No acc. power,but truck runs?

[Dale Reed]

Mechanic put a new battery in and replaced a fusible link with a 60A fuse. Starts and runs well but something else is wrong.



When driving the dash voltmeter is less than centered (always was centered for the old battery) and even more interesting the voltage across the new battery measures 11. 96 V when the engine is running and is 12. 17 V after I turn the engine off.

 

[Paychk]

If you click on the underlined text in my first post it will take you to a site that has a fusible link/amp chart.

FSM = factory service manual

wire gauge = diameter of wire or size (in this case it is the size of the link, the size of the wire it protects is usually but not always 4 sizes larger than the link.

The info on fusible link color/size is in the first few pages right before the wiring diagrams try 8w-3

The amp capacity/color size is not listed in the manuals, that is why I posted the link to the other web site.

 

[Paychk]

The reason the gage in the dash is off is, the alternator isn't charging, if it was you would see about 13. 5 - 14. 5 volts at the battery.

 

[Dale Reed]

The 60 Amp fuse blew! Your link says they would.



Mechanic wants to try larger fuses, maybe even fuse the entire rats nest of fusible links none of which look all that healthy.



But I don't think so. Fusible links have the advantage they protect slowly allowing sharp current pulses to pass without blowing the fuse. I am holding out for fixing the one now replaced fusible link with another fusible link (if we can find one) and giving up on regular fuses.



But then again I assume 2nd gens or at least 3rd gens no longer use fusible links replacing them with regular or maybe sloblow? fuses.

 

[Dale Reed]

Electrical Issues - MiniMopar Resources



Circuit Hypalon Link Type MAXI Fuse Rating Circuit Wire

Alternator Feed (R6) 12 gauge (black) 160 amp (2x80 in parallel) 8 gauge (BK)



Since my alternator is not working then the replaced fusible link was probably "black" and designed to protect wiring that carries 160 Amps?



The mechanic says he remembered that the replaced wire was "green. "



The plot thickens!

 

[Dale Reed]

Mechanic found the parts of the fusible link he replaced.

He says

"I found your fuse links fetid remains- it says 10 gauge and its green. "



He ordered a new fusible link and will remove the fuse holder and install a new green fusible link next week.

 

[Dale Reed]

If the 10 gauge green fuselink does not work then Amazon sells high Amp Slo-blo fuses that I bet would.

Amazon.com: Littelfuse MEG100BP MEGA Slo-Blo Automotive Bolt-Down Fuse: Automotive



Must be kept in mind that something melted the insulation off the replaced fuselink so what size Littelfuse should I use to replace the fuselink would you replace it with? I figure that the insulation melted because it is an old truck *and* it was having a difficult time trying to charge the 4 year old Interstate battery.

 

[Dale Reed]

Page 8W-44 of the FSM shows:

"FUSIBLE LINK

(10DG) 50/120 AMP

(LEFT FRONT WHEELHOUSE)"

between the positive terminal of the Battery and the CHARGING SYSTEM.



Apparently the truck requires a Dark Green 10 Gauge fusible link or a 120 Amp slo-blo fuse. But what does the "50" of the 50/120 number mean?

 

[Paychk]

I'm not sure what the "50" means.

Something else you could try are self resetting 12 volt circuit breakers, like what semi-trucks use.

 

[Dale Reed]

Until I learn better I assume that the maximum current out of the alternator is 120 Amps and the idle current is 50 Amps.



So there is no wonder that the mechanics 60 Amp fuse would not handle the charging current from the alternator to the battery.



But why must the fuse must be slow to open? Even if he had installed two 60 Amp fuses in parallel or one 120 Amp normal fuse I assume it might of blown. I guess the current from the alternator to the battery contains spikes that would blow a regular fuse and that is one of the reasons the slow to open fusible links are used in this circuit and maybe the reason it is used at other locations in our trucks.



Paychk, for sure a circuit breaker (or multiple ones) sounds attractive if I had ever had trouble with the fusible links before or if installing the DG 10 Gauge does not fix the truck. I was hoping someone would tell us what is used on the lastest Mighty Cummins trucks.

 

[HHhuntitall]

The 94 up trucks use a large, 120 amp terminal fuse. The alternator wire runs from the alternator to the fuse block, where the fuse jumps between the terminals to the wire running to the battery terminal.



Oriely's part number for an '03..... Littelfuse PAL2120 - PAL Fuse | O'Reilly Auto Parts

 

[Dale Reed]

Thanks HH. These fuses and others like them are also sold by Amazon.



Sooner or later I will probably use one of them to protect the alternator to battery cable for my Mighty Cummins but for now a jury rig of a short piece of orange 10 gauge fusible link wire with terminals is being installed to fit in a large fuse holder near the battery. If it works that will get me going for awhile.



The TDR certainly is a might fine way of determing how to best keep our old trucks running.