Power Problem
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New User
Joined: Feb 2017
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Power Problem
1987 ford f350 6.9 idi i have two new batt. and I changed the wires to the truck charged up batteries truck started batt. light was on had head lights and before i also changed the solenoid and few months ago i changed that little grey box for power can't think of the name. batt needle was low but it started up had head light and power drove and ran the truck 45+ mins before i shut it down went to try and re start the engine not enf. power to start ?? allt. belts where changed and tighten up starter seems to work well once i charge up batt. any idea's what it might be thank you
Mountain Pass
Joined: Sep 2015
Posts: 178
Likes: 3
If the truck starts and runs effectively once you charge the batteries, the alternator has to be the problem. Here are some methods for testing the alternator to ensure that you are not wasting money. Also alternator problems do not necessarily have to be the alternator it's self. It can be the wires going to and from it. Also a fuse I believe on your truck.
First, get a cheap volt meter from any store. They are like $12 for a decent one. Check the voltage on the batteries with the truck off. Should be around 12.7 to a low of 12.2 ish... Next start the truck, and then check the voltage. It should with the truck running be between 13.9 to say 14.7. This would indicate that the batteries are indeed charging. If it is still the 12.7 or (engine off voltage) then the alternator is not supplying power to the batteries. At that point you could start trying to further diagnose the problem, or take the alternator off and have it tested at a local auto parts store. I believe all of them test them free now.
Best of luck, if you need help with further diagnosis please update.
First, get a cheap volt meter from any store. They are like $12 for a decent one. Check the voltage on the batteries with the truck off. Should be around 12.7 to a low of 12.2 ish... Next start the truck, and then check the voltage. It should with the truck running be between 13.9 to say 14.7. This would indicate that the batteries are indeed charging. If it is still the 12.7 or (engine off voltage) then the alternator is not supplying power to the batteries. At that point you could start trying to further diagnose the problem, or take the alternator off and have it tested at a local auto parts store. I believe all of them test them free now.
Best of luck, if you need help with further diagnosis please update.
Elder User
Joined: May 2018
Posts: 695
Likes: 22
A quick check. Unplug the terminal at the regulator. Jump battery voltage directly to the field terminal at the alternator which forces the alternator to put out its maximum voltage. Then check that voltage. Should be 14-16 volts if alt is OK. Matter of fact, if done on a gas engine you can hear the engine bog down slightly as you energize the field terminal.
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