I’ve discovered that the wire feeding the ‘B’ terminal of the stabilizer has no power comeing from it, it is a two wire one with a spade terminal and looks to be a faded light green. It goes down into the harness
This explains why none of the gauges are working, I changed the stabilizer before I realised there was no power.
I can’t see that wire on the +2 diagrams that I’ve got.
Any ideas please, Thanks very much John
John,
The Elan had a pretty consistent wiring scheme throughout its life, for whatever reason the +2 did not. On the Elan, green is the general purpose switched supply, fed from the ignition switch via one of the two fuses. To get to the voltage stabiliser, it meanders around behind the dash and goes via a number of connectors - any of which could be at fault.
If you can give me the model / year of your car, I will see if I can find a wiring diagram to suit and have a look. It would be helpful to know how many fuses you have.
If you have a link to a wiring diagram you think actually applies to your car, that would be very helpful.
Andy.
Andy
It’s a 1971 S130 three fuse box model, the diagram that I have is the one in the Lotus workshop manual ‘+2 S with alternator’ not exactly for a S130. The colours shown of the wires needless to say are not all the same as mine. The double one going to the ‘B’ on the stabilizer I’m sure is original because it is virtually grey in colour.
Thanks for trying to help. John
John,
I had a quick look at a 3 fusebox +2 diagram. It would suggest power to the stabiliser is white (the B connection), and the feed from the stabiliser to the instruments is light green (the I connection), but as I mentioned, the +2 is known to be inconsistent.
Typically, the connections on the stabiliser are a mix of male and female. The B terminal on the stabiliser is male, and the I terminal female - I guess to avoid problems during construction. Is this how yours is arranged?
Has the wiring been messed about by a PO, or is it all original behind the dash, and have the gauges ever worked?
Andy.
I have fitted a Clocks4classics tacho conversion to suit my electronic dizzy, it works fine very pleased with it, just needed to join the two bullet connectors together from the old tacho internals.
The engine will run without any tacho fitted but I had some of the connections come off the stabilizer but I’m sure they are reconnected correctly
All the gauges have always worked up until now and I’ve checked all the fuses still need to find some power for the
‘B’ terminal
John
John, I’ve been working on a plus 2 130s recently
Light green is the feed to the gauges (water temp and fuel) this takes its 10v from the voltage stabilizer so if it’s unplugged then it won’t read anything.
Not sure on the actual stabilizer contacts as I’ve done away with the original one and fitted a modern solid state unit
John,
Thanks for the info. Clearly something is adrift.
The wiring diagram and pptom’s post indicate the green wire you have is the feed to the other instruments, and not the supply, which should be a white wire - but given it is a Lotus, anything could be going on.
What colour wires do you have connected to the stabiliser and to what connections?
Andy.
Hi checkrail,
The voltage regulator on these cars does not actually regulate the voltage at all.
It is simply a bi-metal thermal make and break contacts set up, a bit like the points in the dizzy.
Positive 12V (+DC) current is intermittently fed to the Fuel and temp gauges, rather than a continuous current.
The actual voltage supplied to the gauges is always 12V never the 10V, or to be more accurate, the stabilizer only outputs the same voltage that is put in to it, ( o/put V = input V ). Therefore this is not a voltage stabilizer at all in the way a ‘solid state’ voltage regulator is.
Please note there is a difference in terms, stabilizer and regulator.
These stabilizers can sometimes be fixed but you will need to open up the device by bending the casing dents open so that the assembly platform can be withdrawn. If you get that far you will be able to see the simple contact points mechanism. These devices fail at the winding on the primary electrode or the contact points.
The contact points can be cleaned up but if the winding has gone open circuit you will need fairly high skill to fix it.
The green wires go to the gauges, the black to earth, and whatever colour you have on the third wire or wires is the 12V DC supply. The default condition of the stabilizer is there should be electrical continuity across the supply terminal and earth terminal via the internal contact points. If you have continuity here, you can probably fix the device but you will have to open it up to do so.
If you ever have a +12V reading from the two green wires, you have a problem.
Regards
Satyr Icon
Satyr is quite correct for the original Smiths stabilser, but all the modern replacement units now available have a semiconductor voltage regulator in them and do actually output 10v.
