So the board has slowly been coming to life. I figured out that some circuits (modular disconnect and flashers) are reverse polarized. So instead of sending a current as signal, grounding the signal wire trips the relay.
I meant to suggest that to you a while back, but apparently I forgot to. Sorry!
The only switch that is still stumping me is restoring the backup alarm. It has a labeled wire which gets power from the relay board when I put the truck in reverse. From there though I can't make the siren turn on. This has to work or I can't legally drive the rig...
When you say "siren", I assume you are referring to the backup 'beeper' alarm, right? It would be illegal to drive with the emergency siren going since you are not an emergency vehicle, but I'm sure you know that.
Since that's been going well I also started working on pulling other elements into the heads-up display. I have no use for the patient code lights, but if I can make the compartment or door signals working that would be cool (not really important or helpful, but cool). All I really want is to get the board illumination working, but this far I can't figure it out. Jumping power or ground to the labeled wire doesn't do anything.
Normally, that would just consist of a circuit from the vehicle dash lights to the illumination terminal of each switch, just like any add-on switch or gage, but in this case I don't know. Those from the donor vehicle look like
Carling Contura II or III V Series switches. The much older ones had incandescent backlight bulbs, and the newer ones are LED. Some of the first generation LEDs needed a small voltage regulator circuit to fire them, so if yours are LED you might look for something like that. Also, they have two bulbs in each switch. One (usually green) is the dash light and indicates the presence of power, and the other one (usually red) lights when the switch is activated. The newer LEDs can even have a controller that can adjust things like brightness, flashing, and lockout. Here are the
Switch Circuit Diagrams, but the trick is figuring out which switch you have, and you have several types.
I have managed to get the amp and volt meter displays up and running, so that's a start! What's funny about that though is one amp wire is labeled amps signal P and one is amps signal -. The - gives a really negative reading while the p gives a correct reading. Also the volts were supposed to read from the modular disconnect circuit, but that gives a rather inaccurate and volatile reading compared to jumping power from somewhere else on the circuit board.
I have an idea about the AMP meter, but I'll come back to this one after a little more research.
I will say that there is no underestimating the complexity of the ambulance wiring. For example, I never would have dreamed that removing the cab switch board would have killed my reversing lights, but somehow they only come on when a board (any board) is connected up front.
Some vehicles use a negatively switched backup light switch also, so check the switch mounted on your brake pedal to find out which type you have.
Good luck and just remember, I'll be going through all of this in a little while also.
