2001 mid bus conversion electrical questions

[new2ya]

Im new to these forums so please if i offend and post in the wrong place let me know.

Ive recently purchased a 2001 chevy mid bus for a personal tiny house project. It has a rebuilt title but 45,000 miles on it and it seems to run well other then some rear brake issues i can most likely figure out.I The thing is im not familiar with some the wiring ( but im pretty darned good at wiring ). The main controls of this unit have a few buttons , the override for the stop sign, and the dome lights work fine.

The aux fan, the rear heater fan, and the rear ac dont work via the switches. If i hook up an external 12 volt power supply to the switches i can make them all work just fine. At first i thought fuses so i checked the drivers side and the ones in the above panel ( which appear to only operate flashing lights) and no issues. There is a switch labeled master switch on the panel so i thought hey maybe that disables power? So i did some checking with my voltage meter and jumping some wires all i managed to do was turn on the rear door/ emergency window alarm. This got me to thinking all 3 of the non working issues are fans which would make a fire go wild in a bus. Is there a fuse box/safety switch/or the master override im missing?

If i give it power at the switch and it works that tells me the wiring back to it is good just no voltage at the switch. Any help i would love, want this unit to be working before i renovate.

[roach711]

I'd be looking at the add-on fuse panel the bus manufacturer installed. If you're lucky there will be a panel legend telling you what's what. Some bus manufacturers will e-mail wiring schematics if you send your VIN.

[new2ya]

The only addon fuse panel i can find is in the upper part of the bus and all test good

[new2ya]

My ultimate goal is to merge this bus with an old pop up camper i have. Then eventually add solar to bus to the existing power converter from the pop up. I know the pop up electrical just not the bus. Figuring out the bus wiring is the main goal and thank you.

[new2ya]

I spent all day long working on the wiring on this unit and from what i can tell the bosch relay before the addon fuse box isnt allowing power to come thru. If i jumper it then everything starts working, that is everything but one mystery fuse that keeps blowing.

[roach711]

Progress!!!

[new2ya]

Progress but confused progress.....

Turns out the fuse blowing is going to the master switch on the bus controls which ive hard lined since i dont have that switch (it was missing). If i unjumper the master switch and bypass the Bosch continuous power relay then no blown fuses and all works. ( actually my turn signals work better no fast clicking ).

The master switch fuse is after the bosch relay so it cant be what powers the relay, but yet bypassing the relay and unhooking the connection to where the switch then everything works makes no sense. When i jumper the bosch relay i do hear a click under the dash but i cant be in two places at once so i have no idea what lies down below. Dear lord this is driving me nuts.

[roach711]

Make a remote switch to replace the relay jumper (it could be just two wires that you run from the relay then connect together to complete the circuit). Then you can look for the mystery under dash clicking.

Is the bosch relay part of the chevy wiring or the add on bus wiring? Does the main switch trigger the relay or does the relay power the main switch?

Is the fuse located between the master switch and the add on panel or between the master switch and the relay?

Most times when I've found myself thinking "this doesn't make sense" it was because I was making bad assumptions about what the circuit components were doing. Draw out a schematic of the wiring then confirm that it's actually doing what you think it is. A volt meter is indispensable for tracing power and continuity.

[new2ya]

I would just wire a switch to bypass the relay but ive worked on english cars in the past and i found out bypassing relays often leads to a fire. I found the clicking under the dash turns out its on the firewall under the hood. Its a
Hella Mini Relay, 12V, 20/40A, SPDT relay the fact that its clicking i guess tells me its at least working , not sure what it does though.

The bosch relay is not part of the original wiring its part of the bus wiring.

The fuse that keeps blowing is after the relay , the relay is what gives the whole addon bus fuse box power. Did i mention the whole fuse box is unlabeled and had no fuses in it when i got the bus? Ive only identified 2 out of 8 of the fuses , 1 to the cb and 1 to the master switch. If i remove all the fuses everything still seems to work (minus the cb and the missing master switch ) if i jumper over the relay( which just powers the fuse box , and doesnt bypass it ). What the other 6 fuses power i have no idea, i will say none of the yellow pre warning lights on the bus work with or with out the fuses in. I know im not legally allowed to use those amber light but i want to make sure everything is at least wired properly before i start going any further.

