I have been working on the wiring end of my 1968 144 conversion from BW35 to manually tranny and was pleased on how easy Volvo made it.

I needed to make two changes beside running wires for the OD.

There is a switch on the BW35 that controls two functions. The backup lights and the no start unless in park or neutral. There are four wires attached to the switch on tranny. I reviewed the wiring diagram and traced back some of the wires. I knew I needed to make the backup lights work off the grounded switch on the manual tranny. The starter lockout needed to be bypassed for the manual tranny.

I found out there was a relay mounted on the firewall used for the starter lockout. A wire coming from the IGN switch goes to the relay. Off the relay and wire runs to the starter. A third wire goes to the switch on the BW35. When in Park or Neutral the relay closes and you can start the engine.

For the backup lights power goes down to the BW35 switch. When in reverse the switch on the BW35 closes and lets power flow out of the switch to the backup lights.

While looking at the owners manual I noticed the wiring diagram lists the relay on the firewall as a starter relay or backup light relay depending on tranny application. Interesting, a light went on. I looked at the relay and the wires around it. Turns out what I needed to do was pretty simple and well thought out by Volvo.

For the starter lockout. All I needed to do was pull the IGN wire and starter wire off the relay and tie together. I could then use the relay for the backup lights. The wires for the backup lights happen to be right by the relay. The power wire for the backup lights goes one terminal on relay. The other wire leading to the backup lights go to the backup lights. The third wire on the relay already went to the BW35 tranny. All I needed to do was extend and move that wire over to the backup switch on the manual tranny.

I was very pleased with how well Volvo thought out the wiring harness. I was expecting a good bit of work to make these changes and found the work had been basically been built into the harness to make the change. Almost looks factory and very close to that.

I need to run a power wire off fuse #5 according to the diagram to another relay for the OD control. Not that it matters but wonder if anyone knows were the OD relay was mounted on the 14X series? Under the dash or on the firewall.

Craig