520xi Electrical Short when Key turned to start position

[TedHallCT 0]

I have a 1998 520xi. with about 680hours.   I have recently encountered an intermittent issue when trying to start the engine the entire electrical systems goes dead. All dash lights go off and no headlights. If I disconnect the ground side of the battery and reconnect no change. If I disconnect the positive side of the battery and reconnect everything returns to normal and I can usually start the engine. The first time this happened about a month ago, I bought a new battery. So I know the battery is good. On the most recent event, the new battery was dead. So I did recharge it and I believe the battery was drained while the key as in the off position.  My investigation so far has yielded the above results. On this last event I did check to see if the battery was being drained while the key as in the off position but no amperage evident with an ammeter installed inline with the positive side of the battery. Looking for advice on what to check next. I was wondering if the starter or solenoid could have an intermittent issue also.

 

Ted

[gwest_ca-(File Mod) 11,561]

Have not put this file together yet but will. A preview of this

 

[squonk 44,036]

What scale is your ammeter set at? Needs to be on milliamps.

[953 nut 60,700]

An amp meter may not show a small parasitic draw caused by corrosion and/or a poor connection. Place a 12 volt test light between the battery terminal and the battery cable. May need to turn off the lights to detect the glow of the lamp on low amperage. Do a systematic check of the wiring by wiggling each wire and connector while observing changes in light intensity. Pull and insert relays too because each relay holder has a ground wire going to it. Also, look for potentially pinched wires.

Carefully inspect your electrical connectors for corrosion. Many of the multi wire connectors have a black (ground) wire and a hot wire in them.

[Pullstart 67,244]

What kind of shape is your ignition switch in?  I recently had to replace mine due to abuse and it sort of acted like a wiring issue.  It’s worth checking that with a volt meter / continuity setting.

[TedHallCT 0]

During my investigation I removed the switch. Looked in good condition but needed to be cleaned around the terminals due to a dust and oily build up. I checked the switch terminals for continuity based on the key position and the manual wiring diagram. All looked ok. I cannot rule out an intermittent issue with the switch, but I am not sure if could create a dead short. 

While the battery was connected and the dash was totally dead, I systematically  pulled each breaker to see if any one of them would eliminate the condition. This did not produce any changes. 

I pulled all 3 relays and check with meter, all were ok. Also all connections were clean. 

 

The amp meter was probably set too high as it could read the lights at 5 amps.  I will try the light bulb or risk a lower setting on the amp meter. 

 

Since this is an intermittent issue, my next plan is to isolate the starter cable and remove it when this happens again. This would at least remove the starter from the list of possible causes. 

[gwest_ca-(File Mod) 11,561]

Which fuse are you blowing when turned to START?

To get to START you pass the lights, ignition and rectifier circuits which have fuses and if they are not blowing the problem is most likely in the starter circuit.

 

Garry

[TedHallCT 0]

No there are no fuses blown.  All are good. So focus the should be with the starter circuit.

[gwest_ca-(File Mod) 11,561]

The + battery cable would be my first thought. Don't rule out a bad connection between the actual cable and the terminals at the ends of it.

 

Garry

[squonk 44,036]

8 hours ago, pullstart said:

What kind of shape is your ignition switch in?  I recently had to replace mine due to abuse and it sort of acted like a wiring issue.  It’s worth checking that with a volt meter / continuity setting.

That same scenario sent @rjg854 down a path of "Oh Wow, I got another tractor!"  

[cafoose 3,460]

I've seen battery cables with corrosion all along the cable under the insulation

[Pullstart 67,244]

Possibly you could check voltage + to battery ground post following connections, looking for a visible drop too.  These are great “fun” to troubleshoot, unless they are NEEDED ASAP!  

[TedHallCT 0]

Interesting picture with the corrosion on the main line between the battery and starter solenoid. Since the switch gets power from the connection at the start solenoid, I have moved that wire to the battery.  This will allow me to isolate the start system.  

 

For now I am just waiting for the next time this condition occurs. Since this is an intermittent problem, it may be some time before I get back to you.