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MG MGB Technical - gauges

I have 1976 MGB. I have a problem with my fuel and temp gauge, looking at the fuel gauges from the back were the green and black cable are suppose to be connected? The temps gauge the green and blue cable where does this go to? Also the gauge volt stabilizer is getting hot and the green cable is blowing fuses do you think the stabilizer could be bad oor cables are connected backward?
jorge

I've already sent the following to Jorge but repeat it here in case it helps others:

"First and foremost it doesn't matter which way round the gauges are connected, but it *is* important that neither wire is grounded except via the relevant sender in the tank or head. The sender itself does have to be grounded through its mounting tab, or the gauges will read high.

"With blowing fuses it does sound as if something is grounding somewhere. If it were either the green/black (fuel) or green/blue (temp) wires then the relevant gauge would be reading off the scale, but that wouldn't be enough to blow the fuse. If one of the gauges were grounding internally then that
could cause the problem, so disconnecting the light-green/green wire first from one then the other (and reconnecting the first) should show which gauge is causing the problem, as the good gauge should read normally when connected on its own.

"But if the stabiliser is getting hot then possibly it is shorting out internally, in which case it will still happen with the light-green/green wire disconnected from the sender and only the green connected.

"If it is the stabiliser then disconnecting the green from the sender as well will stop the fuse blowing (but of course the gauges won't work).

"However the stabiliser does get warm in use, so what you are feeling could be normal and the fuse is blowing because of a short on the green wire elsewhere, which will stop the gauges working as well. But at the risk of confusing things even more, that should also stop the stabiliser getting warm. So because it *is* getting warm, I suspect it is a short on the light-green/green somewhere or a faulty gauge or stabiliser, and if you work carefully though the steps above you should be able to determine which. If you have an old headlamp bulb solder a couple of wires to one of the contact pads on the base and the metal can of the bulb, and connect that in place of the 2nd fuse up (which I assume is the one that is blowing). This will save you having to keep replacing fuses while you are testing, and if the bulb glows brightly you will know the short is on, and when it glows dimly or not at all you know you have disconnected the faulty component."

One thing to add is that the stabiliser *does* have to be connected round the right way to work properly, although having it round the wrong way won't blow fuses as is happening in this case. The spades on the wires and stabiliser should be one male and one female in each case to prevent reverse connection.

Paul Hunt 2

Paul,

Slightly off-topic but still to do with the voltage stabilizer: is the unit "directional" in that there is stamped on the case "top"? Does it really matter which way the stabilizer is mounted?

Just curious.

Cheers
Simon
Simon Austin

Thank you Mr. Paul, I founded the problem the bracket hold the fuel gauge was touching the gauge I making the extra ground point.
Jorge

Simon - yes it does matter, I'm not sure whether it is marked 'TOP' or not without checking but it should be suspended directly from its fixing tab and not tilted one way or the other. I've not had one open, but unless it has a heavy contact on the moving arm of the bi-metallic switch I can't see that a different orientation will have much effect. Although thinking further it could be that if the heated arm is vertical it could bend more from the effect of heat rising from the lower turns past the upper turns, than it it were horizontal.
Paul Hunt 2

This thread was discussed between 22/10/2007 and 03/11/2007

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