In this video I will show you how to use an OEM General Motors resistor fuse in a 5th gen 4Runner to up the charging system voltage to 14.4 volts.

Factory 4Runner batteries only need 13.7 volts to properly charge and that is why we only see that voltage from our 4Runners without modification. When upgrading to an AGM battery this can cause issues as AGM batteries require about 14.4 volts to properly charge and maintain capacity.

The alternator in a 4Runner is capable of that higher voltage but is limited by the voltage regulator as from the factory there is no need for anything more than 13.7 volts. By replacing the standard fuse on the alternator signal wire with a resistor fuse we essentially trick the computer into allowing more voltage through.

There are several aftermarket companies making voltage booster fuses that do the same thing by installing a resistor inline but most of those items are quite expensive. An OEM part from General Motors is available to do the exact same thing. For less than $10 and a few minutes with a file on plastic you can achieve the same overboost charging.

As tested and shown in the video. Factory charging was 13.6 volts at idle and about 13.8 when driving.

After installing the voltage booster fuse the idle charging was between 14.1 and 14.4 volts. When the battery needed a charge it charges at about 14.6 volts.

Overall this mod was a success and provides the necessary charging for my AGM battery.

Some of the links below are Amazon affiliate links that help us continue to make these videos.

General Motors, DIODE, 12135037 =

General Motors, DIODE, 12135037 5-pack =

120 Pieces – EPAuto Assorted Car Truck Mini Blade Fuse Set =

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