ET-201 discusses adding fuses, how big the fuse, and what to put on a single circuit.

At 09:49 AM 4/13/02 +0200, Hans Duinhoven wrote:
>.... I plan to add a line fuse for the lights. What rating should it have?

Here's the generic answer:
Total watts/12volts=ampers
Fuse should be about 50% larger than the maximum current draw.

>I have converted the original sealed beams to H4 halogens and I still use the sidemarker lights.

Halogen single headlamps should be 55-65 watts each on high beam. I think 100 watt headlamps are illegal in the US (but never heard of anyone being ticketed for it). Front and rear parking lamps are 6 watts each. Side marker lamps 2-1/2 or 4 watts each. License plate lamps usually 4 watts each (probably 2 bulbs). Brake lights, turn signals and four-way flashers are 21 watts each. Dash illumination lamps could be 1-3/4 or 2-1/2 watts each (unless replaced with higher output bulbs). Map light may be 4 or 6 watts. Courtesy lights that come on when the door is opened are usually 6 watts each, but retrofits could be as high as 21 watts. Interior dome light (if the GT has one) would be 21 watts.

>I'd like to fuse the complete lights circuit or should I fuses the dash seperately from the rest?

It would be nice to have the headlights on a separate fuse, or even a fuse for each lamp (if you took the time to run separate wires back to the dipper switch). Many newer cars have a time delay resetting circuit breaker for the headlights, so if it shorts and trips off it will come back on after a bit, and if the short persists it will cycle off and on (with a fairly short on period and longer off time).

Please don't bodge the wiring. Crimp or solder all wire connections (except plug-in connectors), and leave no bare conductors. If you modify the wiring harness do a nice job of tape wrap afterwards, just so we don't have to rag on you as the DCO or DPO in future notes. And any change from stock specification should be documented for future maintainance.

Barney Gaylord
1958 MGA with an attitude (and only 2 fuses)