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Hi all...I need help. I recently replaced the alternator on a 1978 MGB. The alternator is the 3 spade plug type with fat center spade and two narrow outer spades. When installing the new alternator I accidently reversed the plug. All electrics were working fine even though the old alternator was not charging the battery but now I have no turn signals, the engine will not start..I think the fuel pump is not working...what have I done? help please. <font color="black"> </font>
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1978 Eleectrical issues
- Thread starter mgdon
- Start date
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Ed Kaler
Jedi Warrior
Offline
First, not sure if anybody will even try to answer since you have NO name /ubbthreads/images/graemlins/hammer.gif, but:
[ QUOTE ]
All electrics were working fine even though the old alternator was not charging the battery...
[/ QUOTE ]
HOW do you "know" the alt was "bad"??
[ QUOTE ]
but now I have no turn signals, the engine will not start..I think the fuel pump is not working...what have I done?
[/ QUOTE ]
Any number of things "could" have occured.
Do you have Elect. schmatic in Service Work Shop Manual??
Test light?? VOMeter??
/ubbthreads/images/graemlins/cheers.gif
Ed
[ QUOTE ]
All electrics were working fine even though the old alternator was not charging the battery...
[/ QUOTE ]
HOW do you "know" the alt was "bad"??
[ QUOTE ]
but now I have no turn signals, the engine will not start..I think the fuel pump is not working...what have I done?
[/ QUOTE ]
Any number of things "could" have occured.
Do you have Elect. schmatic in Service Work Shop Manual??
Test light?? VOMeter??
/ubbthreads/images/graemlins/cheers.gif
Ed
kennypinkerton
Yoda
Offline
have you checked the fuses? Are you sure the battery is good/charged?
Ok, those are the easy ones to check, and easily overlooked. Always start with the simple stuff. If the old alternator was not charging the battery, and you haven't checked/changed the battery - it's more than likely dead... hence the non-working high amperage stuff (lights aren't that high amp draw).
Things like the fuel pump, turn signal flasher units, and starter relay/solenoid are all sort-of high current devices.
The only thing that doesn't make any sense to me is the hazard lights working - it's on exactly the same circuit as the turn signals... there are 2 flasher units - one for the turn signals, one for the hazards. Maybe one is a heavy duty unit and needs just a bit more current to switch?
Outside of that... Hooking up an alternator wrong will only kill the new alternator (fries the diode pack inside it nearly instantly)... I think you have a dead battery, but the other things not working may be symptoms of:
corroded connectors in the wiring
bad/loose/corroded ground connections
corroded tabs/connectors on the relays (there are only a few) - possibly bad relays.
blown fuse(s)
bad hazard switch (they corrode internally and if you switch it back and forth several times, it may clear up the turn signals... you can also carefully take the switch apart - noting exactly how the parts go back together, and clean it).
Bad fuel pump.
Bad fuel.
several other possibilities, but start at the top of the list (the battery) and go from there. /ubbthreads/images/graemlins/thumbsup.gif
Got a picture of your car you can show us?
Ok, those are the easy ones to check, and easily overlooked. Always start with the simple stuff. If the old alternator was not charging the battery, and you haven't checked/changed the battery - it's more than likely dead... hence the non-working high amperage stuff (lights aren't that high amp draw).
Things like the fuel pump, turn signal flasher units, and starter relay/solenoid are all sort-of high current devices.
The only thing that doesn't make any sense to me is the hazard lights working - it's on exactly the same circuit as the turn signals... there are 2 flasher units - one for the turn signals, one for the hazards. Maybe one is a heavy duty unit and needs just a bit more current to switch?
Outside of that... Hooking up an alternator wrong will only kill the new alternator (fries the diode pack inside it nearly instantly)... I think you have a dead battery, but the other things not working may be symptoms of:
corroded connectors in the wiring
bad/loose/corroded ground connections
corroded tabs/connectors on the relays (there are only a few) - possibly bad relays.
blown fuse(s)
bad hazard switch (they corrode internally and if you switch it back and forth several times, it may clear up the turn signals... you can also carefully take the switch apart - noting exactly how the parts go back together, and clean it).
Bad fuel pump.
