+2 Spyder: Positive Earth?

[Bahtatboy]

I've just purchased a +2 Spyder (with a Zetec 2000cc), which was converted around 11 years ago (2010). I have the receipts for the build; included was a new loom. Very basic question: did Spyder always convert to negative earth, or not? I'm trying to wire up a HUD (Head Up Display): initially I just want to test that everything works ok, with power from the cigarette light socket, and then I intend to hard-wire it in. The existing cigaratte lighter socket is dead, so I've temporarily wired up a new one using power piggy-backed off the fuse box and earthed to a plate under the dash (which plate is used for other earth connections). I've tested the HUD / cable / cigarette lighter plug in another car, and all is fine; however, when I plug into the temporary socket in the Elan, the HUD won't start up. I've checked the voltage in the both sockets (that in the other car, and that in the Elan), and both have around 13V; the light comes on on the cigarette lighter plug, so the power is getting out, but isn't energising the HUD. I've double-checked with a SatNav instead of the HUD, with the same result. I've also tried reversing the polarity of the connections to the temporary socket, again with no joy (and subsequently tested the HUD again in another car, just in case the reversed polarity damaged it -- but it still works fine). I feel I'm chasing phantoms...

[Bahtatboy]

Edit to add: Both cables from the battery are black sheathed...

[Craven]

Power for a device comes in two parts, Applied voltage which you have but also current, check you have a good earth capable of carrying the current. This would mean a solid mechanical chassis contact not just a twisted wire.
FWIW.

[Bahtatboy]

Power for a device comes in two parts, Applied voltage which you have but also current, check you have a good earth capable of carrying the current. This would mean a solid mechanical chassis contact not just a twisted wire.
FWIW.

Thanks. I secured the earth wire tightly under the screw which holds the earthing bracket to the heater box (well, I think it's the heater box...). But I'll double-check connections next time I try.

[HCA]

Edit to add: Both cables from the battery are black sheathed...

That is OK, but one of those black cables from the chassis will go to a pole that is smaller than the other if negative earth (vv for + earth), or if the older Ford type, will go to a flat pole that is marked ' - ' for negative earth or to '+ ' if positive earth...

[mikealdren]

I would be amazed if a Zetec car was Positive earth, Negative earth became the accepted standard in the 1960s and I don't believe any ECUs will operate on Positive earth.

[Bahtatboy]

Thanks all. It's negative earth: didn't realise that my (any?) multimeter will determine polarity when checking voltage -- a "+" (or, in the case of my multimeter, the absence of a "-") before the voltage reading indicates negative earth when the red probe is on a power source and the black probe on an earth (and vice versa); I also disassembled the panels in the boot (I hadn't realised they were just very close-fitting push fits) and saw that the cable from the negative terminal of the battey was attached to a metal plate embedded in the fibreglass (which in turn, presumably, is attached to the Spyder chassis).

Still didn't sort the initial problem, which I now suspect is caused by the cigarette lighter adapter reducing the voltage to below that required by the HUD and the SatNav (and I'm assuming that the other vehicle -- a new-ish BMW -- in which that same adapter powererd both the HUD and the SatNav, has more advance electrics). On order is a panel including 12V output USB ports, so hopefully that'll sort things.

Next to sort is the amplifier, which I've determined is powered by (presently unconnected) heater rear window cabling. So does that mean that if I want music I must have the HRW on? Whoever did the wiring (or later buggered it up) has introduced some very Lotus-y elements (eg, the clock stops when the lights are on...). Oh joy.

[Slowtus]

Still didn't sort the initial problem, which I now suspect is caused by the cigarette lighter adapter reducing the voltage to below that required by the HUD and the SatNav

When you say 'adapter' do you simply mean the lighter socket itself or do you have something else in line there?

It makes no sense that the voltage would be reduced...best way to check is to measure it though.

[Bahtatboy]

Still didn't sort the initial problem, which I now suspect is caused by the cigarette lighter adapter reducing the voltage to below that required by the HUD and the SatNav

When you say 'adapter' do you simply mean the lighter socket itself or do you have something else in line there?

It makes no sense that the voltage would be reduced...best way to check is to measure it though.

I've now measured the voltage at 3 points:
a) The supply to the cigarette lighter socket, without the socket actually attached: 12-13V, as expected.
b) Between the +ve pin of the socket and the -ve inner lining, without the adaptor (plug) inserted: 12-13V
c) As b), but with the adaptor inserted: about 6V.
Given that the HUD requires 8-18V (according to its spec sheet), this would appear to be the problem. However, on further investigation, it seems that (nearly) all USB's operate at 5V, so quite how the HUD is designed to operate via a USB feed but requires 8V is a mystery (or mistake). Although this still doesn't explain why the HUD will work -- with the same adaptor -- when plugged into a modern BMW's cigarette lighter socket (and I can't measure the voltage when the adaptor is plugged into that, because I can't get behind it to access the +ve terminal). Any auto electricians on here who can shed some light? Or is it the case of British, German and Chinese volts being different?!

The only glimmer of hope is that the same HUD product now ships with a power lead that has an adaptor as part of the lead, whereas mine is a USB-C / Mirco USB lead and a separate adaptor. I've asked the distributor if they can help, and am awaiting a response.

[HCA]

USB-C is designed to supply 5, 9, 12, 15 or 20V at 3A or, in some cases, 5A. Of course the actual voltage depends on the power supply and design.

the adapter you are using will in all likelihood be a bog standard '5V' reducer type as this is the voltage required to charge most comms devices. Yhese adapters are ones seen on the racks in petrol stations everywhere. This 5V will extend to 8V if the connection conditions are right.

