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Discussion Starter #1
When the amp light is on, does that indicate over-charge or under-charge, or either? In other words does the light turn on when the voltage/amp is out of the envelope? Amp light came on after starting and driving the car more in two weeks than it has in ten years. Figured it went out. New alt (original is on the shelf) and the amp light is still on.

Next logical step? Voltage regulator? I don't think I've disturbed any grounds. Ideas? and thanks!
 

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The amp light comes on only if the battery is being discharged and the alt is not charging the circuit. It does not indicate an over charge. The battery current goes thru the light, a 15 ohm resistor, and the voltage regulator to the field. If the alt is not charging the light stays on or the voltage regulator could be bad. I don't know if there is a shop around that might test your alt/ voltage reg system but most shops can.
 

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Depends on the voltage regulator - evidently some of the after market ones will illuminate the dash light for both conditions. I'd start by making sure you have good solid grounds block to body. Then measure your voltage coming off the alt - should be north of 13V. you should have four wires going to the regulator, orange ties to the alt, white/black goes to alt field connection, and a yellow goes to the bat side of the starter relay (via a fusible link), a green/red coming from the ignition switch to turn the regulator on/off. (The yellow one might have a cap tied in for noise supression)
 

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Discussion Starter #4
OK. Voltage at battery when off 12.24. Car running normal, off of the high idle, measured voltage at large black wire from BAT terminal to the forward side of the solenoid and measured the same voltage. My guess is that the new alt is not charging. Is the bat wire the correct place to measure the alt output? Does the charging circuit run through the VR? Had the instrument cluster out to replace burned bulb, checked all grounds and plugs, all is good there. Gonna remove the alt at lunch tomorrow and take it in for test on Thurs. I have checked grounds, alt to engine, engine to frame, all check out. I will let everyone know what the tests say. Pray for easy! Thanks for the help and any other thoughts are more than welcome!!
 

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If your alt checks out then yeah - sounding like the VR
 

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Yes the charging circuit runs trough the VR, and you measured correctly on the alt, since it do not read more than 12.24 on the alt, it is not charging well enough, should read between 13.5 to around 14.4 on the alt and battery when running
 

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Always have newly-purchased alternators and starters tested before you leave the store.
 

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Yeah - I learned that one awhile ago. Had one that was in the most impissible spot to get out - took as a few hours of diggin it out. Put the new one in and I'll be damned if that thing wasn't DOA! That really tweaked my nads.....
 

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Test the vr first and if that is good then most likely the alternator. unplug the plug into the vr and jump the a and f terminals with the car running. if your tester reads higher than the 12.5 , should be 14-14.5 then the vr is bad. next whould be to check the wires to the alt. run your tester to the ground of bat and to the bat terminal on back of alt. should not be more than 1/2 volt difference(should read the same as just testing the battery). if higher then replace that harness. if ok than most likely bad alt.
 

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Discussion Starter #10
Well, I got both the old and new alt into the shop. Both tested good. Now I have a new VR and I won't be putting that in until we get below 95 degrees. Thanks for all of the help! I will let everyone know how the VR installation goes and if that solved the prob.
 

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Discussion Starter #11
Well, I put the new VR on the car with a good alternator and started it.....and no luck. Amp light is still on. Any ideas? Going to recheck dash grounds and all engine compartment grounds again. Back to square one.
 

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Test the vr first and if that is good then most likely the alternator. unplug the plug into the vr and jump the a and f terminals with the car running. if your tester reads higher than the 12.5 , should be 14-14.5 then the vr is bad. next whould be to check the wires to the alt. run your tester to the ground of bat and to the bat terminal on back of alt. should not be more than 1/2 volt difference(should read the same as just testing the battery). if higher then replace that harness. if ok than most likely bad alt.

You need to do these tests ..... not just keep changing parts and getting no where ....
 

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Discussion Starter #14
Well after again cleaning all grounds and contacts put the original equipment back on and no amp light! Tested the output at the bat and it was 16.73! Put the new voltage regulator on measured the ouput voltage back to 12.24 which was just battery!! I was going crazy. Went into house and started laughing. I tested alt output at IDLE....up to 2500 rpms now.. and perfect output at 14.5.

Dont forget to bring the engine off of idle!! Did I mention that I would need a lot of help? Thanks everyone!!
 

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You should get around 14V at IDLE, think till about 13,5V you should be ok, lower than that is bad.

If you are getting readings of 16,73V at idle with the old VR??? that's dangerous, battery might overload that way, and worst case scenario fire/explosion, just saying...
If you only have 12,24V at idle with the new VR, the battery won't charge enough, and if you run your headlights, it will probably drain the battery completly
 
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