FAQ
TL;DR: Seicento 900 low beams run “directly from the switch,” not a relay; one owner reports 15 years trouble‑free. Check bulbs, then power. [Elektroda, wojtek1234321, post #16634914]
Why it matters: This FAQ helps Seicento 900 drivers quickly restore dipped beams and avoid misdiagnosis, even when other lights work.
Quick Facts
- Bulb type noted in-thread: H4 dual‑filament headlamps for low/high beam selection. [Elektroda, nikusert, post #16634465]
- No separate dipped‑beam relay; power feeds from the steering‑column “spider” switch. [Elektroda, wojtek1234321, post #16634416]
- Verified fix in this case: replacing both low‑beam bulbs restored operation. [Elektroda, przemonk25, post #16635386]
- Fast checks: jump a bulb with wire to the battery; verify lamp power using a 12V/4W test light. [Elektroda, nikusert, post #16634383]
- Known edge case: rear‑lamp grounds overheat; add short body grounds to stop “Christmas tree” effects. [Elektroda, wojtek1234321, post #16635299]
What usually causes Seicento 900 low beams to stop while other lights work?
Start with the bulbs. In this thread, both dipped‑beam filaments were gone and new bulbs fixed everything. If bulbs test OK, check power at the headlamp connectors and fuses, then inspect the column switch. “Fix the simple things first” works here. [Elektroda, przemonk25, post #16635386]
How can I quickly test if an H4 bulb is blown without fancy gear?
Use a jumper wire straight from the battery to the bulb terminals while observing polarity and avoiding shorts. Alternatively, make a 12V/4W test lamp and probe the bulb and socket. If the bulb lights on a direct feed but not in‑car, chase power and ground. [Elektroda, nikusert, post #16634383]
Is there a dipped‑beam relay on the Seicento 900?
No. “There is … no light ‘switching’ relay, only directly from the switch,” often called the spider beneath the steering wheel. A faulty stalk can therefore drop the dipped beam even when other lamps work. [Elektroda, wojtek1234321, post #16634914]
Can both low‑beam filaments really fail at the same time?
Yes, it can happen. A responder called it unlikely but possible. The OP then confirmed both filaments had failed. Replace the pair to restore symmetry and brightness. Keep spares in the glovebox. [Elektroda, 2920901, post #16634348]
How do I check for power at the dipped‑beam circuit without a multimeter?
Probe the lamp connector or the dipped‑beam fuses using a simple 12V/4W test light. If it lights, the circuit has supply; if not, trace back toward the switch. This isolates bulb versus supply faults in minutes. [Elektroda, nikusert, post #16634383]
Where are the most common weak points besides the bulbs?
Grounds. The rear lamp grounds overheat and go high‑resistance, producing a “Christmas tree” of weird indications. Add short, dedicated ground wires from lamp grounds to the body to stabilize lighting. This also reduces voltage drop. [Elektroda, wojtek1234321, post #16635299]
Will the column light switch overheat without relays?
Owners report long service. One driver has 15 years on the same car with no light‑switch failures. The H4 system selects low or high, not both together, which reduces load. “Is it boiling? Well, rather not.” [Elektroda, wojtek1234321, post #16634914]
Does the Seicento 900 definitely use H4 bulbs for the headlamps?
Yes. Participants identified H4 bulbs in this model. That means each front bulb contains both low‑ and high‑beam filaments. Replace bulbs in pairs to match color and output. [Elektroda, nikusert, post #16634465]
How do I diagnose Seicento dipped beams in three steps?
- Test each bulb directly from the battery with a wire.
- Use a 12V/4W test lamp to check for power at the headlamp plug/fuses.
- If bulbs and power are good, inspect the steering‑column switch and its connector. [Elektroda, nikusert, post #16634383]
What tools do I need for quick roadside troubleshooting?
Carry a short jumper wire with insulated clips and a 12V/4W test lamp. These two items let you confirm bulb health and supply presence fast. They also help distinguish ground versus feed issues without a meter. [Elektroda, nikusert, post #16634383]
After fitting new bulbs, anything else to verify?
Confirm both low beams illuminate, the aim is correct, and connectors sit tight with no heat discoloration. If one side is dim, clean contacts and recheck grounds. The OP reported immediate success after a straight bulb swap. [Elektroda, przemonk25, post #16635386]
Could a bad stalk (spider) switch kill only the dipped beams?
Yes. Since the dipped circuit runs directly through the steering‑column switch, worn contacts or a loose connector can remove power only from that position. Inspect and refurbish or replace the stalk if tests show no feed. [Elektroda, wojtek1234321, post #16634416]
Why do some users worry about load without relays for all lights?
One commenter noted many lamps sit downstream of the switch. However, experienced owners state the setup works and doesn’t boil the switch under normal loads. Design choices and H4 selection logic help. [Elektroda, wojtek1234321, post #16634914]
What’s an example of a failure that doesn’t involve the front bulbs?
Rear‑lamp ground faults can back‑feed and create odd lighting behavior that confuses diagnosis. Add direct grounds to the body to stop heat‑darkened contacts and voltage drop issues. [Elektroda, wojtek1234321, post #16635299]
How rare is a two‑bulb failure, and what should I do?
It’s uncommon but real; this thread documents two failed dipped filaments at once. Replace both bulbs and re‑test before chasing wiring. Keep a spare pair to minimize downtime. [Elektroda, przemonk25, post #16634443]
I will buy new ones and let them know 
