I have had the battery off the car whilst stripping paint and priming etc.... but thought it would be good to turn the engine over and run it for a while to keep things in good health etc.....
I had the battery on the bench to charge it and then put it back in the car but very stupidly put the negative lead to positive terminal and positive lead to negative terminal.
I didnt turn the key as I was checking other things when I realised what I had done.
I noticed that there was a smell of smoke coming from the alternator area and the tin on top of the engine in that area was warm so suspect there is a connector to the alternator under there?

I put the terminals on the right way around and tried to start the engine but it appeared the battery had drained?

I recharged the battery overnight but wouldnt start, again the battery seemed low on charge
Apart from seemingly screwing the battery, is there other damage likely to have occured

cheers
David

There is almost certainly other serious damage if you smelled smoke.

There is no simple answer. If you're not experienced at electrical troubleshooting or lacking for patience I would recommend that it go to an electrical specialty shop.

You don't mention if you have original fuel injection of if the vehicle has been switched to Carbs. At this point having Carbs would work in your favor since there is a possibility that the fuel injection ECU (amonst other things) just got fried.

If you have a schematic, patience, and some experience with electrical items, you'll just have to start tracing wires, checking for blown fuses, looking for blown relays, searching for burned wires, etc.

I've been there, done that. It kills diodes and possibly more in the alternator... likely have to replace it... easy to do on a T4, PITA on my /6....

I'll start with a new battery and replacement alternator (when I find one) and take it from there
thanks for the replies

The radio is likely toast but most else on the dash end is OK I'd think.

I have OCD triple checking, then checking again when it comes to connecting batteries. Always the ground is the first off and last on connections.

Is it safe to put a new battery on the car and try it?
If the alternator is toast, what effect would trying to start it have?

I would not start by installing a new battery and hoping for best given that you smelled smoke.

You likely have shorted wiring now either from melting and possibly from diodes. When diodes fail they usually go open but I wouldn't risk it.

At least start by using an Digtital Multi Meter to see if the battery + is shorted to ground.

After that I wouldn't even consider attaching the battery until you've inspected all the engine harness wiring starting with the alternator and the ignition coil.

Don't put a battery back in there until you tested all wires ...

You don't want to run current through something like this:

@SirAndy @Superhawk96
Thanks for the pointers guys, I will heed your advice

Just one additional thought:

IF the alternator is new, and IF has never been used since it was installed, then it could be an issue with the + threaded stud touching the alternator tin. It's often too long, and this would short regardless of polarity.

Do not install the new battery. Pull the alternator and check for damaged insulation on the primary wire.

I think You shot the diodes of the altenator.They resist this only a short time.

will do Dylan, things were going so well !!

I have found some one close by that repairs alternators so I will get it over to him

Ok, if you need an alternator or harness let me know and we'll get one shipped.

This is a great learning opportunity to get to know your multimeter. Spend time learning to test electrical functions. You’ll be better prepared the next time you let the smoke escape from the wires.

Electricity is somewhat of a mystery to me so bear with me.

I don't understand how switching the + and - leads can cause a dead short and burn up wiring. I can understand how polarity sensitive devices (like a diode) might be harmed but why wiring?

Also, there is so very little that gets power with the key in the off position. How would the radio (for example) be damaged?

The way I see it, any circuit that is switched and the switch was off when the battery was connected backward should be fine. Any circuit that is always energized is subject to damage. Modern radios often have a switched and unswitched circuit and of course, any radio can be wired either switched or not.

You are a diamond geezer (as they say in the South)
thanks Dylan, let me see how it tests out

cheers

No radio fitted at present so don't have that to worry about

Most basic answers:

1) Since chassis is assumed to be ground, it can basically source infinete electrons (in theory) and those electrons moving = current. The chassis ground strap between the body and the transmission for example is about 1" wide and is pretty thinck braided wire that can easily handle several hundred amps drawn though it upon cranking and to run the coil and alternator. When the connections are switched (+ for negative) now all the positive wires become ground. Current goes looking for a ground path where ever it can find it - electricity always tries to follow the path of least resistance. If that path happens to be a small gauge + wire that was only sized for 1A but is now trying to support 10A of current draw being drawn through it, poof it melts.

1a) IF, every circuit had an equally sized positive and negative (ground) wires, this situation wouldn't occur. However, that isn't the way cars are wired. Often there is only a positive wire that feeds the circuit and the ground path is provided by "chassis ground". Now you have an asymetric sizing between positive and negative current paths. Positive is limited by wire size. Chassis ground is very large.

2) Electronic componenets like diodes. A diode is only designed to flow current in 1 direction. Diodes have a characteristic called Peak Inverse Voltage (PIV). A diode will resist reverse current flow up to the PIV but beyond that it will "leak". The rate of leakage depends on how much higher the PIV is and whether or not the diode overheats and fails open. As it continues to "leak", allowing current to flow backward, that situation becomes a basis for situation #1. Small gauge + wires can melt since they weren't sized for that current. Really big and well heat sinked diodes (i.e. the alternator) can have some substantial leakage before the overheat and eventually fail open. What circuits flow current in reverse up until the diode opens is up to the electrons trying to find their way home is somewhat of a guess

You are correct that if a circuit was completely turned off and has no circuit path, it would be unafffected, unless there are diodes in that circuit that fails, and, creates a path where otherwise it would not have existed when connected properly.