Btw the smart fuses that light up when they are blown are freakin awesome. At autozone they are 7.50 for 10 and at advanced auto they are 5 bucks for 2. Go for autozone


I dont have the original master switch it was missing when i bought the bus. I found two wires labeled master switch in the control panel so to complete the circuit i just jumped them.

[roach711]

My guess is that your main switch is the low current trigger that pulls down the relay which provides a high current connection to the fuse panel. To verify this, just disconnect/reconnect the jumper on your main switch and listen for the relay to click, then check for power at the add on panel.

So where is the fuse that keeps blowing? Is it in the add on panel or in the wiring between the relay and the panel? What's the amp rating of the blown fuse? If you pull the fuse does the entire panel power down?

[new2ya]

The fuse that keeps blowing is in the addon fuse panel which is after the relay. Thats where it gets weird the people at collins bus told me the master switch is what controls power to all of the fans in the bus ( like a master kill switch for all of them . How can something that is after the relay control whether or not the the relay has power when its the relay that powers it? The crude diagram below shows what im talking about. The little blue line is my jumper wire.

[roach711]

Originally Posted by roach711

Most times when I've found myself thinking "this doesn't make sense" it was because I was making bad assumptions about what the circuit components were doing. Draw out a schematic of the wiring then confirm that it's actually doing what you think it is. A volt meter is indispensable for tracing power and continuity.

Not saying your schematic is wrong (I've seen some pretty goofy wiring in my time) but it doesn't make sense. It's time to go back and prove your version, step by step, or find out where it's wrong.

Originally Posted by new2ya

How can something that is after the relay control whether or not the the relay has power when its the relay that powers it?

The obvious answer it that it can't. I'm betting heavily that the master switch is (or should be) attached to the relay and not the panel.

[Phatman]

Double check your bulbs in the sockets. Make sure they are 12 volt bulbs. Make sure you don't have a double pin bulb in a single pin socket. I've seen it before.

[roach711]

Here's a schematic of how a normal bosch 4 pin relay is wired. The switch across 85 and 86 energizes a solenoid that connects 30 and 87 and sends power to the add on panel. From what you've posted, there's nothing wrong with the wiring up to the panel. If the fuse that's blowing is on the panel the problem is in the circuit after the panel. Trace the wire that's connected to the fuse holder and you'll likely find the problem.

[new2ya]

Phatman are you referencing the amber lights not working?

Roach it gets even weirder , i got ahold of collins today and they sent me a copy of the schematics that they had on file for this unit. The wire colors the gauge wire, etc all seem to match factory specs. The schematic unfortunately does not show the master switch even existing. It also shows the stop sign with flashers ,dome lights, rear buzzer on the same addon circuit panel, but when i got the bus no fuses where in the addon fuse box and those 3 features worked. Ive since then sent them an email asking for schematics of the year prior and after just in case i was some sort of transition model.

I went outside tonight to do some work on the bus but man is it cold , my phone says its 5 degrees outside. I found the fuse that powers the relay but it was so cols i didnt even care to check continuity.

PS: I plan on sending you a pm about your build, i dont want to derail this thread.

[new2ya]

Roach i was typing up my reply when you posted your diagram that matches the schematics i got from collins. But see my previous post , with this wiring nothing should have worked that was bus related It shouldn't have power without me bypassing the relay.

[new2ya]

I think i may have figured out what has happened, i think someone else has done some rewiring. I think someone tried to bypass the bosch relay and they wired everything to the hot side of the relay. Some where in the mix they shorted the master switch causing a dead short. It appears they may have done this in vain because the relay isn't getting voltage to actuate in the first place. If i can track down the fuse to the relay im betting it is blown and will accurate. The only thing that doesnt currently work when i bypass the relay are the amber caution lights and legally i dont think i can even use them. When i get a day to look at it in the light ill apply 12 volts to the 86 connection and see if the relay works.