FAQ
TL;DR: On a Golf 4 (1999 1.6 SR), dimming lights and ESP/ABS after electrical loads often trace to high resistance at grounds or the battery-top fuse box; key stat: 110A alternator feed; expert: "Alternator (110A also used) 90A." [Elektroda, moto-kord, post #17365166]
Why it matters: These symptoms mimic alternator failure but are frequently simple connection or fuse-box issues you can diagnose quickly.
For: VW Golf Mk4 owners troubleshooting warm alternator cables, voltage drop, or warning lights after using windows, fans, or high beams.
Quick Facts
- Typical charging voltage seen: ~14.1–14.3 V at battery when OK; ~12.8–13.0 V when dropping. [Elektroda, grze21, post #16722813]
- Alternator feed protected by 90–110 A link; interior feed ~110 A; engine management ~50 A. [Elektroda, moto-kord, post #17365166]
- Hot alternator-to-fuse-box cable indicates voltage drop at fuse box or connections. [Elektroda, grze21, post #16722721]
- Common fault path: corroded grounds between engine/gearbox and body; clean and retorque. [Elektroda, vogelek1, post #16724822]
- Battery-top plate fuses and lugs can heat under load; inspect for discoloration. [Elektroda, ociz, post #17364297]
Why do my lights dim and ESP/ABS lights appear after using windows or high beams?
High current loads expose resistance at grounds or the battery-top fuse box. The system voltage sags, triggering ESP/ABS warnings. Fix poor ground straps and clean the fuse-box lugs before condemning the alternator. “Check all the ends of all the masses and it will be hurray.” [Elektroda, vogelek1, post #16724822]
What charging voltages should I see on a healthy Mk4 with the 1.6 SR?
Expect about 14.1–14.3 V at the battery when charging normally. Readings near 12.8–13.0 V under load suggest drop or weak excitation. Compare alternator terminal to battery terminal to spot losses. A restart restoring 14.1 V points to intermittent connection issues. [Elektroda, grze21, post #16722813]
How do I check for a voltage drop between the alternator and the fuse box?
Measure voltage at the alternator output and at the fuse-box input under load. A significant difference means a bad connection. Use headlights and rear defogger to load-test. “Check the voltage drop on this wire between the alternator output and the input to the safety box.” [Elektroda, ptr92, post #16722746]
Which battery-top fuses feed what on the Golf 4?
Layout reference: FL1 alternator (90–110 A), FL2 interior (110 A), FL4 engine management (50 A). Additional slots feed ABS pump and fan control. Knowing this helps target heat and drop points when symptoms appear during cabin or engine loads. [Elektroda, moto-kord, post #17365166]
Could a bad ground cause no-charge or low voltage only at the battery?
Yes. If the alternator shows ~14.2 V to engine ground but the battery shows ~12.9 V, the battery ground path is resistive. Clean and retorque the engine/body grounds and the negative battery cable to body. Re-test after load. [Elektroda, grze21, post #16724723]
Where are the critical grounds to clean on a Mk4?
Service the negative battery to body, the engine/gearbox to body strap, and the clusters under the battery tray. Also inspect the hood-to-engine bonding if fitted. Remove corrosion, brighten metal, and tighten. [Elektroda, kortyleski, post #16727651]
What is a strip (link) fuse, and why does it heat up?
A strip fuse is a bolted, flat metal link rated for high current (e.g., 110 A). Heat indicates resistance at the bolted joints or a fatigued link. Clean both mating surfaces and ensure proper torque. Replace if discolored or cracked. [Elektroda, ociz, post #17364297]
Could worn alternator brushes or slip rings cause intermittent charging?
Yes. Brushes wearing short or rough slip rings can make charging start-stop with vibration or load. If grounds and fuse-box joints check out, inspect brushes and rings next and verify belt tension. [Elektroda, carrot, post #16727599]
What is the exciter (thin blue) wire and its failure symptom?
It feeds the alternator field to start charging. If it breaks, the alternator may not wake up, causing low voltage and warning cascades. Inspect continuity and connector fit at the alternator. [Elektroda, Staszek49, post #16722978]
How do I fix a warm alternator cable at the battery fuse box?
- Load the system and measure alternator vs. fuse-box input voltage.
- Remove the battery-top fuse box, clean lugs, links, and studs.
- Reassemble, torque, and re-test under load for <0.2 V drop.
“Check the connections in the fuse box on the battery.” [Elektroda, moto-kord, post #16723004]
My readings improve when I ground to the engine, but drop when I ground to the battery. What does that prove?
It proves the negative battery-to-body path is resistive. The engine block ground is intact, but the battery ground cluster needs cleaning or repair. Service the under-battery grounds and retest under load. [Elektroda, grze21, post #16724723]
Do the interior and engine-management feeds share the same main fuse values?
Interior feed is 110 A, and engine management is 50 A on the referenced layout. Map your box to confirm positions, then check those joints for heat or tarnish during the fault. [Elektroda, moto-kord, post #17365166]
Edge case: Can ABS/ESP warnings appear with no battery light on?
Yes. A localized drop at the fuse box or grounds can sag module voltage without triggering the charge lamp. After a restart, contact pressure can improve temporarily, masking the issue. [Elektroda, grze21, post #16722721]
Should I upgrade the early plate-style battery fuse box to the later cable-bridge type?
Owners report the later box uses a cable bridge instead of a rigid plate. Any swap must retain correct fuse ratings and clean, low-resistance joints. Inspect and clean first; replacement follows evidence of damage. [Elektroda, mayer25, post #17364191]
What else should I check before replacing the alternator?
Verify belt tension, clean all grounds, check the battery-top fuse box for heat, confirm exciter wire integrity, then test brush length. Replace parts only after drop tests and visual inspections fail. [Elektroda, Staszek49, post #16722978]
