How do you find a short?

[dtharp113]

LSMS - right turn signal has been blowing fuse when you turn on RUNNING LIGHTS

No trouble when the unit is mounted into the body w/out the screws - inning lights come on and no trouble w fuse. When you add the screws, the fuse blows

Was suggested that "Check to see if hot side of assembly is shorted to the body of the lamp. That would explain why everything's OK when assembly is floating but shorts out when attached to the car body."

So my question is - which is the hot side and how do i tell if it's shorting to the body of the lamp?

[pkbinplano]

brown wire is always the ground on these cars. Check for chafe where the wires go through the fender . Should be a grommet there . Start there

[dtharp113]

Yup - grommet and rubber sleeve in place. No visible sign of chafing or breaks in the insulation

[02for2]

Both sides are 'hot'... there are two circuits with a common ground - it's a two filament bulb - 1 for running lights and one for turn indicator. The common ground is through the mounting screws to the body.

Make sure that there is no contact between the two wires, or terminals. Make sure there isn't corrosion or conducting debris in the bulb socket which could cause the short.

Absent any of this, you're just going to have to trace/inspect both wires for cracks, pinches, etc.

Cheers!

[dtharp113]

Thanks - I'm going to eliminate the turn signal first, then onto the wiring. Maybe I'll just look for plastic screws!

[pkbinplano]

check your rear right turn signal assy. Same, look for chafes in the wires running to it. Take trunk boards out and look under there

, open the light up and look around also

[dtharp113]

Really -- know the rear is on the same fuse, but you think that'll whack the front (assuming the front is in good shape)?

As you may deduce - I have no idea when it comes to electrical stuff

[BillWilliams]

You need metal screws for the ground.

[02for2]

You need metal screws for the ground.

Ditto!

If you use plastic screws, you will not complete the circuits at all, no short or anything else either... like lights that light.

Cheers!

[dtharp113]

No - As I originally said, the light works properly sans screws and int he body. It's only when I fasten it down w screws that the fuse blows

Hence - usings plastic screws

[BillWilliams]

It may not be the screws but when the screws put tension/pressure on something, pop goes the fuse.

Or your body has power all over it!

[jimk]

The screws complete the circuit for the light. Gotta have metal screws or light wont be gounded! Use a multitester with the screws out and test for voltage from the light to the fender/ground. Then remove the bulb and test for continuity from the center pin in the bulb socket to ground and locate the short.

[02for2]

This definitely points to one or the other supply (hot) wires shorting to ground somewhere, when you add the additional (correct) ground by screwing it to the body, it overloads the circuit and blows the fuse.

With a DMM:

•Remove the power feed (i.e. fuse, control module) from the suspect circuit.

•Disconnect the load.

•Set the rotary dial of the DMM to the ohm (Ω) position.

•Connect one lead of the meter to one end of the circuit to be tested.

•Connect the other lead of the meter to a good ground.

•If the DMM does NOT display infinite resistance (∞ or OL), there is a short to ground in the circuit.

Here is another helpful primer on using a DMM on all sorts of automotive diagnosis:

http://assets.fluke.com/appnotes/automotive/beatbook.pdf

Cheers!

[dtharp113]

This definitely points to one or the other supply (hot) wires shorting to ground somewhere, when you add the additional (correct) ground by screwing it to the body, it overloads the circuit and blows the fuse.

With a DMM:

•Remove the power feed (i.e. fuse, control module) from the suspect circuit.

•Disconnect the load.

•Set the rotary dial of the DMM to the ohm (Ω) position.

•Connect one lead of the meter to one end of the circuit to be tested.

•Connect the other lead of the meter to a good ground.

•If the DMM does NOT display infinite resistance (∞ or OL), there is a short to ground in the circuit.

Here is another helpful primer on using a DMM on all sorts of automotive diagnosis:

http://assets.fluke.com/appnotes/automotive/beatbook.pdf

Cheers!

Based on the instructions (and the results above) - I do have a short to ground as, when I hooked up my DMM, the readout was jumping all over the place.

Thanks for the step-by-step!

[aa/fd]

Now this is not supposed to be funny but I have seen it done "bypass the fuse and look for smoke" get a bigger hammer approach.

The guy I saw do this used a piece of copper tubing and placed it in the fuse block, yes he had smoke and fire, but he found the source and was pleased.

Unbelievable what so called "mechanics" will do some times. Last I heard he was still working on log trucks. Think about that next time you see one in you mirror.