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I've searched and read all of the replies to "alternator failures" on this site and believe I may have a shorted or cracked ground trace in or behind the dashboard.
Had a un-charged dead battery and only 11~12 volt rating at the battery with engine at 2000rpm. Replaced the alternator 3 times without any luck. Noticed that only the far right 2 lights on the dash was lit with the key at position2. Finally dived under the dashpanel and found the main plug loose. Tighten and everything was fine, all lights at the dash was on. 14 volt reading at battery happily being charged by the alternator.
A few days later, noticed that only the 2 far right lights were on again. Battery not charging again, but the plug was tight. Push around behind the dash area and surprised, everything was good again. Didn't notice anything loose.
Have checked every couple of days and notice that it would fail when cold (2 lights lit), but fine when warm (all lights lit). Anybody had this problem or have any suggestions?
Gary
1991 740 Turbo
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Bad exciter wire connection through the IP: see the FAQ.
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See the 700/900 FAQ under 'Select Link' button on the top right.
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I agree, and it seems to be originating somewhere behind the dash. Directly behind the dash is a silver color box about 1" by 3" by 5" with a bunch of wires terminating at a plug. There is also a 1/2" black color plug into the silver box. That was what was loose the 1st time. But the following times, it was tight.
When it is warm (weather), I turn the key to position 2 and all of the warning lights are lit. Therefore the "exciter wire" can do it's job. When it is cold, only the 2 far right warning lights (sit belt and ???) are lit, equal no exciter, no charge.
This happens without me touching any of the wires behind the dash. What could be the cause? Any ideas?
Gary
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Aside from agreeing with the obvious - that you've got a bad connection, broken wire, or cracked IP board, - I think the silver box you refer to is the ABS computer. In poking around there it seems you disturbed a wire or connection related to the fault, so work back along the harness from there. And did you check the harness where it passes under the front of the block, just behind the harmonic balancer? The later 700 harnesses are generally good, but that's a spot where I've seen them chafe through.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina
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No, didn't check the harness under the block. Will take a look as soon as the rain stops.
Any idea how I can confirm it's the dash before tearing everything out and replacing it?
Thanks,
Gary
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I'd start with the obvious: pull the instrument panel and (with the aid of a wiring diagram that I don't have) find the wire that leads from it to the alternator. Unplug it at the cluster, and at the alternator, and test for continuity through it. Go along the harness moving it around, see if continuity is interrupted - indicating a break in the wiring. Then test for continuity to ground - indicating a short.
One more thing, if I recall my theory correctly (it's been a while though) the +12v supplied to the alternator 'exciter' lead serves both to establish the initial magnetic field, and as a reference signal. That +12v is supplied THROUGH the bulb to the alternator - at least, on my Mercedes it was. As the alternator output rises to meet battery voltage the circuit is no longer grounded so the bulb goes out. Practical upshot is, if the bulb burns out or isn't making proper contact to the board there'll be no +12v to the exciter lead.
Also - make sure the ground wire is connected between the alternator and the block!
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina
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Very odd. I suspect you have a loose connector on the back of the IP itself or a cracked circuit board. The flex board constituting the instrument panel electricals is notorious for cracks. The only fix is a new board, not a hard swap. But first try tightening everything in sight.
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See the 700/900 FAQ under 'Select Link' button on the top right.
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An alternator requires a +12 volt potential flowing through it before the car is started to pre-energize the electromagnetic field, which will then be used to generate the power to recharge the battery once the car is running. This pre-req is accomplished by the Battery Failure light on your dash board (which serves double duty to warn you of when the alternator fails, and also to energize the coils before the car starts). The current needs to flow for only a tiny fraction of a second, which is why you can turn you key in the ignition very quickly past postion 2 (run) to position 3 (start) and still have the alternator energized. (the bulb may not even illuminate, but enough current will pass through it)
Many alternators can self-energize themselves when brought up to a speed of 4,500 to 5,000 RPMs, assuming you have a wiring failure and it did not pre-energize. However I would not advise this as a working solution since reving your car up to 5,000 just after a cold start is not the healthiest thing for your engine.
Charging system failures are VERY common on the '80 through '87 Volvo 240/740/760 vehicles due to the biodegradeable wiring harness insulation that was used during those years. However, the newer vehicles seldom have this problem. For everybody who is reading this post that has an '80-'87 Volvo with a 4-cylinder engine, it would merit checking and/or replacing your Alternator D+ wire (small red wire on back of alternator, not the big one that goes to the battery), and your Oil Pressure Sensor wire as these two are commonly the first to fail. You need only to replace the wire section that runs from the Alternator or pressure sensor to the large square harness connection back at the firewall (or the strut tower on the 740/760 vehicles).
If you are experiencing this failure on a later model car, or you've already replaced this wire section on an early model car, check the integrity of the Battery Failure bulb in the instrument cluster. It may have a poor connection in it's socket, or a poor connection at the junction on the back of the instrument cluster. Also check and clean the D+ connection and the ground tether on the Alternator. If you are having trouble tracing the D+ wire or the Oil Pressure wire, consult the Volvo wiring diagrams for you particular year if needed.
God bless,
Fitz Fitzgerald.
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'87 Blue 240 Wagon, 267k miles.
'88 Black 780, PRV-6, 149k miles.
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