Electrical Questions
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Junior User
Joined: May 2004
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From: Tucson
Electrical Questions
A while back I installed a ProForm HEI ignition into my 78 F-150/460/Supercab. I connected the single positive power wire to the factory wire leading to the factory ignition module.
It works fine, with the exception of not being fully plugged in the other day and giving no spark
I was going through the fuses in the cab to make sure they are all fine and correctly sized (amperage). I figured I had better look into this before it becomes a problem. Knock on wood no fuses have blown ever and all the electircal seems fine. I was initially concerned because like 1/2 of the fuses ever manufactured were (spares?) inside of the glovebox when I bought thte truck.
1. During this process of inspecting the fuses, I wanted to see what fuse the ignition actually draws power through. To my suprise, the truck starts and runs with no fuses. After reading in a Hayne's manual it looks like the ignition system uses a fusible link rather than fuses. Is this correct?
2. One of the fuses mentions the engine and is switched by the key. What does this go to?
3. What is the emergency fuse that has yellow inside of it? It is rated for 20 amps I believe but does it take longer to burn etc?
4. I never knew there were so many [physical] sizes of fuses. Do all the trucks of this generation have so many different lenght fuses? Anyone have an idea of why there are so many sizes?
It works fine, with the exception of not being fully plugged in the other day and giving no spark
I was going through the fuses in the cab to make sure they are all fine and correctly sized (amperage). I figured I had better look into this before it becomes a problem. Knock on wood no fuses have blown ever and all the electircal seems fine. I was initially concerned because like 1/2 of the fuses ever manufactured were (spares?) inside of the glovebox when I bought thte truck.
1. During this process of inspecting the fuses, I wanted to see what fuse the ignition actually draws power through. To my suprise, the truck starts and runs with no fuses. After reading in a Hayne's manual it looks like the ignition system uses a fusible link rather than fuses. Is this correct?
2. One of the fuses mentions the engine and is switched by the key. What does this go to?
3. What is the emergency fuse that has yellow inside of it? It is rated for 20 amps I believe but does it take longer to burn etc?
4. I never knew there were so many [physical] sizes of fuses. Do all the trucks of this generation have so many different lenght fuses? Anyone have an idea of why there are so many sizes?
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Joined: Dec 2001
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From: Louisville,Ky.
1. Yes it uses a fusable link.
2. Throttle solenoid and emission control circuitry.
3. That sounds like a slow blow fuse. My 77 owners manual says that is is 20amp code yellow.
4. Yes they have 4 or 5 different sizes!! Must be why there were so many spares, so there would be some for each size.
2. Throttle solenoid and emission control circuitry.
3. That sounds like a slow blow fuse. My 77 owners manual says that is is 20amp code yellow.
4. Yes they have 4 or 5 different sizes!! Must be why there were so many spares, so there would be some for each size.
Posting Legend
Joined: Sep 2001
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The different physical sizes were originally intended to prevent interoperability between fuse types, -didn't work out tho. There were many types of fuses with different time vs current blowing characteristics. With the introduction of the blade type fuses and fusible links things seemed to get simpler for a while. However nowadays all you have to do is check out the local auto parts store to see a whole array of fuse types.
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Junior User
Joined: May 2004
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From: Tucson
Fusible Link location...
Where are the fusible links generally located for the 12v+ power to the stock coil and ignition module?
Hopefully (under the dash)...
I just want to make sure there's a fusible link going to my HEI distrib..
Hopefully (under the dash)...
I just want to make sure there's a fusible link going to my HEI distrib..
Lead Driver
Joined: Nov 2000
Posts: 6,637
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From: Albuquerque
On a related note:
The factory ignition power supply has a resistor wire in it to limit current. Voltge running will show about 7 to 9. The H.E.I. needs 12v to function efficiently. I use the factory wire to trigger a relay that feeds my ignition and fuel pump 12v through a large gauge wire. I used an in line fuse but don't remember the amperage. Probably 20a.
The factory ignition power supply has a resistor wire in it to limit current. Voltge running will show about 7 to 9. The H.E.I. needs 12v to function efficiently. I use the factory wire to trigger a relay that feeds my ignition and fuel pump 12v through a large gauge wire. I used an in line fuse but don't remember the amperage. Probably 20a.
