no lights in my 78 200sx

[HerNameIsHarvey]

I had a buddy jump it for me but he put the cables on backward. Now I dont have lights anywhere. No headlights, tail lights, dash nights... the only thing that works in the dash is the speedometer which lead me to believe it was just a fuse issue? I only found a fuse box with 8 fuses, replaced the sketchy looking ones and i still got nothing. 

 

[datzenmike]

Check the fusible links. They are located near the positive battery cable usually. My 710 has them near the volt regulator with all the other relays in that black box near the battery.

[LenRobertson]

What datzenmike said. On my '79 SX there are two fusible links - heavy wires with plastic connectors coming from the battery positive terminal. Usually if these burn out the insulation around the wire will bubble up, but I had one once that was just broken inside. Stick your test light or meter probe up in the connectors on both sides of the fusible link (or links if you have two). Probably your test light will show power on the battery side, but not on the other side where the link supplies power to the wiring harness. There are articles online and probably here on Ratsun on making replacement links. The fusible from a different model Datsun like a 620 may work (or not). I know I replaced mine with a used one from another Datsun, but maybe it was another SX.

 

While I think your problem is a bad fusible link, I'll add another couple of ideas. My '79 SX headlights don't work. I have power at the headlights and continuity through the headlights themselves. Tracing the headlight circuit on the FSM wiring diagram I concluded it must be a bad ground. Just this afternoon I hooked a jumper wire to a broken off stub of wire coming out of the harness near the oil filter. The FSM shows this to be about the location of the headlight ground wire. When I hooked up the jumper I had working lights. Now I just need to put a permanent wire to that stub

 

My '79 also as a relay under the dash on the passenger side that controls the instruments (other than the speedo) and maybe the taillights (can't remember for sure). I replaced the bad relay with a toggle switch. If I don't switch it on I don't have any working instruments. If I forget to switch it off, I'll have a dead battery overnight. I really need to get a new relay. Anyway, the headlight ground and relay are a couple of things to check if replacing the fusible doesn't fix everything.

 

Len