Since OP was from England and now that some of the sting of the situation has worn off, I can now cut him some "extra" slack.

Some old British cars were actually reverse ground. Early Jag's were like this and I'm sure they weren't alone. In this case positive terminal does go to the chassis. Perhaps he has a collection of Jag's and had a momentary lapse when connecting the battery. Cheers Mate!

The Lucas - Prince of Darkness moniker didn't come without justification.

I wrote this for a friend a few years back when he got his first Jaguar...

Our Father Lucas who arth in Hell,
condemned by thy name.
Your darkness will come,
your shortcurcuit unfound,
positive earth as standard.
Give us today our burning harness,
and forgive us our use of heatshrink,
as we forgive those that use fuses.
Lead us not into electronics
but deliver us from logic.
For the darkness,
the nonexistant spark and the mysterious smoke are yours.
Now and intermittently.

Ohm.

Cannot resist..........

Years ago I met an older gentleman who's last name was "Lucas". He said that he had just retired (sold) a few auto dealerships in the northern SF area specialized in English cars.

I said that he must be tired of hearing the Lucas Joke. He stated that he had never heard it. So I told him....

Why do the English drink warm beer?

Because Lucas makes refrigerators too!

He was not amused, a friendship was not made.....

CTC911CTC

thanks Superhawk but no slack is deserved in this instance
It was a monumental moment of fuckupery
I have had the battery off and on a dozen times, have 20 years of restoration experience and 35 years of diy mechanics so have no excuse.
I bet I dont do it again

The English language evolves through creative combinations of words in common usage. You sir, have skillfully woven such an example that should become a permanent part of the lexicon: fuckupery!

I can see the scene at a spelling bee clearly: Fuckupery - F-U-C-K-U-P-E-R-Y - Fuckupery.

Or better yet, the contestant asks, “Can you use it in a sentence?”

Classic!

thanks Kelty
it looks like you reside in Townsend?
that's my surname
how about that !!

so the latest...

I tracked an alternator down over here and fitted it at the weekend

With the ignition on I can hear the fuel pump running at the front, when I turn the key to start it is very slow to crank and is not firing, its as though the battery is virtually flat
I swapped out the battery for a spare that I believe to be good but the same result.

Looking for suggestions as to what else to check please

I am an electrical numbskull and whilst I have a circuit tester I have no clue how to use it.

Assuming one or both batteries are actually charged it sounds like a grounding issue. Check all your electrical connections to make sure they are snug, but particularly check connections to starter and all your grounds. Specifically, make sure you've got the ground strap snugly attached from rear of gearbox to a clean ground point that's on the underside of the trunk. Also check to make sure your battery ground is clean and snug, and that the actual negative terminal is snug to battery terminal -- but do not overtighten (else it can stretch and ruin the clamp).

Good luck.

Think of the electrics as "Plumbing for Electrons" all of the connections need to be tight and clean or you will have 'leaks'.

I would start with all of the POWER connections. Start with the battery ground. How solid is the metal around the connection on the side of the engine compartment? If the lug on the compartment wall is connected to rusty metal, in essence, this is one big resistor and the NEGATIVE needs to be SOLID and consistent at every point it is used.

On this, a VOM might show zero ohms between two chassis points, however, when 90+ amps are being drawn, the current flow characteristics can change. RUST or loose connections.

Clean the Negative connection! Super clean and tight.

On the Positive (+) side, the cable from the battery to the starter must be in good shape. As a question of maintenance, many people replace this cable for a variety of reasons that have to do with age of a plumbing part and it getting leaky.

Make certain that the connection from the battery to the starter is solid, clean and tight.

The starter, of course, has two components - solenoid and the starter motor. if you are certain the cabling is solid - replace the starter.

Let us know how things turn out!

thanks guys, I will follow the pointers given and let you know how it goes

About what could happen if the battery was reversed; check out the 914 charging circuit diagram below. With the battery connected correctly as shown, all the diodes in the alternator block current from the battery.

When the battery connection is reversed, the diodes are forward biased and shorted across the battery and will likely be damaged.

so it should just be the alternator that is kaput?

I have had an hour checking the negative battery lead, the earth strap, live feed to the starter motor and any other wires to the body for good connections and earths. I didnt see anything untoward but cleaned them up in any case. No improvement, the starter barely responds.
I did figure how to get a reading from the multi meter and it showed the battery to putting out 12.5v
Is there a way of testing the power getting to the starter and the alternator?

Agreed, many of those diodes are either welded shut (unlikely) or toasted open

I would get another battery - i know you have tried another - however, this sounds like the battery is not juicy enough.

Try this test, this may take two people: put the Volt meter on the battery and then when you grind the starter what is the voltage? If it falls close to zero - try another battery. If it stays above 8-9 volts - there is a wiring or starter problem.