Bad fuel.
several other possibilities, but start at the top of the list (the battery) and go from there. /ubbthreads/images/graemlins/thumbsup.gif
Got a picture of your car you can show us?
Dan Masters has provided wiring schematics to everyone. I have yet to find any inconsistencies with his diagrams. The web address is <https://www.advanceautowire.com> Just click on stock schematics.
The Bentley diagram is the one I have found to be the best for a '78 B.
Make yourself a couple of enlarged copies of the wiring diagram. One for reference and one to make notes on as you are checking the circuits. The printed diagram I made for myself is printed on four 8.5" x 11" pieces of paper taped together.
Now start from the battery, check all the components to make sure they are getting the voltage they are suppose to. Inspect, clean and use dielectric grease on all the connections. This may take you better part of a day, but when you are done, you shouldn't have any electrical problems for years to come.
The Bentley diagram is the one I have found to be the best for a '78 B.
Make yourself a couple of enlarged copies of the wiring diagram. One for reference and one to make notes on as you are checking the circuits. The printed diagram I made for myself is printed on four 8.5" x 11" pieces of paper taped together.
Now start from the battery, check all the components to make sure they are getting the voltage they are suppose to. Inspect, clean and use dielectric grease on all the connections. This may take you better part of a day, but when you are done, you shouldn't have any electrical problems for years to come.
I have checked all fuses with a ohmmeter and they are good. After connecting the alternator up wrong...stupid stupid stupid...I pulled it back off and along with the battery, took both and had them checked out. Both battery and alternator are good. I am stumped!
Scott_Hower
Luke Skywalker
Offline
No turn signals, no fuel pump and wont start.... hmmm.
Check ALL of the bullet connections near the firewall just behind the fusebox. When you say it won't start... do you mean wont crank? Or cranks, but wont start. Don't understand how the alt can be hooked up backward, the plug is directional (or at least it is on mine). Not positive, but I think mine has two large lugs and a little one, I dont think it can be plugged in backward.
Check ALL of the bullet connections near the firewall just behind the fusebox. When you say it won't start... do you mean wont crank? Or cranks, but wont start. Don't understand how the alt can be hooked up backward, the plug is directional (or at least it is on mine). Not positive, but I think mine has two large lugs and a little one, I dont think it can be plugged in backward.
Cranks just fine and will run with starting fluid sprayed into it. My alternator plug has a fat spade in the center and two narrow spades on the outer edges. I noticed after the fact it is directional but it can be plugged in either way so not 100% idiot proof. Perplexing hey?
jlaird
Great Pumpkin
Offline
I would guess as well that the fuel pump has gone west or the line has become pluged. Run a hot wire to the pump from the battery and see if it runs. Disconnect the fuel line from the carbs and run some into a jar or something. check the fuel filter if installed. If all seems well check inside the float bowls for lots of trash not alowing the fuel to inter the carb.
kennypinkerton
Yoda
Offline
The only thing I can think of that might be damaged by an alternator pluggedd in backword would be the alternator - specifically the diode pack inside of it. If it was damaged - the alternator would not be able to put out the correct voltage and current to keep a battery charged... It's about $50 for my local alternator shop to fix this problem. All this is assuming the standard Lucas 45 amp alternator for late model MGB's. I have mentioned this above.
kennypinkerton
Yoda
Offline
I believe the other problems are just that - coincidental. I just can't see where the other circuits would be affected by plugging the alternator in backwords.
jlaird
Great Pumpkin
Offline
I say again per above post.
I would guess as well that the fuel pump has gone west or the line has become pluged. Run a hot wire to the pump from the battery and see if it runs. Disconnect the fuel line from the carbs and run some into a jar or something. check the fuel filter if installed. If all seems well check inside the float bowls for lots of trash not alowing the fuel to inter the carb.
Now, if the direct line to the fuel pump makes it work you have electrical distribution problems. Bad connections and or grounds.
I would guess as well that the fuel pump has gone west or the line has become pluged. Run a hot wire to the pump from the battery and see if it runs. Disconnect the fuel line from the carbs and run some into a jar or something. check the fuel filter if installed. If all seems well check inside the float bowls for lots of trash not alowing the fuel to inter the carb.
Now, if the direct line to the fuel pump makes it work you have electrical distribution problems. Bad connections and or grounds.
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