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I have a 1970 Mercury Cougar with a 351 Cleveland. A few weeks ago I started noticing the engine would occasionaly cut out while driving and occasionaly I couldn't start the car without wiggling the original double ground cable which was extremely corroded. As a result, I ordered a new cable and installed it last week. My problem is that I'm still having the same problems. I'll be driving along and the alternator light will flash on and off in cordination with the engine cutting out. Additionally I still have to occasionally wiggle the ground cable to start the engine as well. The double ground cable is a single cable running from the battery post to the back of the alternator and then down to the block. Sorry for the lengthy post but any advice would be appreciated. Is it the cable or is my alternator going out. Thanks.
 

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something isnt tight or is corroded. you say you replaced the cable with a new one, so i doubt theres a break in the cable, but if the post on the back of the alternator or the attachment on the block is loose or corroded, it will give you the same issue. and if you have to wiggle the cable, that makes it obvious something with that portion of the circuit is messed up...and im betting its a connection thats loose or pulled away from wherever its supposed to be fastened...
 

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...The double ground cable is a single cable running from the battery post to the back of the alternator and then down to the block...
I could be wrong, but this does not sound stock to me. There should be a cable that runs from the firewall to the back of the PS head, at least on 69. Not sure if 70 was different but the battery-alternator-block does not sound right (and notice what's missing - the body). Can anyone else comment?

Regards,

Bob
 

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On a 70 the ground cable has a terminal made onto the cable that is grounded to the body at the V/R, and then grounded to the block below the alt., if the alt is grounded, it's through the harness.
 

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On a 70 the ground cable has a terminal made onto the cable that is grounded to the body at the V/R, and then grounded to the block below the alt., if the alt is grounded, it's through the harness.
Correct. It's important to make sure the voltage regulator connection (V/R) is very clean underneath as well. I actually use a bolt to clamp the cable through the inner fender instead of the sheet metal screw.

Alt gets grounded to the block..block gets grounded to the battery.

This little bit of difference in grounding and making sure my alt & v/r were in top working order solved all the electrical inconsistencies I had.
 

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On a 70 the ground cable has a terminal made onto the cable that is grounded to the body at the V/R, and then grounded to the block below the alt., if the alt is grounded, it's through the harness.
This is the correct way for the 70 ground cable to run. I'm not sure the way cougarfann1's is would give the problem he is having though.
 

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I know on my 71 cougar, the ground cable was like this. The mid point of the cable was grounded down below on the passenger side of the block. There was also a ground strap like Bob talked about from the fire wall to the passenger side head or there in that area. The fact that you can wiggle anything means it is still not fastened down tight. If it is the mid point on the cable and you are able to still move it, put a washer on it, the bolt may be a little long and bottoming out in the hole for the ground.
 

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So "fann" should be looking to see what he's got going from the battery negative to the body, if nothing this should be corrected and is likely the cause of the problem
 
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