Weak charge

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Weak charge

Post by beanmf »

Car was not used much then stopped starting; stored outside. 1-year old battery in place and on a smart tender but no longer shows "charged". Replaced ground cable. Tried jump starting. Replaced ground wire clamp to battery. I sometimes get a light or weak evidence of connection, but not enough to turn the engine over. Ground wire to frame bolt shows some resistance (needle mid gauge). Before I take the ground harness apart and replace the somewhat new battery, does anyone have experience with weak points that might lead to this? I tried searching on "not charging" but am not clear how to search on combined wordings like that.


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Re: Weak charge

Post by jimi »

I'd be suspicious of the battery. Try disconnecting the battery and charge it with a proper charger for at least 8 hours, then see what the voltage is on the battery.
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Re: Weak charge

Post by beanmf »

It should read 14 V, fully charged, right? I did that charge, but will repeat. Good separation of concerns.
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Re: Weak charge

Post by jimi »

Won't be as much as that, anything around 13v should be ok, but not a guarantee, even a battery with a duff cell can show a good voltage until you put it under load, then it will drop like a stone.
Are your battery clamps good and tight when on the battery ? No corrosion on the inside ?
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Re: Weak charge

Post by beanmf »

Battery charged for 48 hrs, reads 13.5 V. Posts are clean; - cable is new; + clamp is new (last thing I did, months ago). Continuity tested from ground to car body and + to fuse block. Jumper cables to a second car which is running. On MR2, no interior dash lights, no fan, no radio, no window motor, but headlights lift up and down easily. Still no noise or clicks from starter, so I'm wondering if a fuse might be blown (perhaps someone jump started this with poles reversed?). If it was just a bad battery, I feel sure we'd at least get some dim dash lights or seatbelt warning sound. Mice could also be a culprit; the car was outdoors the last few winters.

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Re: Weak charge

Post by BYRNEY1984 »

Have you checked the fuse link on the battery positive cable. If this has blown or corroded away you will lose everything.

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Re: Weak charge

Post by beanmf »

No, but will do. However, the headlights move up and down willingly
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Re: Weak charge

Post by jimi »

If the headlights go up/down then the fusible link is ok, everything bar the starter power goes through the link. It does sound a bit like a fuse, you might need to start at the battery and follow the voltage, see where it isn't when it should be
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Re: Weak charge

Post by beanmf »

yes, agreed. I'll have to hunt down some electric schematics and hunger for a digital KVM rather than the cheapo analog I have. Fortunately, I've A/C in the garage as it's rather hot out. One car must move outside though. Many thanks jimi. I've never been to Glenrothes, but rather enjoyed our times at Anstruther.

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Re: Weak charge

Post by beanmf »

Help! jimi posted a link to the MR2 electric schematics on this thread but now it's gone. Can anyone put the link back here for me please? Thank you.
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Re: Weak charge

Post by jimi »

We lost a couple of posts with a technical problem, mine must have been one of them.
Electrical diagrams are in the downloads section https://mr2oc.co.uk/downloads/technical-stuff/mk2.html If you can't find relevant diagrams there then check this thread https://mr2oc.co.uk/forum/topic/worksho ... 80372.html and if you still can't find the right ones PM me and I'll have a look through my files :th:
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Re: Weak charge

Post by beanmf »

Progress. The car now starts and runs. 4 fuses blown (probably by switched poles on jump-starting): AM2, EFI, and dome.
All other fuses in front, rear and driver's side all checked OK.
NOT working: A/C, antenna, p. steering, door locks. Battery light on dash bottom left is let. More work still, but at least I could get it to a shop if needed. The schematics did help (especially focusing on the AM2 fuse in front, so thanks!
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Re: Weak charge

Post by jimi »

Well done and thanks for the update :th:
Connecting the jump leads in the wrong polarity will definitely blow fuses, can also damage wiring.
I spent 2/3 days on a friends MK2 tracing and repairing damaged wiring after a similar mishap, ended up removing the complete dashboard to get to the damaged section. It ran across the car from the junction box in the passenger footwell to the drivers side, 3 or 4 wires had been melted together, can't remember offhand what circuits were affected, but fuses were repeatedly blowing. I couldn't have done it without the diagrams, hopefully yours won't be as bad.
The actual cause of his problems was the battery, he had removed it to put on charge and had somehow managed to charge it in reverse causing the battery polarity to reverse !!! :shocked:
The only time in my 50:years as an electrician that I've come across that.
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beanmf
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Re: Weak charge

Post by beanmf »

omg. That sounds like a gigantic pain in all parts of the body. However, I suspect you are right. Most of the components that don't work are on p. 22 which is "Instrument Panel Parts". Deeper and deeper.
I found the root cause. I replaced the battery a year ago with one where the + and - were reversed from our needs, so I turned the battery around, hiding the +/- symbols. When I hooked it up my smart battery tender I had the quick connect leads backwards; no harm but didn't charge the battery. Later I tried jump starting it (again probably backwards) and --> BINGO.
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