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The license plate lamps on my 67 MGB are shorting. There is only one wire to each fixture (the hot wire) and no ground wires were provided. From what I have been able to ascertain, the grounding is through the bumper to the chassis. Well, this gounding is apparently not very effective. Would running a small wire from the bulb holder to the lens screws help? I have tried taking the entire assembly apart but it didn't help.
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MGB Poor grounding license plate lamps 67 MGB
- Thread starter Rays
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RickB
Yoda
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Re: Shorting license plate lamps 67 MGB
Can you get the bulbs to light at all?
I mean, if you touch the ground side of the socket to a sure ground source do the bulbs light?
Not sure, but in my 70 the key has to be on for the plate lights to come on - is this so on the earlier cars?
Can you get the bulbs to light at all?
I mean, if you touch the ground side of the socket to a sure ground source do the bulbs light?
Not sure, but in my 70 the key has to be on for the plate lights to come on - is this so on the earlier cars?
Re: Shorting license plate lamps 67 MGB
Yes I can get the both lights to light by tapping on them and/or pushing on the bumper bar.
I isolated the short, it is not between the light bulb holder and the light fixture, nor between the light fixture and the bumper overrider but rather between the rear bumper overrider (which the license plate lamps attach to) and the rear bumper itself. I don't know why there wouldn't be a good earth between the bumper overrider and the bumper as they are attached directly to one another by a large bolt and nut.
There is a rubber gasket between at the joint of the overrider and the rear bumper bar, perhaps this prevents an adequate earth.
Yes I can get the both lights to light by tapping on them and/or pushing on the bumper bar.
I isolated the short, it is not between the light bulb holder and the light fixture, nor between the light fixture and the bumper overrider but rather between the rear bumper overrider (which the license plate lamps attach to) and the rear bumper itself. I don't know why there wouldn't be a good earth between the bumper overrider and the bumper as they are attached directly to one another by a large bolt and nut.
There is a rubber gasket between at the joint of the overrider and the rear bumper bar, perhaps this prevents an adequate earth.
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Re: Shorting license plate lamps 67 MGB
Ground would be achieved thru the bolt. R&R and clean that. Then get some paint on it.
BTW: A "short" implies a current running to ground. It produces smoke an' sparks. What you describe is an open circuit, discontinuity. Two different things.
The thread title was a bit misleading is all. /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
Ground would be achieved thru the bolt. R&R and clean that. Then get some paint on it.
BTW: A "short" implies a current running to ground. It produces smoke an' sparks. What you describe is an open circuit, discontinuity. Two different things.
The thread title was a bit misleading is all. /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif
tony barnhill
Great Pumpkin - R.I.P
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Re: Shorting license plate lamps 67 MGB
Should be ground wire! It should be black & should be in the wiring loom somewhere around the trunk locking mechanism
Should be ground wire! It should be black & should be in the wiring loom somewhere around the trunk locking mechanism
Re: Shorting license plate lamps 67 MGB
Thanks for the lesson! I'm still in the early learning phase of the MGB, including it's electrics. I am changing the title to more accurately reflect the problem at hand. /bcforum/images/%%GRAEMLIN_URL%%/blush.gif
BTW, the bolt that attaches the bumper overrider to the bumper bar is already very clean, as is its nut. The bumpers are relatively new as well, there is no dirt, rust or grime on any of the connections.
There is a ground wire attached next to the truck lock in the boot, it comes from the wiring loom. There still is only one wire that goes to each license plate lamp.
DrEntropy said:
Thanks for the lesson! I'm still in the early learning phase of the MGB, including it's electrics. I am changing the title to more accurately reflect the problem at hand. /bcforum/images/%%GRAEMLIN_URL%%/blush.gif
BTW, the bolt that attaches the bumper overrider to the bumper bar is already very clean, as is its nut. The bumpers are relatively new as well, there is no dirt, rust or grime on any of the connections.
There is a ground wire attached next to the truck lock in the boot, it comes from the wiring loom. There still is only one wire that goes to each license plate lamp.
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Re: Shorting license plate lamps 67 MGB
Yup. Th' red ones. Colin's ground strap fix has merit. If you run a properly lugged (solder'd or properly crimped lugs of appropriate size) wire from a chassis point to the nut/bolt of the over-riders it should be sorted. You said if you "rap" the bumperette smartly the light comes on?? It may actually be a problem in the sockets. Clean the contacts of both sides of the socket with some #600 grit "wet-or-dry" sandpaper. Skin a popcicle stick thin and narrow with a grinding wheel to use as a "tool" to fold the paper over for the insertion into the sockets.
Yup. Th' red ones. Colin's ground strap fix has merit. If you run a properly lugged (solder'd or properly crimped lugs of appropriate size) wire from a chassis point to the nut/bolt of the over-riders it should be sorted. You said if you "rap" the bumperette smartly the light comes on?? It may actually be a problem in the sockets. Clean the contacts of both sides of the socket with some #600 grit "wet-or-dry" sandpaper. Skin a popcicle stick thin and narrow with a grinding wheel to use as a "tool" to fold the paper over for the insertion into the sockets.
WA1KWA
Jedi Trainee
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Re: Shorting license plate lamps 67 MGB
Rays - Do you have a DMM (Digital Multi Meter)? Probably the best single investment for diagnosing electrical problems you can make. $30.00 - $40.00 at Sears or Radio Shack or Home Despot or wherever. There are ones that cost more but for most of us, the meters in this price range are more than adequate. Will save you from endlessly chasing your tail on electrical diagnosis. In this case, you could do a simple continuity test to see if the lamp has a connection to ground, if you are getting power to the bulb, if the bulb itself has continuity. This is a tool you will use far beyond your MG for years to come.
Colin
Rays - Do you have a DMM (Digital Multi Meter)? Probably the best single investment for diagnosing electrical problems you can make. $30.00 - $40.00 at Sears or Radio Shack or Home Despot or wherever. There are ones that cost more but for most of us, the meters in this price range are more than adequate. Will save you from endlessly chasing your tail on electrical diagnosis. In this case, you could do a simple continuity test to see if the lamp has a connection to ground, if you are getting power to the bulb, if the bulb itself has continuity. This is a tool you will use far beyond your MG for years to come.
Colin
RickB
Yoda
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Re: Shorting license plate lamps 67 MGB
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif
I've got a Fluke 77 which I've had for about 20 years.
It cost more, but it sure has served me well.
I just bought a new DMM - a cheap one (about $30) that does all the normal stuff (ohms, volts AD/DC, Amps) but has the additional features of doing Dwell & Tach. Kind of nice to have, not need to have - but nice.
Here's one:
https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4520036742
/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif /bcforum/images/%%GRAEMLIN_URL%%/iagree.gif
I've got a Fluke 77 which I've had for about 20 years.
It cost more, but it sure has served me well.
I just bought a new DMM - a cheap one (about $30) that does all the normal stuff (ohms, volts AD/DC, Amps) but has the additional features of doing Dwell & Tach. Kind of nice to have, not need to have - but nice.
Here's one:
https://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4520036742
RickB
Yoda
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Re: Shorting license plate lamps 67 MGB
Cool - the one I got like the ebay unit above has temp & diode & all that too. Here's another:
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200194062171
Cool - the one I got like the ebay unit above has temp & diode & all that too. Here's another:
https://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=200194062171