My volt meter normally sits happily at about 13.5V.........but on a 4 hour trip the other day, it suddenly shot to 16 volts. I thought perhaps it was the heat, but when I started the car from cold yesterday, the meter went straight to 16 volts again. Any ideas as to where to start on this, or am I going to have to cough-up for a new alternator?
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It was James Bond's colour... Saffron Yellow is so cool :-) -
David, firstly check the voltage at the battery terminals with the engine running, also the voltage at the incoming and outgoing side of the voltage regulator. Any other instruments reading abnormally?
steve. -
Hi Steve. You always learn something new when doing a job on the Stag......I had no idea where my voltage regulator was! But I'm wondering if I have caused the problem myself, as I havediscovered that the regulator is behind the Speedometer. Before the 4 hour trip I mentioned in my post, I had just reconnected the speedo cable. However on inspection everything is connected up as it should be......so I am none the wiser :-(
So with the car running, the readings are:
Battery 14.3v
LH connector of the regulator, a steady 13.9v
RH connector of the regulator varies wildly from 2.9v to 11.4v
The two middle connectors of the regulator have no wires attached, but they both varied in volts too.
Does this mean anything to you?It was James Bond's colour... Saffron Yellow is so cool :-)Comment
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Strongly indicative of a failed V regulator. If you've got a multimeter, you can check the voltage at the battery to confirm this has not got to the 16V seen on the gauge (will probably be 14 - 14.5V with the engine running at 1,500 - 2,000rpm).
The fuel gauge is the only other instrument fed from the V regulator, this would be reading higher as well.
The V regulator works by switching the battery voltage on and off, with the time intervals designed to provide an average of 10V output to the 2 instruments. Failure to regulate the average voltage is usually either a failure within the regulator (readily available at ~£15), or it could be that the earth to the regulator is defective - best place to first look. It's mounted on the rear of either the tacho or speedo. The dark green wire is battery volts fed from Ignition Control fuse. The light green wires go to the Temp and Fuel gauges. I think the earth is achieved by connection between its can and the speedo/ tacho it's bolted to (which will have a black wire connected).
Suggest you remove the Ignition Control fuse whilst checking connections.
Jonno
White 1976 build ("Mk2") only a few modsComment
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Could be the black wire to the speedo became detached whilst refitting the speedo cable.Originally posted by DavidW View Post
White 1976 build ("Mk2") only a few modsComment
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Agreed, sounds like voltage regulator failure. Not serious if only that.Comment
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Hi StagJonno. No black wire to the Speedo at all (I'm a Mk 1 if that helps). The only wires I have are to the illumination light. The wires to the Volt Regulator are a dark green and a light green...............I do have a black earthing wire on the rev counter though?
It does look like the regulator is at fault being as I now know I'm not getting 16v to the battery........Phew! :-)
Thanks guys :-)It was James Bond's colour... Saffron Yellow is so cool :-)Comment
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There has to be a black wire to the speedo for both the V regular and instrument illumination to work. It may have fallen off and be hiding in the void.
JonnoWhite 1976 build ("Mk2") only a few modsComment
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Voltage regulator only supplies temp and fuel gauges (light green wires). The output from the VR should be a mean of 10v. You might get a reasonable indication using an analogue voltage tester, but not a digital one.Dave
1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.Comment
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Ill have a look into the void (sounds a bit Star Trek) - thanks Jonno :-)It was James Bond's colour... Saffron Yellow is so cool :-)Comment
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