Of historic interest, the semiconductor used in these modern regulators is usually a ‘LM7810’ which is probably the oldest semiconductor design still in production and dates back to the late 60s - and is therefore period correct for the Elan.
£1.69 will buy a pack of 10 LM7810 regulators (plus postage) on eBay if you fancy having a go at converting your old stabiliser.
Thanks for the info. I have finally got the instuments back working, the battery gauge has it’s own feed connection,
Also have ordered a Wynd replacement unit
Cheers John
I always wondered why 10V?
The target voltage needed to be something below the lowest battery voltage likely with the auxiliaries on, and the engine off - with a bit of extra headroom. No good having the fuel gauge change if you turned the headlights on before you start the car.
I would imagine the stabilser and gauge system was a nightmare to design, mechanical systems are a pain at the best of times, everything is non-linear and manufacturing tolerances a mile wide. It may be that the on/off effect of the heater and bimetallic strip was only effective over a narrow range of voltage drop, or the gauges were problematic with voltage levels too low. The low chopping frequency would also be an issue, if (say) 5V was the target voltage, you may notice the gauges swinging backward and forward given the narrow mark/space ratio required to drop the effective voltage this far.
Finally, you should never underestimate the attraction of a round number, I have seen many designs where the main justification of choices made seem to have been based on exactly that.
It should be more technically named a power regulator but that would cause even more confusion.
Energy / Time. It regulates the Time as the load increases, 1. 2. 3. Gauges or input voltage changes.
The heating element wrapped around the bimetallic strip is connected between earth and the switched output. As such, the frequency and mark / space ratio of the output depends entirely on input voltage, and not on the number of gauges connected.
Andy.
Hello All,
Never thought there would be this much interest in the workings of the ‘‘voltage regulator’’.
This volt/reg is actually a device very similar to an indicator flasher unit and operates on the exact same principle.
The only notable difference is the on/off or ‘‘chop frequency’’ is accurately matched to the mechanical INPUT RESPONSE of the fuel and temp gauges.
The VR only SIMULATES a +10V current and the gauges are only designed to respond accurately to this SIMULATED output. They are NOT designed to respond properly to a true ‘continuous’ +10V.
A semiconductor device will deliver a near as damn it continuous +10V but the dials will show a higher temp/fuel level than the correct level. 
Maybe lower.
Please excuse the hijack here but since there seems to be some ‘electronics’ guys on this site, does anybody know the correct ‘‘mike’’ of the electrolytic cap on the PCB of the rev counter in a 1973 +2.
I replaced mine some time ago with he closest match I had but struggled to get a 3,000 rpm reading at 100Hz.
The original cap was illegible but looked like .4 mike.???
Satyr.
That’s very interesting- I owned a 1986 Turbo Esprit from 2010-14 and had two friends in my local area who had '87 Turbos. I’d met them before I bought mine, long story there, but before I bought mine I’d helped one of these chaps sort some issues with his car. One that we didn’t solve was that the fuel and temperature gauges would slowly oscillate together over an excursion of about 25% of their ranges. Too slowly to see it happen in real time, but glance every few minutes at the gauges and you’d see the changes. The Turbo Esprit also used these stabilisers, and he changed the thing three times thinking he kept getting bad replacements but the oscillation never went away.
Fast forward a few years. My Turbo had the same oscillation of the same two gauges and since we hadn’t cured it in my friend’s car, I just shrugged it off as a charming quirk of a British electrical system since it didn’t do any harm. Then one day I was doing an oil-change, which due to the location and orientation of the oil filter on the 9XX engines is often a messy job. I was wiping spilled oil off the side of the block when I noticed that two of the three bolts on one of the engine-mounts were visibly loose, enough to have backed themselves out a bit. One of them also secured the earth-strap to the engine. I cinched them up tight and though nothing about it, but then the next time I drove the car I noticed that that oscillation of the gauges was gone for good. Why the engine’s earth was the deciding factor in that I’ve never quite been able to work out, but then I’m no electrical engineer.
Oh yes. And I’ve read of a museum in Germany that opens at an odd time and charges an odd admission just to mess with the particularly Germanic obsession with nice even round numbers.