[solved] LH2.4 battery drain issue

wzrdovryndr

Evening all,

I have a ‘91 240 B230F LH2.4 that’s been sitting for a while, which I’ve been “restoring”.

It hasn’t had a battery for at least a year, and now I’m ready to take it for a roadworthy I popped a new one in and hooked up the terminals - locked it up, didn’t drive it.

Next morning, battery was DEAD flat.

Disconnected all fuses to work out where my fault is, found I have continuity to ground on the solid blue ignition wire between the ignition coil and the hot side of fuse 5#.

It still starts and runs, so I don’t believe it’s an ignition switch issue. I don’t have continuity to earth at fuse #6 solid red either.

All fuses for central locking, lamps, etc have been pulled.

Measured 0.7ohm draw on the battery between negative battery terminal and negative post on battery.

carnut222

Do you have the wiring diagram? If not, I might have it somewhere as a PDF.

When you say you have continuity between the blue coil wire and ground, could it just be that you're measuring the resistance between the + and - wires on the coil or something? If you disconnect the red/white wire off the other side of the ignition coil, are you still seeing continuity to ground on the blue wire? What happens if you disconnect the coil lead that goes from the coil to the distributor. Any change? Maybe I'm confused about the resistance between terminals on the coil...

wzrdovryndr

carnut222
Do you have the wiring diagram? If not, I might have it somewhere as a PDF.
When you say you have continuity between the blue coil wire and ground, could it just be that you're measuring the resistance between the + and - wires on the coil or something? If you disconnect the red/white wire off the other side of the ignition coil, are you still seeing continuity to ground on the blue wire? What happens if you disconnect the coil lead that goes from the coil to the distributor. Any change? Maybe I'm confused about the resistance between terminals on the coil...

I have the wiring diagrams, and I think I’ve narrowed down where my suspected issue is. See the highlighted wires:

With the fuse removed, I checked continuity between earth and the input side of fuse #5. With the blue wire plug disconnected from the coil, I also checked continuity from the plug to to earth. Both indicated continuity to earth and from what I can find that wire should not be grounded with ignition on or off.

carnut222

Strange...does the speedometer work?

What's the "diagnostic connector" that's also a blue wire - IIRC there was one down by the coil somewhere.

You'd think if it were a short to ground, it would blow a fuse. So not sure what else could cause a slow current draw.

wzrdovryndr

carnut222
Strange...does the speedometer work?
What's the "diagnostic connector" that's also a blue wire - IIRC there was one down by the coil somewhere.
You'd think if it were a short to ground, it would blow a fuse. So not sure what else could cause a slow current draw.

Haven’t looked into speedo yet. The speedo used to work, but haven’t driven it for 2 years, but this issue wasn’t present back when it was parked up.

Diagnostic connector is a little black box on the left hand strut tower, it’s a little light bulb that blinks. I’ve used this to check ECU and EZK function and all checks out. I’ll follow the wiring back to that and see if there’s a wire that’s rubbed through.

jamesinc

If you look at that ignition switch in the diagram, you can see that when the car is off (or in the key I position), that fuse #5 is isolated from battery positive by the ignition barrel.

So, if you want to know for sure if the problem circuit is on fuse #5, with the car off, check the voltage drop to ground on both sides of fuse #5. If you see 12V on the ignition switch side, the problem is probably the ignition switch. If you see 12V on the fused side, the problem is some other circuit has bridged onto this one and is powering it. If you don't see voltage on either side, then you can rule this circuit out.

You would always expect to see continuity to ground because fuse #5 is always connected to ground, via the speedo and coil (and other devices), but it should not be a short circuit.

wzrdovryndr

A friend of mine showed me how to properly diagnose the issue, I was obviously following what I thought were issue but, as @jamesinc said, fuse #5 is grounded.

With the key off I had a 3 amp drain on the battery which would disappear if I pulled fuse #6. We traced the issue back to the plug I spliced in to my dash loom to connect to the ‘93 engine loom. Found the wire with high draw and unpinned it and the draw dropped to nearly nothing.

Engine starts and runs with that power wire disconnected and all dash lights work.

I still need to trace the wire and find what was causing the drain, but I can leave my battery connected now!