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Triumph TR6 - When looking for a short......

What exactly am I looking for? I have a short in the circuit that runs the gas gauge, temp gauge, turn signals, heater fan and stop lights. This I know because the fuse has blown twice in the last week. I suspect the right rear tail light, because I disconnected the heater fan, which was my first suspect and that didn't solve it.

What do I do with my little voltmeter to fine it? I presume one of my little sockets or something that is positive is touching the frame or something that is grounded to the negative, and creating the illusive short circuit. But how do I figure out which one? I have a suspicion it is the right rear stop light because it wasn't working, or so my wife said, when I first started having the problem, but when I checked it with a new fuse, it was working. Anyway, can one of you wiser, although not necessarily older, guys tell me how to go about this little experiment.

Thanks, John. PS, it was in the high 70's today, going down to the low 60's or high 50's tonight. And I was afraid to drive the 6 because of the brake lights! Woe is me.
JL Bryan

First disc the positive battery terminal then remove the fuse for that circuit then using the x1 ohms scale on your meter ( when you touch the leads together the needle goes to zero or you may have a beep option instead ) touch one lead to the load side of the fuse holder and the other to the neg side of the battery and see if it ohms to zero or beeps.
If it does then you know for sure its on that line and now you just have to isolate one by one the lights, heater etc by the same way.
Charlie Ballard

What years your car?
Green circuit has lots of goodies.
If that light is out it could be/ bad bulb/ bad connector/bad ground.

If the fuse blows when installed ignition turned on. Its a definite ground problem. Dead short. That as you say doesn't happen?
If it goes after a bit there is either too much load or intermittent ground. Could still be heater fan? Only thing you have run lately thats unusual right. Poor fellow?

Have wife watch start car and turn on all devices brake turn signal and both together. Heater and then Brake and turn.

You can test current load with a standard home meter. Most are restricted to 10 amps. with a secondary place to connect for amps. You may blow the meter. Fluke makes a good clip on for automotive bout $400 Can.

You have to open the circuit. Voltage can be tested to ground amps can't. The meter has to be placed in circuit. For the bulb as example you remove the connector and connect one wire of meter to the disconnected wire and one to the bulb connector all set in amp mode on meter. Then turn circuit on. I won't do the math here may make a mistake! But your looking for the wattage of the lamp converted to amps at 12 volts compared to the draw registered on the meter.

Bill Brayford

Thanks, guys. It is a 71 and I have the Bentley manual and the wiring diagram, and I know how to read the diagram as I spent part of my youth messing with ham radios and electronics. I will try the meter this weekend and see if I can isolate the problem. When I got the car last year, with the gracious help of Jim, Dan Masters and others here, I went through all the electric connections under the hood, cleaned them and used dialectric grease on them. I vaguely recall taking the left rear lights apart, but I think I ignored the right one because everything seemed to be working okay after that. More recently, I disconnected the lead to the fan motor (under the dash end) and still had the problem, so it probably isn't there. I guess I'll be taking the right rear tail light assembly apart this weekend, but after I do as you guys suggest. Thanks, John.
JL Bryan

This thread was discussed on 04/02/2004

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