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You can use standard automotive blade fuses in place of any missing circuit breakers. The 12v relays will also be an off the shelf item at most autoparts stores. The 24v coil relays you will probably have to order, so probably best to just order them both. The original spec calls for 4 and 5...

Inboard of the spare tire is the polarity protection device, or in your case it is called the LBCD. The battery power flows thru the manual disconnect, thru the remote disconnect(large relays) and to the LBCD. At the LBCD input it splits to the alternator. The LBCD has 2 large diode banks in...

The ones under the cab on passenger side are remote start switches...

Unless of course they are the knuckleheads(or knuckledragers) who broke it in the first place:)

Assuming there is some sort of spring that holds the purge valve closed? Is it intact? That metal may have come from a spring coil? Failing that, the wire may have scratched/damaged a surface or the o-ring that it should seal against. As long as you are sure there is no air leaking down the...

For the A1 CB79 is ignition(switched) power and CB43 is battery power to the Trans controller...

Or something else in the system broke down and provided crap. Took apart an old style dryer last week that was full of brass shavings from input port down to the filter. The filter/media should however keep that from getting to the purge valve. If it is a stuck purge valve, Maybe you got a...

There should be 3 lines attached to the dryer. Main airline in from the compressor, dry air out to the wet tank and a third small airline should connect near the purge port/cover. that line runs up to the governor. On the old style units it is a 1/4” line and it connects right up into the...

The output of both pumps are tied together. But check valves in the pumps are supposed to keep one pump from back-feeding the other. Since there are 2 check valves inline in each pump, I don’t see that being a problem, so one of two things could be happening. 1. One of the pumps might be...

Trans power comes from CB79, you need it to power the trans which in turn gives you a neutral start relay to start the truck. Could be low power and it pulled more current than cb79 could handle...

What happens when you disconnect the purge airline off of the bottom of the dryer? When the governor reaches pressure and unloads, it sends system/sense pressure down that line to open the dryer purge valve so it can back-flush the coalescing media with air stored inside the dryer housing. If...

I wouldn’t think the exhaust brake would be engaging with the transmission out of lockup... Are your front glad-hands vented? I could see if the service glad-hand was capped and one of the service 2ways were leaking, air trapped in that line could start to override the pedal as you let off of...

I am not a bg fan of these electrics, maybe it is the old school in me liking full sweep mechanical gauges. I would be very inclined to install mechanicals if a gauge breaks here and 85PSI pressure switches to drive the horn and idiot lights... The twitchy sticky nature of these gauges may...

Interesting, that is backwards from how I am used to most electrics working... An open in the circuit or failed sender should give you a low reading so you know something is wrong, not the 120PSI reading you are liking and expecting to see on a properly operating air aystem:)

True, the 12v lead is the neg terminal of the 12-24 set of batts... I didn’t catch that in the OP’s question. for maint work it would be better to disconnect both 12 and 24. played around with the instrunment shunt today. If the spec I found is correct 100MV across the shunt = 1000A...

Well if it is already reading full, grounding the sensor lead won’t change anything, as low resistance to ground would indicate full needle deflection. If you disconnect the leads at the top of the sender then turn on the main power the gauge should fall to zero with no circuit thru the...

oops, double-tap...

You didn’t say what year/model, A0 or A1? On the A0 All of the gauges run on 24V provided by CB77... The air gauges can get wonky if the senders are not grounded properly... the sensors are under the drivers dash and are screwed into T fittings and into a 2way check valve that provides park...

Yep, both 12 and 24 are referenced to ground, so a single disconnect on the ground lead will isolate both voltages... whichever way you go, the one on the 24v lead or ground needs to be large enough to handle peak current flow to the starter...

You don’t have to take the bumper off, just the center skid plate, about 6 bolts... got rid of mine as well as the 2ways under the drivers floor. Kept the check valve though, and put a pair of male quick connects on it and use it to backfeed the QC I put on the wet tank...