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Changing to Neg Ground - Fuel Pump?

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BrandonBJ8

Jedi Trainee
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I'm changing my car to negative ground today. One thing I'm not sure about is the fuel pump. It's the new SU model (AZX-1307) that is polarity sensitive. I actually have two of them (one off the car and one on) because we had issues with the polarity when first installing. It says in the box that BLACK tape means it is negative ground. Both my pumps of the BLACK tape but the one connected to the car is running fine so it must be a positive ground. We may have converted it but I don't remember. Is there a way I can check? What about the other new one I have lying around, how can I check that if it is negative or positive ground?

Thanks!
-Brandon
 
black tape means neg-ground. The only way to check I believe is to open the pump and see the polarity of the capacitor (or the conection of the input resistor if the pump is the new transistorized type).
If you do not use the right one, the car will run, but eventually will stop when the relay becomes too hot. It means the car runs, but it is not reliable.
 
What will I be looking for when I check the polarity of the capacitor to see if its positive or negative? (I believe one or both of these may have been converted to positive.)
Thanks!
-Brandon
 
Here are two pictures of it taken apart. This is the one that is NOT in the car. I'm hoping its negative so that I can just swap them out.
 

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Hi Brandon, If the 1307 AZX pump is "New" recently purchased it is not polarity sensitive. Similarly, if the one on the car is operating the only way I know to determine its configuration is to, remove the end cap. If you see a small black component with red and black leads or a capacitor attached and it isn't melted it probably is also of the newer configuration or of the proper configuration for the car .-That's best I can tell you.---Fwiw--Keoke
 
On the box, it says that it is polarity sensitive.

Looking at the 2 pictures I posted (this one is the spare), can you tell if it is positive or negative ground?

Thanks!
 
Both pictures say the pump is Negative Ground.---Keoke ?
 
Here is a picture of the pump that is on the car. It looks to be the same configuration as the spare. If they are the same, that means they are both positive ground since the car is positive ground. If this is the case, can I reverse the polarity on the pump?

(Is it possible these are both negative and that the negative pump on the positive car is working? Is that possible?)

Thanks!
 

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Nope color coding of the diode protective device in both pumps say negative ground. However, all that white stuff on both diodes may suggest they have perished from being connected the wrong way around. Consequently, they are no longer polarity sensitive but will have limited usable life spans because sever arching at the points will occur.---Keoke-?
 
Brandon we better do some checking here. I am basing polarity on standard universal color code. It is possible that the vendor at that time to keep installation personnel from being befuddled used a standard wiring procedure but had two different diode configurations.. Therefore, we need to unhook the diode at the red lead and check its polarity. Using an ohm meter, check between the re and black wire. If the meter shows an essential short circuit when the meter's positive lead is connected to the red wire and then shows a virtual open circuit if the leads are reversed, the diode is OK and the polarity is set for Negative ground. If the results are just the opposite then the polarity will be set for Positive ground. ONTOH, if the meter shows a virtual open circuit in either configuration the diode is pershised and the pump is unprotected but insensitive to gound system polarity.--Keoke
 
I tested it with the multimeter and was getting a reading (3-4) for both ways (red to red, and red to black). I take it this means the diode is bad.

I think that these are both negative pumps. Would I be better off swapping out the pumps when I change to negative ground so that I am running a negative pump? Or will the current pump work? If I do swap out the pumps, do I need to do it at any certain time of the conversion or does it matter?

As always, thanks Keoke and others!!

-Brandon
 
Well it seems that those diodes is cooked. You have some options: 1] Remove the existing diodes and replace them with new properly polarised ones. 2] Remove the existing diodes and obtain 0.047 Micro Farad Nonpolarized Capacitors and connect them across the pump's "Points" 3] purchase a new Negative ground electronic pump. My personal preference would be Item #3.

Economics says use Items #1-or- #2--There you have it.


When you do the deed is simply up to you. /bcforum/images/%%GRAEMLIN_URL%%/yesnod.gif-Keoke-AZ /bcforum/images/%%GRAEMLIN_URL%%/cowboy.gif
 
Now I think the spare pump (first 2 pictures) is negative ground. It's never been installed in the car and the diode looks black/new. Can I use this one since I am converting the car to negative ground? Thanks!
 
I would check the diodes polarity to be absolutly sure how the pump is polarised because my earlier suspicions regarding the availability of two diode configurations is true. Rather than taking it on blind faith.-----Keoke-


Yes, it must be disconnected at one end to check it out as indicated in the earlier response.
 
i believe they are negatibe ground. Yes, thry work in a + earth car, but the realibility will be low because overheating caused by the voltaic arc (it will probably stop working after some time of running, and recover after stopping for some minutes).

Probably your diode is burnt. You might want to replace the diode for a new one that you can buy from moss
 
It still works now that I've changed to negative ground, but I think I'll just swap the diodes out and put the new diode on the car. That should hopefully prevent any disasters down the road! Thanks everyone for their input on this thread!
 
Keoke is correct.

On some of the more recent pumps, SU replaced the arc suppression capacitor with a diode. This diode makes the pumps polarity sensitive.

The SU pump diodes come in two configurations. One for positive ground, Moss #377-135 & one for negative ground, Moss #377-145.

The difference is slight but you can sometimes tell. Note that there should be two different types of terminals on the two diode wires. Unless they have been previously modified.

The diode for negative ground pumps has a ring type terminal on it's red wire that goes to the pump power supply wire & a spade type terminal on it's black wire that goes to the pump internal winding connection.

The diode for positive ground pumps has a ring type terminal on it's black wire, that goes to the pump power supply wire & a spade type terminal on it's red wire that goes to the pump internal winding connection.

In both above cases, the diode is connected with it's cathode to the positive terminal. A diode will show a low resistance when connected with positive on the anode & negative on the cathode. It will show a very high resistance when connected with positive on the cathode & negative on the anode which is the intended connection.

If the diode is good, you can just interchange it's two connections to make it work either way, although the ring & spade terminals will be on the wrong wire colors.

All three of your pics show the supply terminal to have the red diode wire connected to it & so would be presently connected for negative ground.

If you connect these pumps to a positive ground system, the diode will cause a short circuit for a few moments & then blow open circuited. The pump will still work with the open diode but there will be no contact arc suppression & the contacts wont last long.
 
Brandon,

If you have an ohm meter, hook it up to the diode first with the meter leads in one combination, then swap the meter leads. If it indicates an open circut with the leads connected either way, then the diode is damaged ( burnt open ). If it read a low resistance one way and high resistance with the leads swapped, then the diode is good.
It is unlikley to, but it could read low resistance in both directions. That also means it is damaged ( internally shorted but not burnt open ).

No sense it throwing it out if it is still good.

Ed
 
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