99 GMC 3500 wiring issues

[Clinton]

Hi all,

I just joined the forum and have been reading numerous postings for info on all things GMT400. I recently purchased an ex-ambulance so wiring has been a crazy mess. Not just the normal extras like UHF and horns, Im talking extra lighting on its own flashing system with the horn, dual battery setup, radiator coolant motor to run after engine stops, central locking, adjustable shocks from inside the cab, switches galore, 240v..anyway you get the idea. I'll attach a photo tomorrow of some of the wiring I've removed, I'll need a skip bin its pretty funny.

That aside, I'm still having some issues which I haven't been able to find on the various forums and postings.

Actually there are a few. But the main one Im hoping to get an answer for is whether all wires on the ignition switch should read battery voltage when ignition is switched to run?

I'm having issues like no tacho, speedo, temp and fuel but backlights work and most other lights seem okay. I haven't got a code reader and cant drive it at the moment to test if the trans is playing up, but it goes into drive, reverse and gear indicator lights up. I'm leaning toward the ignition switch being the culprit, but who knows. Any help appreciated.

 

[Clinton]

Also, can someone please let me know in which order the colours are for the buffer/DRAC module. I have the connector for the longer plug but the smaller one with 4 pins was cut off at some stage. I found 4 wires near by, black, grey, blue and orange, but not sure which ones connect to where. Help much appreciated!

 

[Clinton]

Disregard my last port, all sorted. If you have this issue it's the wiring for the cargo lamp - which of course on my car was changed to be something for an ambulance. Still makes me wonder if Im missing wiring on the DRAC - oh well

 

[Clinton]

This dash not working is driving me nuts. Ive taken the dash out to see if maybe Im missing something. Heres the plug at the back, can you tell me if there's any contacts missing please? I've checked the ignition switch and they seem to power up well, I must be missing something..please help

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[Chris Rogers]

your are going to have several issues . the LHD_>RHD swap will have its own nuances.

the rest of it will be a canse of working out what is original vs what has been added by the people that did the ambulance side of it. that should be fairly obvious.

 

[Clinton]

Hi Chris, you're spot on.

Here is an example of just SOME of the extra wiring added to this beast. Not to mention all the stuff I have left or which has been added to the original looms which I'm not going to unravel...

I've since worked out the temp sensor is stuffed, hence not working on the dash. The fuel gauge is showing well past full, but then again it is full to the brim in the tank so maybe okay.

I got excited to find a 4l80e under the car, I was thinking it was the 60. Unplugged the round connector and oil trans fluid was dripping out, the whole plug full of it. Maybe it explains the tacho not working? The VSS was cleaned but ran out of time to test for power.

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[Chris Rogers]

Quick run of the VIN or build sheet if it's still there should tell you more about it.

If this has a 454 in it then the tach is driven off the distributor. If it's a vortec then I would suggest pulling the diagrams from the sub forum.

Worked on a few of these over the years and they are not a fun thing to do as you are finding out.

 

[Chris Rogers]

Inside the glovebox should be the options sheet. Start with that.

 

[Clinton]

Thanks. It's the 6.5 TD. I'll try and find some diagrams.

 

[Chris Rogers]

Ahh. That's that different matter. There are diagraims for that. Let me swap to a PC.