Electrical Issue?
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4th Gear
Joined: Sep 2025
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Electrical Issue?
I’ve got a 1986 F-250 with the 7.5L carbureted engine, and I’ve been chasing an electrical issue I can’t seem to nail down. The truck will randomly blow a fuse and die. It’s an inline fuse I installed on the alternator circuit going to the solenoid (it originally had a fusible link, but the wire burnt up so I swapped in a fuse and I’m currently running it with a fuse saver).
Sometimes the truck runs great with no problems at all. Other times, it misfires, pops a lot, or just shuts off completely. I haven’t been able to find a clear pattern to when it happens.
One odd thing I noticed: I had the cluster out recently, and during that time the truck ran fine for about 4 days—only an occasional misfire, but no dying. After those 4 days, the stalling issue came back.
So far, I’ve replaced the cap and rotor, plug wires, ignition switch, solenoid, and starter. Still no luck figuring this out.
Any advice or ideas would be appreciated.
Sometimes the truck runs great with no problems at all. Other times, it misfires, pops a lot, or just shuts off completely. I haven’t been able to find a clear pattern to when it happens.
One odd thing I noticed: I had the cluster out recently, and during that time the truck ran fine for about 4 days—only an occasional misfire, but no dying. After those 4 days, the stalling issue came back.
So far, I’ve replaced the cap and rotor, plug wires, ignition switch, solenoid, and starter. Still no luck figuring this out.
Any advice or ideas would be appreciated.
Cargo Master
Joined: Mar 2008
Posts: 2,561
Likes: 206
From: Washington
How many amps is the fuse, the one you are using instead of the fusable link?
G2 alternator?
Do you have Amp gauge in the instrument cluster? Does the amp gauge go negative when you turn on the headlights or heater fan on high, engine OFF?
Jim
G2 alternator?
Do you have Amp gauge in the instrument cluster? Does the amp gauge go negative when you turn on the headlights or heater fan on high, engine OFF?
Jim
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4th Gear
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The truck does have an amp gauge in the cluster. When I first start it up, the needle will jump up about a quarter, then bounce back and forth a little bit, and then settle.
Cargo Master
Joined: Mar 2008
Posts: 2,561
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From: Washington
The fuse I’m using right now is a 20 amp. I’m not sure what alternator I have, but I believe it's a G1. The headlight circuit is currently disconnected because I thought that was the issue, and I haven't had the climate controls hooked up since I've owned the truck.
The truck does have an amp gauge in the cluster. When I first start it up, the needle will jump up about a quarter, then bounce back and forth a little bit, and then settle.
The truck does have an amp gauge in the cluster. When I first start it up, the needle will jump up about a quarter, then bounce back and forth a little bit, and then settle.
Once the alternator is Online and producing power output, it should stay running even if the fuse blows.
As you really don't have any large loads, mostly just ingition, brake lights.... The alternator should keep it running.
If the alternator drops off line, all power needs would have to go through the 20 amp fuse, as soon as the fuse blows the engine would quit.
Jim
Cargo Master
Joined: Mar 2008
Posts: 2,561
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From: Washington
Quote...
The truck does have an amp gauge in the cluster. When I first start it up, the needle will jump up about a quarter, then bounce back and forth a little bit, and then settle.
After you start the engine, the alternator trys to charge the battery, if the battery draws more than the fuse rating it will blow. And thus the amp meter needle "settle".
The engine continues to run until the alternator fails to provide the needed power.
I use circuit breaker, instead of fuses, so you can see them pop.
Jim
The truck does have an amp gauge in the cluster. When I first start it up, the needle will jump up about a quarter, then bounce back and forth a little bit, and then settle.
After you start the engine, the alternator trys to charge the battery, if the battery draws more than the fuse rating it will blow. And thus the amp meter needle "settle".
The engine continues to run until the alternator fails to provide the needed power.
I use circuit breaker, instead of fuses, so you can see them pop.
Jim
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Lead Driver
Joined: Jun 2013
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From: Tolland, CT
You can get the fuse link from auto parts store. Call around.
The fuse you chose is way too small. Get the correct fuse link.
here's one sample,
https://shop.advanceautoparts.com/p/...xoCowwQAvD_BwE
The fuse you chose is way too small. Get the correct fuse link.
here's one sample,
https://shop.advanceautoparts.com/p/...xoCowwQAvD_BwE
Lead Driver
Joined: Jun 2013
Posts: 5,650
Likes: 1,156
From: Tolland, CT
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Normal fuses are known as "fast blow" where fuse link wire is known as "slow blow".
The load on the link will spike higher than the rated load when something is turned on and then settle to below the rating.
You are now running a fast blow fuse so when the load is turned on it blows the fuse and you then have problems.
I would first pull all grounds and clean them maybe even replace the battery cables so you know they are good as looking at them you cannot tell if bad inside or not.
Neg from battery to motor> motor to frame. Motor> cab fire wall with a 10ga wire.
Bad grounds can cause a lot of strange things.
Dave ----
The load on the link will spike higher than the rated load when something is turned on and then settle to below the rating.
You are now running a fast blow fuse so when the load is turned on it blows the fuse and you then have problems.
I would first pull all grounds and clean them maybe even replace the battery cables so you know they are good as looking at them you cannot tell if bad inside or not.
Neg from battery to motor> motor to frame. Motor> cab fire wall with a 10ga wire.
Bad grounds can cause a lot of strange things.
Dave ----
Moderator
Joined: Jan 2001
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From: Virginia
20 amp is not near big enough. I guess you just picked that value out of the air? Your blower motor for the heater has a 30 amp on it. You will need at least a 60 or 70 amp mega fuse depending on the size of your alternator. Or put the fusible link back in.
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