3G alternator swap problem
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Not really. Ford used really small wire and there is a significant voltage drop inside the cab. That's why I asked your only reliable way to find out if the alternator is working right is to test at the solenoid. If that is good and you want to chase the voltage drop to the inside of the cab then proceed from there. But one thing at a time.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Further to that, there are known voltage drops in these trucks when the connections are perfect, meaning new. The headlight switch and associated wiring, and the ignition switch and associated wiring. Both are known to show a significant voltage drop when the headlights and fan are on full. And then there is the cab ground, which is frequently left off when engine work is done. For all of those reasons you must check the alternator's output voltage at the solenoid, not inside.
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The yellow wire goes into the cab. Some of the trucks had two yellow wires, one goes to the ignition switch and ones goes to the fuse box. But some only had 1 wire, and there is a splice under the dash where it splits and goes to the ignition switch and the fuse box.
What I would do is get everything going with the fan on high, and take a measurement at the fuse box. If it's low, then you know the problem is with the yellow wire somewhere.
But, I am with some of the others in this thread, I bet you do not have a problem, it's just the way it is on these trucks. If you want to beef up the wiring go ahead. But you are not going to be able to shove 200 amps into the original truck's wiring. Most people who buy these large alternators buy them for some other reason, and add little aux fuse boxes under the hood to distribute the power to their added power hogs, and leave the stock wiring alone.
You will never be able to realize the full output of this 200 amp alternator anyway of you are only running the stock single groove v-belt. It's a little thing that the people that sell these alternators just happen not to tell you about.
What I would do is get everything going with the fan on high, and take a measurement at the fuse box. If it's low, then you know the problem is with the yellow wire somewhere.
But, I am with some of the others in this thread, I bet you do not have a problem, it's just the way it is on these trucks. If you want to beef up the wiring go ahead. But you are not going to be able to shove 200 amps into the original truck's wiring. Most people who buy these large alternators buy them for some other reason, and add little aux fuse boxes under the hood to distribute the power to their added power hogs, and leave the stock wiring alone.
You will never be able to realize the full output of this 200 amp alternator anyway of you are only running the stock single groove v-belt. It's a little thing that the people that sell these alternators just happen not to tell you about.
FTE Legend
Joined: Jul 2010
Posts: 32,875
Likes: 48
From: Northeast, OK
Yep. Testing has shown a single V-belt good for 95 amps, after which it slips. Which is why I plan on running two belts to my 3G alternator.
The two main power hogs on a stock vehicle are the headlights and the HVAC fan. In the resto mod on Dad's truck I will be installing a fuse/relay box like Dave was talking about. And in the box I'll run relays for the headlights and the fan. That way the itty bitty wires and 33 year old switches will only have to source enough current to pull the relays in and the heavy current will be sourced by my new, heavy-duty wiring.
The two main power hogs on a stock vehicle are the headlights and the HVAC fan. In the resto mod on Dad's truck I will be installing a fuse/relay box like Dave was talking about. And in the box I'll run relays for the headlights and the fan. That way the itty bitty wires and 33 year old switches will only have to source enough current to pull the relays in and the heavy current will be sourced by my new, heavy-duty wiring.
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