Power only comes on intermittently

[melueloff]

I’ve been through most everything I can find on this problem, but mine seems to have a twist no one else has reported. Beast has run just fine off and on over about the last five years I’ve used him until now. Has been in pretty much constant service for the last two years. Sorry, it’s kinda long but I’m trying to be thorough.

About three weeks ago we went up into the mountains to put our trailer in storage for the winter. Did just fine until I dropped the trailer, pulled forward and turned him off. Went to start up again and it wouldn’t do anything. Power went out on the dash, little puff of electrical smoke up from the drivers engine side of the firewall somewhere. Tried the only thing I knew and tapped on the starter. Yes I know you’re not supposed to do that. Another time or two trying to start nothing happening and another puff or two of electrical smoke up on the drivers engine side of the firewall again, more tapping and he fired right up. Got back down into town, he worked for another two or three days and did it again. Tapped on the starter, he would start. Now, nothing. I turn the key, get the CEL and seatbelt light sometimes. Turn the key, dead. I pulled the starter and benched tested it, it’s fine. The battery just sitting is reading 12.3 V. I tried jumping the neg battery to a spot on the alternator to ground, nothing. I’ve checked the fuse links, they’re good. I’ve replaced the ignition module and that hasn’t helped. And I’ve put hands on every inch of wire I can.

But now, I found something different from everybody else. Turning the key may or may not light up the CEL and seatbelt light, but when it does there’s a relay click under the dash. It’s not outside in the engine compartment and it’s not the starter solenoid, but I can’t figure out what it is or where it is. I’ve been trying to find if there’s a relay that could be bad but I read electrical diagrams about as well as I read Greek. And the dash lights will come on, with the relay click on their own and go off on their own.

Laugh, point, laugh And point. It’s all good lol

 

[75gmck25]

Your truck is much newer than mine, but in my truck it would be the fusible link that comes straight down from the power junction next to the brake booster. This 10 gauge wire with 14 gauge fusible link is what powers the dash and the HEI. If it has too much current it will start to burn through inside (the puff of smoke), but may keep enough integrity to power the dash. Usually it only takes a couple of “incidents” to burn through completely.

My fusible link started to fry/smoke when I installed battery cables backwards, but then worked fine later on. I didn’t realize how much it been weakened. Later on I was driving on the highway and turned on the headlights. The extra power draw and the extra amps burned completely through the link and I suddenly came to a stop on the highway. I spliced it temporarily, and then later replaced the link with a 14 gauge GM fusible link I bought at the parts store.

 

[melueloff]

75gmck25, I’ll go back and check those out again. I did continuity but not voltage. Maybe I’ll just replace all three of them to be on the safe side.

 

[melueloff]

We’ll, hours later, busted knuckles, more swearing than a battalion of Marines, and a sunburned leg, I went back to square one. Burnt out fusible. I had cut into it above where the wire itself had blown out. Replaced it more or less correctly and darn thing fired right up. Occam's Razor, “the simplest solution is almost always the best.” LOL

 

[Scott91370]

Is there not a "real fix" to these fusable links that won't burn the truck to the ground?

I've been lucky and haven't had any issues (I should not have said that!!!) but so many do. And from what I understand you can't just put a regular fuse in its place.

 

[YakkoWarner]

Is there not a "real fix" to these fusable links that won't burn the truck to the ground?

I've been lucky and haven't had any issues (I should not have said that!!!) but so many do. And from what I understand you can't just put a regular fuse in its place.

I don't know - but I would love to understand the reasoning about why just using an inline fuse won't work (seems like the concept is the same, too much current and it pops protecting from fire).

 

[Snoots]

Just an FYI:

Understanding Fusible Links ~ The One Wire That Will Save Your Car!

In an extreme current overload situation, a fusible link is melted, and ensuing spark and fire are contained within the link's insulation...

m.roadkillcustoms.com

 

[Ricko1966]

I don't know - but I would love to understand the reasoning about why just using an inline fuse won't work (seems like the concept is the same, too much current and it pops protecting from fire).

