Lights?!?

[Nic.Durrant]

I have a 1990 D350 that i have owned for about a year now. I have got some modifications on it like a cold air intake, 4in exhaust system, and a boost, EGT, and trans gauges. I have got a major problem with my lights on my truck. It has all started when i got the gauges installed. I have been burning up fuses left and right. When i put a new fuse in, it will burn out in about 30 seconds and there will be some smoke coming out from under the dash where the fuse box is. I have got about 27 light that i have on my switch and the switch that i have is a 50 amp switch. Also when i put in a new fuse in and turn the lights on the backend lights will not turn on but the front half will. So my friend and i think it mite be a short somewhere but we're not sure. So if you guys could give me some info on what you think i would appreciate it.



Thanks Nick

 

[PBJ2500CTD]

27 lights???!!! Without knowing how you have connected the lights to the wiring of the truck I'd say the weakest link (wiring under the dash) is melting away. What size fuse are you using?

 

[Nic.Durrant]

Im using a 30 watt fuse.

 

[PBJ2500CTD]

Ooohhh... My imagination needs to be contained here Nick...

So you are using a 30 AMP fuse. What circuit are these 27 lights hooked into through the 30 AMP fuse? What was the original fuse size in the circuit you are using? Oh, and what bulb class or number are these 27 lights? Are they all on at the same time with the flip of the 50 AMP switch? What else is hooked into this circuit?

I don't know if you see where I am going with this, but my armchair troubleshooting leads me to believe you are WAY overpowering the circuit in the fuse box. There are few if any circuits there that can handle 30 amps. Most are 5 to 20 amps. You just CANNOT pop a bigger fuse into the socket without the "magic smoke" leaking out of the wires. When that happens you may be greeting your local fire department or setting your truck up for some major wire surgery. Depending on the current draw of the circuit you may need to set up a separate fused circuit using a relay to provide sufficient battery power. And check the wires where the smoke was coming from to insure the integrity of the insulation is still good... don't want any surprise short-circuits while driving down the road...

 

[Nic.Durrant]

The lights are hooked into the 50 amp switch. The original fuse is a 30 amp fuse. All of the lights come on except the head lights. The head lights come on a different switch.

 

[PBJ2500CTD]

Going back to the simple test - since all was/is (assumed) good before the gage installation I would check any wiring that was added, moved or otherwise involved during the gage installation. The smoke is a clue that something un-good is happening. Locate the smoke source to see if there is yet another issue about to add to the situation. For the rear lights to not work and the fronts do, something must have let go. Bad connection somewhere. Start tracing the wires looking for breaks and shorts, and check all grounds.

 

[BGore]

Echo ..

I agree with PBJ's assessment. The wiring on our trucks is really "just big enough" to support OEM loads, so there's not much extra capacity, especially as the wiring ages. Many of us have installed relays after dealing with melted wiring harnesses and replacing headlight switches just for the designed-in headlights.



I highly recommend the relay route. The trucks are capable of supplying the necessary power, the manufacturer-installed wiring is the limiting factor. There are several ways this problem can be solved, but I would recommend installation of a separate #12 wire to the battery, with a weather-protected 20AMP fuse near the battery end. Feed this wire to one side of the switched contacts on a relay, then connect your lights to the other side of the relay. Connect the relay's control input to another lighting circuit on your headlight switch of another switch if you prefer.



If you really need 30 AMPS, increase your wire size to #10 and use a 30 AMP fuse. That's a lot of power though!



You should also be sure to check your truck's body grounds, since bad grounds can put all sorts of strange loads on your wiring.



Good luck!

 

[R C Cola]

Wiring Woes

Ditto on the small wires from the factory. I also use relays now after many fixes along the way. Headlite switch is a known weak spot w/o any extra lites. This problem most likely would have come up even if the gauges were not involved. I seperated my running lites into their own circuit, and likewise with the headlites. Using relays the fuse box is not involved, except as the trigger for the relays which uses very little power and does not overload the fuse box. If you disconnect one group at a time you should be able to narrow the problem down and resolve. Good Luck

 

[Nic.Durrant]

Thanks you guys for your feedback. I took apart my dash today and there was a red wire that lead to one of my fuses. I followed that red wire and it lead me to the 3 gauges i had installed. There was a black wire that lead from the gauges into the fuse box too. It wasnt in one of the fuse. So i took the red wire out of the fuse. I put a new fuse in and all of my lights came on. The fuse did not blow out and there was no smoke coming from the fuse box. So thanks again for all of your guys help.