1991 560SEL; starter turns engine but engine will not start!

[qualified-merc]

OK, I was having problems with battery discharging. There are three strange red electrical cables connected to the positive post of the battery. I disconnected all three leaving only the main red battery cable connected.

After I disconnected the three strange/weird red electrical cables, I left the battery on the charger for a few days to bring it to full charge. Yesterday, I tried starting the car. The starter engages and spins the engine at a good rate of speed. However, the engine will NOT start!!

It appears that these three strange/weird electric wires must be connected to the positive post of the battery before the car will start! What?

Photos attached; To be best of my ability I tracked the two red wires down the right fender well (photos). I checked the back of the alternator; it does not appear these red electric wires travel to the back of the alternator. The main cable breaks off and heads downward toward the lower right side of the engine....weird.

It looks like I will need to climb under the car and try and find the exact spot where this main branch of the cable connects to the right side of the engine. Any other ideas? I have never seen anything like this problem;

I am thinking the former owner did some custom wiring for some reason.....

[qualified-merc]

I have not tried to track the third strange/weird wire. I have it coiled up and tied off next to the right fender.

[porkface]

if this is where your fuel pump relay is, look for a red 10 ga wire from it's connector. that will have an eyelet that belongs on the + post.

it's the relay that has 8zyl on it.

[qualified-merc]

OK, after connecting the two wires, the engine did start. I believe I located the fuel relay (photo attached). I put the charger back on the battery.


This may be a situation where I need to keep the car on a battery charger. Still, it makes no sense that when I take the charger off the battery two things happen: A. the battery loses charge and B: the battery itself dies a fairly quick death. So far, I have gone through two brand new AGM batteries, this is the third and it is less than two weeks old.

[porkface]

https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-find-parasitic-battery-drain-with-a-multimeter

[qualified-merc]

thank you for this link; after I mow the lawn in the morning, I am going to do the testing.....