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MG MGB Technical - Alternator Swap- now no start

I swapped the Lucas alternator on my 73 BGT for the Bosch upgrade. I had some problems with the mounting and at one point had quit to go to work. I was going to move the car (alternator plugged in but not attached to drive belt) Car started but then died. Now it wont start at all. I finally finished the alternator install but car still will not start.
Any ideas on what I fried?
william fox

William. The original alternator and the new alternator should be hooked up in a similar manner. One line going to the ignition warning light, the heavy brown lines going to the main starter terminal and the ground is the alternator case. First place to check, in your case, is the main starter terminal to make sure the connections are both good and tight. Then, get your wiring diagram enlarged to at least 150% and start tracing circuits to see what could cause the problem you have. Does it crank over? If so, is there spark at the coil lead? If so, is there spark at the spark plug lead? Is the fuel pump working? Check out what problems you actually have, examine the wiring diagram to see where the different systems come together, then start checking for current and moving forwards or backwards until you find the problem. Just went through an electrical problem and solved it in an hour. If I can do it, anyone can. Les
Les Bengtson

Thanks Les..the eltectrical connections were a straight swap- in fact my old alt plug fit right into the new Bosch unit. The car did start once, ran a few seconds, then died. I had the alt plugged in at that point but is was not bolted on- just sitting in the engine bay. Now the car cranks, and is getting fuel, but wont start. I havent been to check for spark at the plugs, etc yet.....thought someone may be able to tell me straight out that I fried something
william fox

William. I do not know that you fried anything and am not sure that there is a true cause-effect relationship here. Check the ignition circuit to see if you have spark. If not, trouble shoot the low tension circuit to see if you have power going to and through it. You might also want to make sure that all of the brown wires are hooked up to the main starter terminal. There should be at least two from the alternator and at least one more going to the fuse box and, perhaps, other areas. Just check out the systems and we should be able to figure out what the problem is when you have more data available. Les
Les Bengtson

William,

Did you disconnect the battery(ies) when you worked on the alt? If the you moved the car with the alt unmounted and it happened to rub on the wrong part it may have grounded something.

Luis
Luis

I did some checking and found I have no power going to the coil. The two white wires coming off the #5 terminal are dead. I back tracked the + terminal on the coil through the schematics everything connected throug the white wire seems to work, tach, ignition light, fuel pump, starter relay, and items controlled by the wiper stalk. The schematic shows a wire from the junction under the dash that branches- one to the fuel pump and one to the fuse block but I cant seem to find this splitter. I only find the one under the dash that feeds power to the wiper switch, ignition light, and this branch that feeds the fuel pump and fuse block. I jumped the #5 teminal off the brown wire below and I find I get power at the coil and the - terminal of the distributor. Still wont start though....All other circuits seem to have power except my turn signals (Hazards work)and the coil.
william fox

How did you tell your tach worked if the car won't start? The starter relay isn't connected to the white. The items on the wiper stalk are powered from the green (same as the turn signals, brake lights, reverse lights, gauges etc), which gets its power though the fuse that is connected to the white. Unless you meant the overdrive switch. The wiring varies according to whether you have the later 73 with the ignition switch 'hard wired' into the loom or the later where the column stalks are connected to the loom via multi-way plugs and sockets. But in both cases the white from the dash splits off to the fuel pump and the fusebox at a double connector in the mass where the main loom connects to the body/boot loom, and these are located where the firewall meets the RH inner wing in the engine compartment. But if you linked the brown to the white and it *still* didn't start then you obviously have something else wrong. When you had power to the coil did you check for spark?
Paul Hunt

Paul,I presumed, looking at the schematic, that the white came through the tach to the ignition that the tach would be working since have power there.. I have a 73 that has all the connectors under the dash by the steering column all the white are powered by one. The schematic shows another branch further along that splits one to the fuel pump one to the fuse block (Bentley guide diagram 13 I think). I didnt check for spark when I jumped the wire but will later- duty calls for now.
william fox

OK, problem solved. I found a loose connection in the white wires in the bundle just inside the engine bay by the bulkhead and restored power to the ignition system. A little trouble shooting revealed dirty contacts on the points. Starts and runs fine now. I'm kind of surprised at the outcome as these points were replaced just 3 months ago and have only seen about 500 miles of use.
william fox

William. Glad you got the problem solved. Les
Les Bengtson

Do you ever sleep Les?
william fox

Hi,
Points?Points? Put in an electronic ignition system and join the 20th century. Best $100 you will ever spend on your B. Points are perfect when they are first installed, from there on it is all down hill until they need readjusting or replacing. Points are in the same class as buggy whips. I am surprised that you can still find them available for sale.

Alan
Alan

Maintenance-wise, Alan, electronic ignitions are pretty "trouble" free, insofar as they seldom lose their setting for timing. However, a couple of years ago, I ran across an article in one of hot rodding magazines about a test of points vs. electronic ignitions (points substitutes). Interestingly, the points actually edged out the electronic ignitions up to the point where "point bounce" (inertia) took over the action of the points, producing Slightly more HP! All tests were conducted on the same engine with correct distributors for that engine - just that one was Points and the three others were electronics of one sort or another.

Most of us would not notice the power differential (something like 3 hp out of 350+ horses this test V-8 produced) so perhaps it is a moot point, but technically and empirically, it is sure to to get the engineer's goat. ;-) FWIW
Bob Muenchausen

Yeah, and look how many people carry a set of points as a spare for their electronic ignition ...
Paul Hunt

I still using the same set of points that were in my roadster when I bought it 4 years ago and have logged several thousand miles on it without any problems. The set in this GT were installed last fall and havent been a problem until now when I had to clean them. So here's th math: How many sets of points can I buy for the cost of one Petronix setup?
william fox

This thread was discussed between 26/04/2002 and 01/05/2002

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