MGB Register Forum

hi, just acquired a volt meter. Can anyone advise me how to connect it.
Many thanks in advance
Mario

Hi Mario
Looking at your list of cars your MGBs are all Negative earth with an alternator. A voltmeter simply connects between a convenient place across any live feed to the earth (car body). I think I would be tempted to wire it between the Brown wire at the fuse box to the terminal marked positive (with either +ve or simply + ) on the back of the voltmeter using a brown (or red) wire , and the negative terminal ( -ve or simply -) on the back of the voltmeter to a convenient body earth point using a black wire. The voltmeter should then read 13V -ve when the ignition is turned on. It will drop to around 12V when cranking and then show 13V with the engine running. If it doesn't read or tries to kick to the left on the dial then reverse the connection on the back of the voltmeter.
Voltmeters are only sensing instruments and don't have high currents passing through them so the job of wiring them up is straightforward. The reading they give shows the condition of the battery. Around 13V is normal for a battery in good condition, below 12V it is likely to need changing soon.

I have to disagree with Pete. The meter should be connected to the connection on the ignition switch which becomes live when the ignition is switched on (not the auxiliary position. Connecting to the nearest ignition controlled source or fuse results in low readings because of voltage drop. The voltmeter on my. Land Rover is connected to an ignition controlled fuse and it reads just about 13 volts but 13.8 volts is the reading across the battery on a fast tickover.
Connecting it straight to the switch avoids voltage drops. I'll be reconnecting the meter to the switch.

Bearing in mind my previous acknowledgement that autoelectrics are not my strongest suite, I can say that I use a simple digital voltmeter which plugs into my MGB cigarette lighter socket. Live when the ignition is switched on of course. That could be the simplest location on the dash to make a connection perhaps? Reads around 12.5 - 13v when switched on, and then around 13.5v with the engine running.

No holes in the dashboard required and it gets unplugged and placed in the glovebox when not needed.

Ian F

Hi Mario,
Ignore my advice. Vic's method of connection is far better. If you do it the way I suggested, the voltmeter will read all the time, even with the ignition off (unless you have an electrics isolation switch). So not a good idea!
Also I think the voltmeter will draw a small amount of current so would flatten the battery over time if you do as I suggested.
Sorry for the confusion,
Pete

hi all,

Many thanks for your advice. As usual really find them helpful

regards

Mario