The surge current on a fusible link is completely different. Theses are not real numbers just examples,all fusible links would not have the same values. But let's say you had a fusible link that would take a 50 amp surge but burn with 30 amps continuous, you would have to replace it with a 50 amp fuse to keep it from popping,but a 50 amp fuse would be too much to protect the circuit over an extended period.

 

[Ricko1966]

Is there not a "real fix" to these fusable links that won't burn the truck to the ground?

I've been lucky and haven't had any issues (I should not have said that!!!) but so many do. And from what I understand you can't just put a regular fuse in its place.

A fusible link won't burn your car to the ground. Replacing one with plain wire or a fuse might though.

 

[Jgonick]

i always liked this explanation-

"Fuses blow relatively faster than fusible links, providing quicker protection to the electrical system. Fusible links, on the other hand, are more tolerant of short-duration faults and can withstand higher current surges for a short period of time."

 

[YakkoWarner]

i always liked this explanation-

"Fuses blow relatively faster than fusible links, providing quicker protection to the electrical system. Fusible links, on the other hand, are more tolerant of short-duration faults and can withstand higher current surges for a short period of time."

OK that actually is an explaination that I can comprehend the concept of. With all the other electrical gremlins I've encountered in my truck, I would not be surprised to find some of the links bypassed or removed. Do any of the manuals have a comprehensive list of which circuits have fusible links, and even more importantly WHERE they are (or should be) located)??

 

[Jgonick]

Do any of the manuals have a comprehensive list of which circuits have fusible links, and even more importantly WHERE they are (or should be) located)

Wiring diagram LINK

Attached is an example for 89 & 84 "Fusible link" - usually on starter, junction block -alternator

In example- wire size is metric- 84 the first number is wire size & 89 it is the second number.

Also attached is other helpful info.

 

[Scott91370]

I don't know - but I would love to understand the reasoning about why just using an inline fuse won't work (seems like the concept is the same, too much current and it pops protecting from fire).

A fusible link won't burn your car to the ground. Replacing one with plain wire or a fuse might though.

I get that @Ricko1966 but as mentioned above by YakkoWarner, why? You may or may not know - I definitely don't and won't pretend to.

As he says, I (we) would love to understand why it won't work and why it was designed the way it was. You have to admit it's annoying to have wiring protected by thinner wiring that isn't as easy to replace as a fuse if something goes wrong.

But if the explanation that Jgonick gave is true then why would a fuse burn the truck to the ground?
[insert thoroughly confused emoji here]

 

[Ricko1966]

I get that @Ricko1966 but as mentioned above by YakkoWarner, why? You may or may not know - I definitely don't and won't pretend to.

As he says, I (we) would love to understand why it won't work and why it was designed the way it was. You have to admit it's annoying to have wiring protected by thinner wiring that isn't as easy to replace as a fuse if something goes wrong.

But if the explanation that Jgonick gave is true then why would a fuse burn the truck to the ground?
[insert thoroughly confused emoji here]

Okay the reason a fuse might or a piece of plain wire might. A fusible link will take a surge of say 50 amps and not blow but will blow pulling a continuous 30amps through it. So if you wanted to replace the fusible link with a fuse you would have to use a 50 amp fuse to accommodate for the sirge rating,but 50 amps is too high for continuous as all the other wires will overheat. The fuse doesn't have the capability of a high surge rate and a lower continuous rate to pop. A fuseable link ,the jacket is fire resistant its not just regular wire,so when it burns it won't set your car on fire. When your 16 gauge wires in your dash overheat and burn because you have a 50 amp fuse instead of a 30 amp fusible link,the dash wires are not in a fireproof jacket. So now you get fire.

 

[Snoots]

Welp, OP bailed 10 months ago. Point is, DORMAN makes fusible links so, unless you just have an insatiable urge to melt/fry your harness, there ya go.