Datsun Roadster Forum-311s.org

Trying to replace the original 4 pin headlight relay with a SPDT relay.I’m following the wiki diagram but I’m not completely sure I’ve got the terminals correct. The headlights come on but don’t switch from hi to low. Don’t know if they are actually on low or high. Can someone explain what the SMDB letters stand for in the attached diagram and provide a simplified schematic of where the original relay wires connect to which terminal on the SPDT relay? Also, do I need to ground the relay or is it internally grounded through one of the terminals? Thanks. Dave.

B = Battery (or from fuse)
D = Dim (or low beam)
H = High beam
S = Switch (dimmer switch)

I don’t know what year your car is, but this circuit doesn’t work for a 70 model car (I think it’s only the 70 that is different).

Peace, Pat

No ground is needed, the switching all takes place in the hot leads except that the S marked grounds via the dimmer switch.

Ok. That helps. I’m installing the new SPDT relay because the car, a ‘68, didn’t have a headlight relay when I got it. Just the four wires on the wiring harness that I need to connect. They were marked by the previous owner matching the 1-4 terminals on the original relay. I just need to know where they connect to the new relay terminals. I’ve used the wiring diagrams to help identify the wire colors and they seem to be marked correctly. Headlights are working but not switching hi/low. Maybe it’s the dimmer stalk switch.

DKB59 wrote: Tue Oct 17, 2023 6:54 pm Ok. That helps. I’m installing the new SPDT relay because the car, a ‘68, didn’t have a headlight relay when I got it. Just the four wires on the wiring harness that I need to connect. They were marked by the previous owner matching the 1-4 terminals on the original relay. I just need to know where they connect to the new relay terminals. I’ve used the wiring diagrams to help identify the wire colors and they seem to be marked correctly. Headlights are working but not switching hi/low. Maybe it’s the dimmer stalk switch.

If you want to keep it stock, member Solex68 has a new old stock OEM Relay that is listed on eBay. I'm sure he can cut you a better deal through 311s eliminating eBays 15% cut.

After more searching I found the relay wiring schematic that Curtis posted in the wiki for the Bosch style relay. Simple. I was just missing the jumper from the hi/low switch.
Everything now working!