License plate light problem on BJ8

[bighealeysource]

Hey all,
In my next life I think I will come back as an auto electrician tech so I don't have to ask so many questions
concerning Healey electrics ! That being said, my license
plate light works fine when testing it by simply connecting
to the battery but every time I hook it up to the harness
after re-installing on the back bumper, it immediately shorts
out my in-line fuse ( thank God for that advice ). I cannot
figure out what the problem is unless I have a bad ground but
why would that be with the harness grounded properly to the
chassis ( new harness BTW) and the light securely attached
with the mounting bolts . Any ideas out there ?
Thanks,
Mike

 

[TimK]

simply put, the hot lead must go through the bulb before it gets to ground. Something is shorting to ground without going through the bulb filament. You'll need to use a tester to make sure there is isolation from the hot lead to ground. Look for any path that may bypass the bulb. You can test for this by using an ohm meter to see if you have no resistance between the hot lead and the metal body of the light. You should have high resistance (open circuit)when connecting one lead of the tester to the hot connection and the other to the metal body of the light. Take the light apart and see where there may be a short.

 

[bighealeysource]

Hey Tim,
You were right on target. Went over the light again and sure enough, the red
and black wires had been connected backwards - red to ground and black to the
bulb ( have no idea how that happened,wink, wink). So, connected it correctly
and viola, we have light and no fuse blown !!! Thanks for your help, I had
looked at it so many times was simply missing the obvious.
Regards,
Mike

 

[TimK]

I'm really glad I could be of some help. It feels so good when you solve a problem like this. We all have done similar things.

 

[Michael Oritt]

"Went over the light again and sure enough, the red
and black wires had been connected backwards - red to ground and black to the bulb ( have no idea how that happened,wink, wink). So, connected it correctly and viola, we have light and no fuse blown !!!"
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Incandescent bulbs are not polarized and assuming the bulb receptacle is isolated from chassis ground it should not matter which way the wires are hooked up.

I suspect you had a grounding problem as was suggested--perhaps a screw or something was creating continuity some place between the power lead and ground--and while reversing the leads you fixed it.

In any case congrat's on having eliminated the problem.