GOOD LUCK!

best way to test provided you have a strong battery,the starter pulls huge current,an old battery will tip over really fast with this load and a fully charged one will indicate a bad starter as appears you have checked all connections.
914 starters are pretty strong ,strip down and service it ,pretty easy.

Considering how often I have seen this happen on 3 bbs, I am surprised the SAE doesn’t develop a standard where batteries have round and square or star shaped pegs and the connectors have similar so there is never a screwup unless really drunk.

Good luck to the OP and yes your alternator is toast.

I got the Mrs to turn the key whilst I checked battery volts, one battery dropped from 12.5 to 9.5, the other dropped from 12.5 to 10.6
does that suggest healthy battery and a dodgy starter motor?
can a starter motor be tested on the bench with a battery?

If the wiring is solid, all connectors tight and clean - I would move to the starter mother/solenoid as the culprit Also, is the starter fully engaged? Does the motor turn? Makes that Errr,Errr, Errr noise? Or, do you hear clicking? Errrr,,, Click,Click,Errr,Errr,Click,Click???

DOUBLE CHECK THE WIRING -please,,,,,,,,

its a very slow errr......long pause...... errr .......click


I have looked the wiring over and cant see anything untoward
As the fuel pump can be heard running and there is small sign of life in as much as there is power getting to the starter but either not enough to turn it over or the starter has a problem, could there be anything on the relay board that could have been effected?
I notice there is a circuit board on the underside, could a track have been burnt out? (there isnt any sign to suggest this, i am just fishing for ideas)

No. Since the solenoid engages when you turn the key to start the only circuit relevant on the relay board is good.

The connections you haven't tested are where the battery cables are crimped onto the terminals at either end. These can and do corrode internally. I've used jumper cables from the battery terminals to a ground near the starter and the starter battery cable post to provide an alternate current path. If the engine spins faster you have a cable problem.

If the starter was working before this issue I would look into this before pulling or replacing the starter.

I would run the jumper cable from the negative terminal first - battery to starter - this will confirm that the chassis is working as a ground conductor or not.

Next

If there is no change, take the cable off completely

Then the Positive side:

Connect the jumper cable to the starter on the big nut, where the battery cable connects (once this is done the other end of the cable is HOT - make sure it is not touching anything), then connect to the positive - Double Check- lug of the battery. Then turn the key!

If there is no change to in either test,,,,this is getting interesting!

My advise maybe suspect as electrical work is a real art on older cars as you are always chasing issues.
You could try to crank the starter manually by jumpering the hot lead to your yellow solenoid wire,try that and may prove you have an ignition switch issue which is very possible with these cars.
Yes you can bench test the starter after you have done the above,

I guess I can make this easier to get the jumper leads to the starter by putting the battery under the car? so not having to thread them down and around and also not as likely for the positive to contact something it shouldn't?

I am clear on which is the positive for the starter

could some one show which is the negative or is it obvious once I get back under and take another look?

Many thanks for the pointers chaps

Click to view attachment
I took a photo from ebay, I am guessing the negative is the terminal that is not the positive

Technically speaking when connecting and disconnecting jumper cables the negative terminal is the last fitted and first removed and not connected to the battery post.
The reason being if there is a mistake with polarity or a dead short there is the potential for sparks, if this happens at the battery there is a possibility of an explosion caused by sparks igniting battery gases.

We still have some conceptual work to do.

The entire car - everything metal is negative. So, the negative lead should be connected to the starter chassis or a point close to the starter. See the red circle in the picture.

We are testing the connections from the neg term on the battery, through the car to the starter, there is a ground strap that connects the engine/trans to the chassis - this may be a problem.

The lug closest to the starter body is the positive power for the actual starter motor. The lug towards the top of the picture is the connection to the battery. The bendix (small cylinder above the starter motor) is a contactor which connects the 2 lugs together electrically to turn the starter motor. The bendix also pushes out the gear which engages the flywheel so the starter motor will turn the flywheel.

The small electrical tab on the bendix is the power (from the ignition switch) to power the bendix.

Personally I wouldn't try to connect any wires or jumper cables to the starter. I would inspect the wires and if anything, measure the voltage on the lug from the battery when the starter is engaged.

Once you have the voltage at the starter, do the same measurement at the battery measuring from the positive terminal CLAMP and at the actual battery terminal. This will test the clamp and wire to make sure it is electrically sound.

Also check the ground strap on the battery to chassis AND the ground strap on the transmission. All cables should be clean and secure.

so I connected a jumper lead to the negative battery terminal and the engine and the starter sped up quite noticeably although not enough to fire up
I then ran a jump lead from the positive post on the starter to the positive to the battery, the starter remained at the increased speed but the engine didnt fire
suggesting a negative lead to battery problem
I also wonder about the non firing issue, could there be coil damage?
I swapped batteries over but to no effect and now have the better of the 2 on charge as it started to struggle.
I also tried the negative jumper on the starter itself to see if that was grounded, it ran at the improved speed but the doesnt sound to be any firing, I could take a plug out to see if there is a spark but I dont have a helper any more as the Mrs has fallen and broken her wrist