Your visual device, if marked 8 - 18V, should be hardwired to a car of 12V, either directly or through a CLR using a straight through circuit plug.

I would imagine that the contacts of the CLR in your BMW are far superior to those in the Elan. Ideally replace the CLR in the Elan with a modern one (NOT a cheapo from ebay...) or with some emery paper around your finger, score the contact points then lightly smear with some vaseline.

[Bahtatboy]

USB-C is designed to supply 5, 9, 12, 15 or 20V at 3A or, in some cases, 5A. Of course the actual voltage depends on the power supply and design.

the adapter you are using will in all likelihood be a bog standard '5V' reducer type as this is the voltage required to charge most comms devices. Yhese adapters are ones seen on the racks in petrol stations everywhere. This 5V will extend to 8V if the connection conditions are right.

Your visual device, if marked 8 - 18V, should be hardwired to a car of 12V, either directly or through a CLR using a straight through circuit plug.

I would imagine that the contacts of the CLR in your BMW are far superior to those in the Elan. Ideally replace the CLR in the Elan with a modern one (NOT a cheapo from ebay...) or with some emery paper around your finger, score the contact points then lightly smear with some vaseline.

Thanks Hal. The only straight through circuit plugs I can find don't have a USB port, so I can't figure out how to get 12V to the Mirco USB that fits in the HUD...

[Bahtatboy]

USB-C is designed to supply 5, 9, 12, 15 or 20V at 3A or, in some cases, 5A. Of course the actual voltage depends on the power supply and design.

the adapter you are using will in all likelihood be a bog standard '5V' reducer type as this is the voltage required to charge most comms devices. Yhese adapters are ones seen on the racks in petrol stations everywhere. This 5V will extend to 8V if the connection conditions are right.

Your visual device, if marked 8 - 18V, should be hardwired to a car of 12V, either directly or through a CLR using a straight through circuit plug.

I would imagine that the contacts of the CLR in your BMW are far superior to those in the Elan. Ideally replace the CLR in the Elan with a modern one (NOT a cheapo from ebay...) or with some emery paper around your finger, score the contact points then lightly smear with some vaseline.

Thanks Hal. The only straight through circuit plugs I can find don't have a USB port, so I can't figure out how to get 12V to the Mirco USB that fits in the HUD...

I suppose I could just cut the Micro USB lead, and hardwire the Red and Black cables...

[HCA]

Thanks Hal. The only straight through circuit plugs I can find don't have a USB port, so I can't figure out how to get 12V to the Mirco USB that fits in the HUD...

There are plenty around. Here is one that even gives you some ambient lighting...

https://www.mobile24.fr/shop/chargeur-v ... gJYw_D_BwE

I suppose I could just cut the Micro USB lead, and hardwire the Red and Black cables...

If you are sure these are the power wires, yes.

[Bahtatboy]

Thanks Hal. The only straight through circuit plugs I can find don't have a USB port, so I can't figure out how to get 12V to the Mirco USB that fits in the HUD...

There are plenty around. Here is one that even gives you some ambient lighting...

https://www.mobile24.fr/shop/chargeur-v ... gJYw_D_BwE

I suppose I could just cut the Micro USB lead, and hardwire the Red and Black cables...

If you are sure these are the power wires, yes.

Right, I have Schrödinger's volts. Went through various tests with (and without) new CLR's (not with straight through plugs, haven't bought those yet) -- the upshot is that as soon as anything is connected to the system, the voltage drops. The new CLR's indicate the USB output: the voltage to them is around 12V, but the output is 6-7V -- not sure if that's a feature or a fault. So, put those to one side: I cut the Micro USB lead: only black and red wires, and first checked that they'd power up the HUD by just touching them on the inner pin and internal shell of a 240V to 12V CLR transformer: all good, even without a secure connection. Made a secure connection of the USB +ve cable to a feed from the fuse box, and the -ve cable to a good earth (first testing that the fuse box point and the earth produced 12V): without the Micro USB plugged into the HUD, still 12V -- but plug it in, no response from the HUD, and the voltage across the connections dropped to 6V. Back to the 240V/12V CLR to check that I hadn't blown up the HUD, but all good. Then located a heavy relay in the footwell, with a substanial power feed; checked the voltage between that and the know earth: 12V. Tried that feed with the same set up as above, with the same result. So there's 12V output, but as soon as something is connected, it drops to about 6V, even bypassing the fuse box.

And although I can live without the HUD, I want to wire in a radio, but it's pointless starting on that until I can determine what cat/gremlims/faults/features are preventing even a tiny HUD working.

[HCA]

You have me on your Shrodinger volt thing! Not sure what it is. But no matter. what you are generally saying, I think, is that no matter what you do or where you make a connection, the voltage drops to 6V.

IF this is the case, then you have possible serious problems with the car as it indicates that anything on the car will drop to 6V. Does the car start? Do you have headlights etc? On what you say, it is doubtful - iF that is, the drop applies to the whole car. It maybe that there is a drop just on the couple of circuits you are using.

Voltage drop is complex and requires testing a circuit at various points, it also requires that everything is resistance tested. Two contributing factors to voltage drop: Earthing and Corrosion with Earthing head up the list. Start at the battery earth and clean the metal down to bright steel. Do the same wherever the earths are for the crl circuit