1985 500sel gray market. The car is having problems keeping battery charged
as we don't drive it very often anymore. but everytime that I have to charge
battery, the security ssytem must be disabling the fuel pump. I figured this
out by checking current at fuel pump. I was able to lock/unlock doors from
trunk with the key to reset security system and it would work again. However
the last couple of times that has not worked. I bypassed a wire directly
from battery to fuel pump to start the car, somehow by doing this it reset
the system to a state where it would work again. No w a week later it has
happened again. I was able to again use the wire from battery to fuel pump
to start and after a few times of starting engine, the system reset itself.
I would like to just get rid of this 'security' feature, I don't believe
anyone is going to steal my 1985 car that has 160k on it anyway. Is there
anyway to straight wire the fuel pump past the security system?? The way I
have been doing it causes pump to run all time instead of intemittently. I
found a "fuel control unit" under the passenger floor mat with many
aftermarket wires pulled to it. I have traced most of them and can post
picture if needed. Two of them go to intake manifold to some type of sensor
that buzzes. There is two power wires. three grounds. any ideas?? None of
the aftermarket wires go to the fule pump. It doesn't even seem that the
fuel control unit is even doing anything.

I have an '86 420 sel that had an alerm issue that caused teh alarm to
go off while driving (fun). I solved this by disconnecting the factory
alarm. There are two connections that need to be removed under teh
passenger floor mat. A quick google should point out the correct ones
to pull. I would think it would address your issue as well.

I don't know about the 85 500SEL EURO but on my 84 500SEL US car, the fuel
computer in in the right kick panel and the unit under the plastic panel on
the right side floorboard is the alarm system. You should be able to
disconnect but the automatic trunk lock will not work. I think the door
locks will still work. I had your exact problem of the fuel pump not
starting and it was the fuel pump relay. I would take it out, jump the fuel
pump, get the car home, reinstall the fuel pump relay and all was well until
the next time it happened. It was a bad solder joint in the relay.
Resoldered and every thing has been fine. That was about 5 years ago. Next
time it happens, just tap on and move around the fuel pump relay and see if
it will start. If it does, fix or repair the relay.

"jb" <mjburks (AT) alltel (DOT) net_nospam> wrote