Looking for Hot on Run in the Engine Bay

[flint54]

I have the FSM schematics, but I'm mechanical not sparky. I want to locate a "hot on run"

terminal in the engine bay, and would really prefer not to cut into a wire, even if I knew

which one. I know there's plenty of opportunities in the cab, but I would rather not stuff

a +VDC wire through the firewall. The bulkhead connector shows terminal G6 on the cab side

as hot on run, but there's no G6 listed on engine bay side. With an overabundance of caution,

I've not yet dismantled the connector to evaluate whether I can add a pinout to the engine

bay side. If I remove the small center bolt, do the two connectors demate? Does anyone

know if it is possible to add a wire/pin to the connector at G6? OR, does anyone know a suitable

"hot on run" connection in the engine bay? I was hoping the ballast resistor was, but it is not.

 

Thanks!

 

Why? SPAL fan controller wants this, in addition to the direct (fused) tap from battery.

[HOrnbrod]

The is a square connector near the ECU hanging on the end of a cable that is called the "test" connector (the DRB2 test set plugs into it). It has a switched an ignition switched 12V terminal that takes a spade terminal. That's what I used for the Spal.

[flint54]

Oh man, you're a champ!! :bowdown:

 

Figure 19, pin #5, F12 - 18DB/WT. F12 feeds

from PDC fuse #6, which feeds from A21.

 

That one really threw me a curve ball since

circuit A21 (BHD pin B6) showed as hot on

start only at the ign switch, but clearly it is

hot on run, given it powers so many items.

[HOrnbrod]

Thanks, glad to help. Another tip on wiring the SPAL PWM controller: Use the dash temp gauge sensor for the SPAL signal wire at the back of the head, not the thermostat cover temp sensor. This sensor is the engine temp feed to the ECU, and there's not enough voltage change delta from low temps to high temps to reliably trigger the fan speed from LO to HI. It's too spastic. The dash temp gauge sensor works mucho better providing crisp OFF-LO-HI fan speed signals. :cheers:

[jimoshel]

Thanks, glad to help. Another tip on wiring the SPAL PWM controller: Use the dash temp gauge sensor for the SPAL signal wire at the back of the head, not the thermostat cover temp sensor. This sensor is the engine temp feed to the ECU, and there's not enough voltage change delta from low temps to high temps to reliably trigger the fan speed from LO to HI. It's too spastic. The dash temp gauge sensor works mucho better providing crisp OFF-LO-HI fan speed signals. :cheers:

Why not use a temp sender from the head and screw it into the radiator? Or thermostat housing. Looks like with a bushing it might fit. Use the wiring already there and not have to modify. Just wondering.

[HOrnbrod]

Why not use a temp sender from the head and screw it into the radiator? Or thermostat housing. Looks like with a bushing it might fit. Use the wiring already there and not have to modify. Just wondering.

 

That's just the point, I'm using an existing dash temp gauge sensor to the SPAL. Sure you could use an additional dedicated fan speed sensor by installing one in the rad bung or somewhere, but that's adding an additional sensor you don't need and more wiring. The SPAL controller works just fine by paralleling it's temp sensing wire to the existing dash temp gauge temp sensor output wire. And the voltages from the gauge sensor are ideal for the SPAL.

[flint54]

I installed a separate Spal temp sensor using a Tee fitting into the heater hose circuit after confirming

it flows all the time whether or not the heater control is opened. Ironically, and for reason(s) I have

have yet to determine, my dash temp gauge quit responding as soon as I first powered up the Spal,

even though there are totally unrelated electrically.