Cant start my NB after battery replacement

Technical Area Engine, Transmission, Exhaust etc
1
  1. My model of MX-5 is: _NB
  2. I’m based near: _ Worcester

The battery in my 1.8 NB wasn’t very old and had no issues, but to be on the safe side when I put it away for the winter I attached it to a solar battery conditioner. Only a couple of weeks later I went to use it and the battery was completely flat. I removed it and it wouldn’t charge on the bench, neither could I jump it. Bought a new battery which I know is charged but still nothing (not even a click, no lights, totally dead). Have checked main fuse and its OK so am now stumped, any ideas guys?

2

Have you actually measured the charge in the replacement battery?

1 Like
3

Did you take the plastic caps off the new battery lugs before attaching the cables? (It happens!)

4

I did yes.

5

Yes its brand new but I also put it on charge overnight just in case it had been on the shelf for a long time. Multimeter shows 12.v.

6

It’s connected the right way round too? The terminal with the grey cover on the positive post.

Does the horn work?

7

No nothing at all works. Wondering if its related to the immobiliser but I believe in these cases other stuff like interior lights should still work.

8

If nothing works it’s not immobiliser related. Unless it’s had an aftermarket thing added… I’d still be surprised if an immobiliser cut the whole electrics.

9

Yeah thats what I thought. The immobiliser is standard, I wonder if there is another fuse somewhere, I did see this mentioned online but it wasn’t clear what model of MX-5 they were talking about.

10

I think you might be refering to the window and central locking fuse behind the trim panel above the battery in the boot. Worth checking to see if it is okay but unlikely to be the cause of your dead electrics.

11

What do you mean by “standard”? Is it a UK spec car? In that you don’t have to do anything other than put the key in the ignition switch and turn it.

12

That doesn’t sound right to me. I think that a fully charged battery should be reading more than that, somewhere around 13v.

13

Yes its completely standard. A couple of months ago the battery in the keyfob went and following the advice on here I was able to pair the fob again so it seems like a normal NB.

14

Are you able to check the voltage at the big terminal on the back of the alternator? The thick wire held on with a 12mm nut.

15

I will do later. But as I say it was 100% OK when I parked it two weeks ago so whatever has happened has been caused by the solar powered battery conditioner. Baffled.

16

Or something has gone wayward during the battery disconnect/reconnect/replacement. We need to ascertain why the 12 volts from the new battery is not making its way to anywhere on the car.

How certain are you that the main fuse really is OK? You could also check for voltage at some other fuses.

1 Like
17

Bad earth maybe, once had a Metro Turbo and one day it just died, not a thing worked on it. Traced it to a corroded earth connection ?

1 Like
18

You tried jumping from a running car?

good battery V =12.7ish

12v would be about 20-25-%charged or flat to most people.

When charging about 13.5 or above

When cranking , should be above 10.2

When you say “nothing”, are there any interior lights, dash lights, horn, anything?

When removing the old battery did you dislodge the earth strap that attaches to the chassis next to the -ve terminal?

19

That’s what aa are for call them and let them diagnose fault.

20

Have you tried the original battery back on the car? The one that was working without problems, which you took out in favour of a new battery.

Which battery did you choose for the replacement?

I’ve always stuck to the recommended, ie., Westco.

Fitted with an isolation (screw) switch to the Westco battery (with breather pipes), to prevent draining energy to maintain ECU etc.when not on charge.

IMG_1529
IMG_15291920×1584 686 KB

Along with an ‘Optimate 4’ battery charger unit.

image
image2905×3546 963 KB

image
image1920×2694 946 KB