charging problem

[JakesCarCare]

Hello again on a 1981 911 couple a customer brought saying the battery light was on we asked him what happen and he actually changed his battery and put the positive on negative side on and vice versa on the battery which fried the alternator wire and much more wires not every thing works but the battery light is on it was charging at 11.3v so my boss said he could of fried the voltage regulator so we went ahead and changed it started the car check the stat on charging and now its at 13.5 and the battery light is on... now in that picture below the two white connector towards the bottom next to the black connector when its unplugged the fuel pump runs and theres no spark but with the connectors plugged in the pump doesnt runs and theres spark not if i take the brown wire off of the connector on the right side and plug it in the fuel pump runs and we have spark the one ground isn't allowing us to have both spark and have the pump running at the same time what could it be but if i connect the plugs together with both the brown and red wires connected and remove the red fuel pump relay and jump terminals 30 and 87a the fuel pump runs and the car starts and also what could be the problem for the battery light being on could the owner have fried the whole alternator it self or what please let me know thanks again appreciate it guys

[Porboynz]

I am going to do my part towards getting this Porsche back on the road by re-writing the post as I read the situation, I am assuming you repaired all the burnt wires you found yes?

Hello again, a customer brought in a 1981 911 couple saying the battery light was on. We asked him what happened and he admitted that when he changed his battery he put the positive on the negative and vice versa. This fried the alternator wire and other wires which we repaired. The battery light was still on and we measured 11.3v, so the boss told us to change the voltage regulator and now we get 13.5V which is better but the battery light is still on.

When the two white connector towards the bottom of the picture next to the black connector are unplugged the fuel pump runs and there is no spark.
With the white connectors plugged in the pump doesn’t run and there is spark.
If I take the brown wire off of the connector on the right side and plug it in the fuel pump runs and we have spark. That ground wire isn't allowing us to have both spark and have the pump running at the same time!

If I connect the plugs together with both the brown and red wires connected and remove the red fuel pump relay and jump terminals 30 and 87a the fuel pump runs and the car starts.
That still leaves us with the problem of the battery light being on, could the owner have fried both the regulator and the diodes in the alternator?
Thanks again and appreciate any help guys

[Porboynz]

The problem with the ground wire is almost certainly a missing ground connection somewhere, or a damaged fuel pump relay. (it works OK when you bypass the relay so suspect the relay) That white plug looks like the connection to the fuel pump and so the brown wire is the main earth for the pump and the red wire goes to the fuel pump relay. Therefore it is surprising the pump runs when its not connected, unless the pump is also earthed through the pump housing. There may be more damaged wiring to discover, plus usually at least one alternator diode shorts out when you reverse the battery connections and that would explain the 13.5V and the warning lamp. Good luck, maybe a multi meter can help isolate the fuel pump problem and check where that earth wire goes.

[T77911S]

the engine has to be running, starting or the connector on the rear of the AFM has to be removed for the pump to run.
it will NOT run in the ON position unless the connector on the AFM is removed.

[T77911S]

one of the connectors has power to the CD and the ground to from the FP relay to the AFM SW. with that one unplugged, the FP will run (key on engine off) but you have no spark.

sounds like it is working like it should