Hello,
Truck has been down for some time now and while priming the IP (it was removed) I had some electrical mishap happen.
The two 10awg black with orange tracer wires going into fusible links to the starter relay had melted. This circuit has those two black with orange tracers going to the engine harness connector into the two yellow wires supplying high power to the glow plug relay. From what I was able to read, those fusible links were meant to handle up to about 60 amps, but I couldn’t find anything on what amperage the circuit itself is.
I cut them back and since they were both attached to the same eyelet (separate fusible links though) I put them both on a single 8awg inline maxi fuse. Even with 80 amp fuses it keeps blowing.
Do I need to cut that inline maxi fuse out for a higher gauge wire and higher amperage fuse? The original harness had 2 10awg wires going all the way to the controller so I figured the amperage cannot be that high normally yet 80 amp fuses blow.

 

The glow plugs pull a little over 200 amps if all is well.

 

Replacing fuse able links with fuses won't work and combining circuits even less chance of working. Replace fuse able links with new and that should help. Fuse able links are slow blow so amperage rating between links and fuses is not possible all things equal.

 

200 makes sense. I wanted to replace with fusible links but I could only find fusible link wire, not anything with the thick insulation on it. I could try switching it to a 250 or 300 amp circuit breaker

 

Think all you will find is wire. That is all I have ever seem myself. Usually 2 gauge sizes smaller if I recall correctly. Go to parts store and tell them what you want. It is a special type of wire.

 

Are you sure? I am really asking not being a wisea**.

I thought fusable links were a thing of the past...and, trucks since, say, 2000 don't have them. Just larger-amp fuses and breakers.

Roy

 

Like these:

 

And, these breakers:

 

Do a search on the web and report back what you find.

 

No I'm not sure you can't find an equivalent breaker to do the same job as the fusible link. It will have to have a high enough break point so that it won't blow everytime you use your glow plugs. And if it's high enough to not blow then does it protect the wiring from overload? I have seen a lot of people trying to use fuses in place of the fusible links and having trouble with them blowing. Why not get a replacement fusible link same as stock? I think they are available and probably less $$$ than a breaker.

Educate me on how to properly size a breaker to replace the fusible link.

 

I did see that auto parts stores have fusible link wire itself, still not sure about making a new fusible link without that heavy insulation for the smaller wire.
That circuit has 2 10 gauge wires in parallel, according to modern electrical standards that should only be rated to run 40 amps max. This is where my confusion came in.
A couple years ago my alternator blew and took that fusible link with it. I replaced it with a 100 amp circuit breaker and I haven’t had any issues since then. If you look under the hood of my truck it definitely looks like a tweaker has been hard at work but everything worked.

 

This is from the FSM for a 1990:


"Glow Plug Right Bank 14 Gauge Fuse Link
Glow Plug Left Bank 14 Gauge Fuse Link"
.

 

Those two 10 g. wires match with the 14 g. links.

There are benefits of two 40 amp fuses powering two wires rather than combining the two with one 80 amp fuse. The point is to protect the 10 amp wires running to the two banks.

But, your problem with 80 amp fuse blowing makes me wonder if you have a short-to-ground on one side or another.

 

Roy, the benefit of the fusible link is that they are slow blow. So they can take a load for a period of time and not blow. If there is a short then pretty much any line protection will blow. Now whether or not Ford stopped using them and have replaced them with slow blow breakers I don't know. Beside their slow blow characteristics they are also cheaper than a breaker. So Ford used them for those reasons.

 

The slow-blow feature of links is a commonly-held belief.

"Cheaper" is 100% for sure.

In an earlier post, I asked if modern trucks still use links. It is clear that they do.

To the OP: (1) if both your links blew, I suspect a short-to-ground in the controller, (2) I would troubleshoot the issue and eventually go back to the original two lines going into the controller. Each with either a link or fuse.

If it is the controller, now might be the time to relocate it to a cooler, less vibration, location.

Roy