Join Date: Mar 2002
Location: Austin, TX, USA
Re: Brighter Tail Lights Needed
I agree with Kevin - try the simple things first.
Use the voltage drop method of verifying the connections. Theoretically measurements between two power points or two ground points would show 0.00V. In reality, some small voltage drop will exist (less than 0.05V give or take), but larger voltage drops indicate a problem. Here is how it's done.
Get a digital volt meter and a length of wire. An electrical extension cord will work in a pinch. A jumper cable works also. I have a 10' length of 12ga copper wire with aligator clips on each end that I use. Some engineering may be required to make the connection if you don't have alligator clips or a jumper cable. Just be safe and don't allow the battery (+) to touch ground.
Connect the wire to the battery (+) connection. Connect the other end of the wire to one lead of your volt meter. Connect the other volt meter probe to the power wire of the lamp your testing. Activate the tail lamps (all these tests require activating the circuit to measure the voltage drops) and read the meter voltage. You should see a very small reading (less than 0.05V). If you see more than that you have a bad connection somewhere.
If you discover you're loosing voltage in the power circuit, repeat the test at other places in the circuit. For example, measure between the battery (+) and the brake light switch, or marker lamp switch to isolate the front portion of the harness. You can also measure, for example, between the lamp power wire in the rear and the lamp switch to isolate the rear portion of the harness. A switch can be checked by meausring the voltage drop accross the switch itself - bad connections will show voltage on the meter and good connections will show nearly zero volts.
Beware that some of the rear lamp circuits interconnect with the turn signal switch in the steering column, so be sure to isloate / check voltage drops there as well. Just remember the readings only have value when the circuit is powered up and functioning (or attempting to function). This may mean you need a helper to push the brake pedal when checking the brake lamps.
And finally, (and just as important) the grounds can be verified by the same method by measuring between the battery (-) and the lamp ground in the trunk. Checking between the battery (-) and the fender is a good way to verify the body ground pig-tail. Again, look for small readings for a good ground - higher readings indicate a bad connection. When verifying a ground connection point, be sure to check the terminal end, screw and body separately. Lots of bad connections exist at those connection points where rust and oxidation accumulate between the screw and terminal end.
Once you're sure you don't have any major electrical system problems, and if you're still not happy with the lamp brightness, move on to the upgrades. Just about every 1st gen on the road has lots of sub-par connections that need a little sandpaper and dielectric grease to restore them to original working order.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI