Tech Tip: Transit 150 Alternator Overcharging

July 12, 2024

A customer brought their 2016 Ford Transit into an auto shop with multiple warning lights on.

Related To: ALLDATA

A clinet brought their 2016 Ford Transit 150 into the shop. The Transit had multiple warning lights on in the instrument cluster, and all the gauge needles would drop to zero as soon as the engine started.

Case details

A quick check of the charging system reveealed that it was charging at 18V. Since he hadn't run across this issue before and was pressed for time, the technician called ALLDATA Tech-Assist for some diagnostic guidance.

The consultant suggested disconnecting the alternator’s 3-wire connector, then starting the engine and revving it up 2-3 times. The alternator should go to a default charge of 13.5V. If it were still at 18V, the alternator would be the issue.

If the charging system did go to the 13.5-volt default charge, then check for power at the alternator red wire (pin 3). If there was no power there, inspect inline fuse #1 at the battery-positive terminal fuse box.

Lastly, the consultant suggested inspecting connectors C139 (near left strut tower) and C1280 (near the left headlamp). There had been some corrosion issues with those connectors causing charge system problems.

The technician performed the inspection as suggested and found the alternator voltage defaulted to about 13.7V. When he checked for power at the alternator red wire (pin 3), there were zero volts. Next, he checked fuse #1. It was good but the circuit from the fuse to C139 was open (see image).

Confirmed repair

The technician ran a wire overlay between the fuse and C139. After the repair, the alternator charged normally with no warning lights and normal gauge operation was restored. Problem solved!