NissanDiesel Forums

Hi, thanks again for the use of the website and all the help.

First off, my taillight circuit has a short in it (blowing fuses), it is grounding somewhere and i can't find it. However my headlights seem to work fine....

Anyway i seem to have lost my gauge lights and coolant and fuel gauges (unsure of speedo). Though my idiot lights still work fine (glow plugs, brake, filter, etc.). I was wondering if the taillights and gauge lights are on the same circuit? If so, that doesn't explain why my gauges aren't working....

I read somewhere on here there is a voltage regulator on the back of the gauges, i had my gauges off recently and couldn't seem to find it... This seems like it would be a likely problem...

Can someone help me out here, in regards to the voltage regulator? It is an 84 SD25.

Thanks again.

Complete system diagram is here, but you'd better have fresh highlighters. It's dense.

hondaguy wrote:First off, my taillight circuit has a short in it (blowing fuses), it is grounding somewhere and i can't find it. However my headlights seem to work fine....

Taillight-specific wiring is here. Notice that they're fed from contacts 36/37 on the multifunction ("MF") switch, the headlamp portion of it in . . .

Anyway i seem to have lost my gauge lights . . . I was wondering if the taillights and gauge lights are on the same circuit?

See the illumination schematic and you'll notice that MF switch 36/37 are again in play. IOW, fix the tail lamp problem and your dash lights will return.

. . . and coolant and fuel gauges (unsure of speedo).

See the instrument cluster schematic. The voltage regulator for the fuel and temp gauges is actually integrated into the cluster, IIRC. You won't find it easily. However, it's unlikely to be the problem. When they go bad, you tend to get abnormally high or low readings on both gauges at once, rather than no indication at all.

Check for power at pin 23 at the cluster (see above diagram for location of pin 23 in the harness plug). Better yet, according to the next page, check fuse No. 4 for power with Ign. ON. If no power, look hard at both sides of the fuse. Tip: on glass fuses, don't check visually, use a meter or light. I can't count how many "good" fuses have become desoldered in the cap.

If you have power at fuse No. 4, then check pin 23 at cluster. If power there, ground the temp sender lead momentarily (do not ground it and leave it that way, it'll burn out your gauge) and just flick the Ign switch ON and OFF, see if the temp gauge moves. If it doesn't, and you have power at cluster pin 23, momentarily ground cluster pin 26, repeat Ign. ON and OFF. Still no temp gauge movement? Time to pull apart the cluster, either bad gauge, bad cluster voltage regulator, or bad PC film.

Because of the magnitude of the alterations you've accomplished, I would be looking hard at wiring rather than switches, modules, or regulators.

How, looks like i have some work ahead of me,,,,,

Also, it appears that my gauges do work after all, it was not up to operating temp when i checked.... (and my fuel sender is bad)

I will start looking through the schematics and let you all know how it goes tomorrow.

Thanks again, you guys make it easy to keep an old truck on the road.

I've been looking for the short for a few days and i don't think i'm going to find it. I know i can simply run a circuit to my taillights from my headlights, since they will come on at the same time anyway, but is there a way i can also run a circuit from my headlights to my dash lights?

I guess what i am saying is, what wires do i need to run behind the dash that run the backlights of the gauges?

Or, even easier does someone have a schematic of the gauge assembly?

Thanks

hondaguy wrote:Or, even easier does someone have a schematic of the gauge assembly?

In my first post (above), see the linked words, "the illumination schematic": click on them. On the resulting page is the instrument cluster wiring diagram, and if you back up one page to EL-67, you'll see the schematic too. So you have both: wiring diagram and schematic.

However, when it comes to electrical troubleshooting, I almost never advocate a patch without understanding the cause. If a fuse is blowing, discover the cause, don't wire around it. I guarantee you'll have to revisit the same circuit again in future. BTDT.

While I only wrote seven sentence/paragraphs, I took a good half-hour to reply to your original question, plus I scanned the FSM for the pertinent diagrams. I'd appreciate your taking some time to read it all. While I frequently make misteaks, I used to sit at a bench and repair electronics for a living and can usually find my way around both a wiring diagram and a schematic. I've even found several errors in the FSM.

Hi, yes i do realize that it must have taken you a long time to write uo that reply, i am very gracious for it, and all the other help as well. It was my mistake, i had only looked at two of the links before and neither had information on the actual backlights...

Sorry, i get ahead of myself sometime. Once again, thanks for all the help. I don't want to bypass the circuit any more than the next guy, but i am at my wit's end, and need to get this street legal very soon, in order to sell my ford to pay bills!