Yeah, I know ![]()
schoolboy error, car won’t turn/start now though most things otherwise seem to work and all fuses look OK (though there are “boxes” in the main fuse box that presumably contain electrical stuff that I don’t know how to check though I do have a multimeter). I have a new battery but it’s not a sealed one, having read that is OK.
Googling has only turned up a burst alternator as something to check…and it being a PITA to do so.
This after spending the car’s value on it (tatty Mk1) to get through the MOT, due to bad luck and bad advice.
Any ideas? I really don’t want to spend a penny on it if I can do things myself, just get it sold, I’ve already lost hundreds on it vs selling it as a MOT failure and cannot wait to see the back of it, much as I loved driving it.
There is a huge 30 amp fuse which will (hopefully) take the hit in the event of polarity reversal. try changing that and I reckon you will come out of it older and wiser but with no damage.
Does it not crank over or does it crank but not fire?
It doesn’t turn at all. I checked all the fuses, but I’ll have a look at the 30 amp one again.
Don’t just look at a fuse check for power on both sides with ya multi meter try and follow the pos feed wiring from the battery to places like the fuse box and the back of the ignition barrel if you still have no joy let me know tomorrow and I’ll dig out my wiring diagrams I’m just about to go out so can’t look right now
Also check the 80amp fuse in main fusebox under the bonnet.Its bolted in with 2 x 10mm bolts and does not pull out like the other fuses.
That’s happened to me twice while jump starting it, first time my fault, second time tire shop’s fault. In both instances, it was the 80A main fuse that was blown. It’s an easy replacement, but takes more work than a regular fuse because it is screwed in (at least it is on the early models; mine is a '93). On mine, I had to disconnect the battery (make sure you have the stock radio’s anti-theft reset code before disconnect), unbolt the fuse box to get to the screws holding the 80A main fuse in; unscrew and replace the fuse; screw it back in, including any wires originally attached to the screw, bolt the fuse box back in place, reconnect the battery cables, and reset the radio. It was a 15 minute job since I did some cleaning around the area as well. The local auto parts stores had the fuse in stock on the shelves.
Hopefully your simple and inexpensive repair will resolve your issue as well.
Ah, that’ll explain why I couldn’t get the 80A one out. Anyway I popped the top off and it’s fine.
The cooling fan one may be gone, but why would that stop it turning?
I’ll look at following the +ve next!
As GandolfsTwin mentioned in post #5 above, don’t just look at a fuse and assume it’s working because it “looks” okay. A fuse can be blown but still look like it’s okay. Removing and double-checking that 80A fuse may save you a lot of time, pain, and frustration from checking the rest of the electrical circuits. ![]()
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Steady reading of zero ohms on your multi meter? If so fuse is intact.
Flashing zero on your multi meter indicates open circuit, fuse blown.
Well this isn’t apparently going to fix itself! Not yet had company to check voltage with key turned.
From another forum, “The damage? Alternator, starter, one battery cable and some fuses”
and http://www.mbclub.co.uk/forums/electronics/169653-connected-battery-wrong-way-round-help.html
If anyone has any other ideas, they’re welcome!
The problem is that solid state (transistorised) electronics which are connected when you turned the key will blow faster than a fuse can if subjected to the wrong polarity supply. This would include the ECU, dashboard electronics and charge control in the alternator.
If you have comprehensive insurance you might be able to make a claim.