simple as I can make it. I hope it helps you find the problem.

All fuses can be tested with a multi meter that is set to Ohms and the RX1 scale with the meter turned on. Remove the fuse and touch the leads one to each of the fuse contacts while holding the fuse in your hands. With both leads connected to the fuse the meter should read 9999 (infinity) before you touch the leads  and nearly 0.00 ohms when the leads are connected. If the meter stays at or near the 9.999 reading, the fuse is bad. If it reads anywhere near 0.00 ohms the fuse is good. Plug it back in and go to the next fuse, remove it and do the same test on it. You can test all of the fuses this same way in about 10 minutes. The one that doesn't read close to zero ohms (doesn't deflect the meter needle) is the bad one. Find or buy another
fuse of the same type and with the same ampere rating, test it just like you did the other fuses to be certain that it's good, and then install it. The multi meter should never be connected to a voltage source when it is set to any Ohms or Ampere scales. You will damage the meter if you do this. Always set the meter to the correct scale for the iintended test BEFORE connecting the leads. 

Fuses are designed to shut off the power to a circuit when an overload condition occurs. You will need to find and correct the reason that the fuse blew out before replacing the fuse. If you don't, the new fuse will blow out too. It's a good idea to keep a set of spare fuses in the vehicle to help keep you from getting stranded. Carrying a copy of the electrical diagram and a multi meter in the car is a good idea too.

You can buy a multi meter for as little as about $6 from Harbour Freight that will be sufficient for voltage and resistance tests, but don't expect it to last forever. You get what you pay for. Similar, but much better made, multi meters are available for as much as $300. They will last longer and be more accurate, but the Harbour Freight meter will be adequate for finding basic electrical problems in your Interceptor. Heck, at $6 you can buy a new one each time you have an electrical problem. I have several good quality multi meters for serious electrical work, but I also have about a dozen of these Harbor Freight meters scattered around where I might need them, one in each car, one in the boat, one in each tool box, etc.

You can do many other tests with your multi meter once you have a basic understanding of electrical circuits and how to use the meter to diagnose electrical problems. With the multi meter set to DC Volts and the meter turned on you can test your battery voltage by touching the leads of the meter to the battery terminals, one lead to each terminal, and you can also look to see if voltage is reaching your tail lights by connecting the black lead to the vehicle frame (bare metal) and the red lead to the wire connection (bare metal) at the tail light. When the light is supposed to be lit the meter should read about 12 volts DC. You can follow the wiring back toward the headlight/tailight switch checking each electrical connection point where the tail light wiring connects to see if voltage is present the same way, looking to see where there is voltage present and where it is not present.Working from the tail light to the headlight/tail light switch the problem will be between the first place that has voltage present and the last place that you tested where the voltage was not present. Looking carefully at the wiring between these two points should allow you to see the problem. It helps a whole lot to have a wiring diagram of the circuit that is malfunctioning, so you can see where all the places are that the wire connects. It's like a road map for the wires and it makes finding electrical problems much easier. 

Charley 

  ----- Original Message ----- 
  From: Mike Aisenfeld via Silly_little_cars 
  To: Silly Little Cars 
  Sent: Tuesday, October 13, 2015 3:14 PM
  Subject: [Silly Little Cars] Brake Lights Out

  Hey Everyone,

  This question isn't nearly as exciting as some of the recent posts, but it will be very helpful to fix.  I have a 99 Interceptor (Ford powertrain) and my brake lights went out a few weeks back.  I would usually check the fuse and then replace the switch if it wasn't a fuse.  I hit a wall with both of these simple tasks.  

  Rather than a standard fuse box, there seems to be a series of large square fuses along the engine compartment just behind the cab.  The previous owner painted over all of the fuses when the car was painted so I don't know which is which.  I also don't know how to test these types of fuses.  Any idea which one would control the brake lights or how to test them?
  I then thought I would just replace the brake switch, but you can't access the back of the master cylinder from the front when you remove the sheet metal panel and the dash is riveted together.  I can drill through the rivets, but I thought I would check in before I started taking things apart.  Any pointers here?

  Many thanks,

  Mike
  SF

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