Datsun 620 Dimmer wired backwards??

[erniestr8mingin]

Hey Ratsun members,

 

So here’s the deal. Haven’t had tail lights or dash lights since the dimmer shit the bed. I bought a 2 pin dimmer for a 240Z which is a “rheostat”. It has a different pluck end, so I soldered in my old rheostat’s switch plug, but I still am not getting dash lights or tail lights. I cleaned he fuse box, replaced all fuses, but nothing. I get heater lights next to the cluster, but no dash or tail. Any ideas?

 

If it is wired in backwards, could that pose an issue, because sometimes when I turn the dimmer knob, it blows the fuse.

[datzenmike]

If only the rear running lamps are out then the bulbs are blown or the ground wire at the rear not connected or loose or the harness plug is corroded or loose. The tail lights, the front and rear side marker lamps, front parking lamps, license plate lamp, under hood lamp and the dash cluster lamps are all fed from the same position on the headlamp switch.

 

The dimmer switch only dims the heater control illumination lamps and the wiper switch knob on the '75. The '76 includes the headlamp knob illumination. The '77 includes dim-able dash cluster lamps.

 

 

Unplug the dimmer switch and check the parking lamp fuse. I believe its the right side of the fuse box closest to the driver. Has a Green/Blue wire to it. If the fuse is the cause, the dash, marker, front parking, rear running, license and under hood lamps should now work. If the fuse blows then you have a wire to one of these lamps touching ground.

[erniestr8mingin]

Thanks for the info datzenmike. The fuse is good, if I unplug the dimmer, will the lights work still? If I’m not mistaken, the lamps in the cab are grounded through the switch. Where is the ground in the rear of the truck?

[erniestr8mingin]

Anything in th dash that could be touching ground that should not be? I can’t think of any actual wiring behind the cluster that could be...

[datzenmike]

I believe the dimmer only dims the heater controls so you can live without them if unplugging it works.

 

If the fuse is not blown then you should have side marker, front parking etc... do you???

 

Are the side marker lights working? and only the rear tail lights not?? If so, then it has to be the lights and not the lighting system itself.

[erniestr8mingin]

No dash, side marker, front park, or tail lights. When I get home from work, I’ll unplug the dimmer. Checked all lights up front, everything is good and no hot wires are touching ground. As for the rear, everything is good back there, but the license plate lamp isn’t plugged in, but away from any metal to short to ground. Where are the ground wires for this circuit? I have one from the - battery to the head, then another ground strap from the head to the cab behind the battery. There is two ground wires going the metal on my radiator, and then the dimmer. What others am I missing?

[datzenmike]

It's unlikely ALL ground returns are missing.

 

The headlight switch has 2 Green Blue wires. One goes to the fuse box. The other has 12 volts when the switch is pulled out to the first and second positions. I guess make sure the switch is working first.

[erniestr8mingin]

Thanks datzenmike, I’m going to work at it tonight and see what happens. As always, I appreciate the help.

[erniestr8mingin]

Hey Mike, found that the issue is in the cluster, where the black wire goes into the cluster through the round plug. It burnt the little copper strip on the green circuit board. How can I repair this? I’ve tried using solder, but it doesn’t seem to hold.

[datzenmike]

A burnt strip might indicate that there was too much draw. If you fix it maybe the cause is still there?

 

 

Clean the copper trace ends with fine emery paper, get it shiny. Clean an inch at least. Clean it with Q tip and nail polish remover.  

 

Get a bare copper wire that bridges the gap and tin it with solder.

 

Dab some solder flux on the copper strip ends and place wire across the gap.

 

Have someone hold down on the copper wire in the middle with a wooden pencil end so it does not move around. Wood won't conduct heat away.

 

Hold a pre-heated soldering iron on top of the wire and press down gently while dabbing some electrical solder to the hot tip.

 

There may be a hissing from the flux and the solder should melt and run down onto the wire and the strip, flowing out onto it.

 

Remove the soldering iron and DO NOT MOVE til the solder cools and hardens.

 

Now do the other side.

[erniestr8mingin]

I’m pretty sure I fixed the problem. Insufficient grounds that I tested with a power probe.

[erniestr8mingin]

I’ll try that and see if it works, thanks!

[cruznude]

It must of worked we never heard back.

[don51o]

old Datsuns: too many oxidized connections & check the grounds