so i just swapped my si with a b16a fully built for turbo an yesterday was the first time ive driven it. it runs fine but when im going down the road my speedometer drops to zero. it works at first but then drops. but when i turn my headlights off the speedometer goes back to normal.

Does anyone noe what may cause this problem?

 

spedo clips wet ans you need to wire a new one in... they get wet when you do swapps the pins in side the clip get wet.

 

Sounds like a classic bad ground wire problem.

 

but why would it work with the headlights off but not with them on?

 

Different electrical components sharing a common ground connection on a circuit will interfere with each other if the ground is bad.

Another possibility is the installation of the wrong bulb type in the parking lights or taillights.

 

how would i wire a new one in? not too good with electrical problems