ENGINE SWAP GUIDE - ELECTRICAL HT4100 to Olds
As mentioned previously, one of the challenges of a 4100 swap-out is that some of the systems (Cruise, Warning Lights, Climate Control, etc.) are integrated into the ECM. Armed with the factory service lit and troubleshooting diagrams, as well as some real-world experience on these cars, I've put together some easy-to-follow solutions for each. Personally, I like to re-use as much factory wiring as I can, use solder and shrink tubing, and attempt to make the modifications look like it rolled off the assembly line that way. But, if you prefer a more 'quick and dirty' approach, there are some options for that as well.
Assuming you're converting to a carb, DO remove the fuse and relay for the fuel pump circuit which are marked on the accessory fuse block under the driver side of the dash. DO remove the two 3 amp fuel injector fuses. The in-tank pump operates at around 14PSI and will flood your carb. A mechanical pump will pull through it fine.
The original HT4100 made use of an engine harness utilizing "two" firewall connectors. One is the 6-sided “environmental bulkhead” connector on the center of the firewall and contains mostly low current, signal level I/O to sensors and actuators. The other is a square-looking center bulkhead connector (immediately adjacent to the enviro conn) which contains the more conventional circuits, like the alternator feedback/warning light, AC compressor, starter solenoid wire, etc. Really it's two halves that share a center mounting screw; one half for the engine, the other half for engine bay components. For engine removal, leave all the harnesses in place and just disconnect these two connectors.
Once the engine is out, whether on hook or on stand, go ahead and disconnect all of these engine connections, being careful not to break their clips. Retain the harness for your new engine. Resist the urge to cut any wires at this time.
GAUGES & WARNING LIGHTS
You really don't need to do anything different here. This warning light is used as part of the alternator excitation circuit, which is pretty standard for most OEM charging systems. If you plug in the 2-pin flat-blade connector to your new alternator exactly like the original was (or just bolt the 4100's alternator in), this light will work correctly and your battery will charge properly. However, you may need to extend this wiring if your new alt/bracket package is out of reach. Same goes for the +12v charge wire from the alt to the batt. Play it safe here...that batt wire is unfused.
Even with an aftermarket temp gauge, there are good reasons for keeping your Coolant Temp light, especially with an analog dash where it'll grab your attention. Below are several options.
You could keep the 4100's temp sensor and wiring and screw it into an open coolant port; the ECU doesn't care what engine is sitting under that sensor, so long as it's connected. But it's important that temp sensors are in flowing coolant, which rules out the rear heater port location on an Olds intake. Plus 269F is a little hot for my liking. Be sure the 4100's harness ground eyelets get connected to the engine.
→ If you have a digital speedometer, then the Coolant Temp lamp is in the left “Info Center” panel. You would connect to the dark green wire at position 17 of the left side IC connector and it should light up.
→ If you have an analog cluster, then the light is in the top right of the speedo face. Grounding/connecting to the dark green wire at position 12 of the connector behind the right side of the cluster should light this up. These clusters omit the bulb in the left info center.
In either case, simply trace this wire back to a convenient place to cut and splice to your new temp switch under the dash. The diagrams below can assist also see the Docs Page for additional diagrams. If you want to make use of the old sensor wire to re-route to your new switch, it's yellow wire ckt 410, which goes through 'D' in the environmental connector; clip it under the dash and wire it up.
And as Columbo says, just one more thing....If you'd like your Coolant Temp light to come on as a bulb check when cranking, the way it originally did, run a wire from position 35 of the ignition switch (this should be an empty terminal) to the side of the bulb you've connected the new temp switch to. When you turn the key, it grounds out 35 and your bulb should light.
Stop Engine – Temperature:
There are two pieces of data that are important for the climate control: 1. Outside Temperature. 2. Coolant Temperature.
Outside temp is obvious, but why coolant temp? It's because the CC Head needs to know if the engine is warmed up or not before it switches on the blower when Heat is called for, so it's not blowing cold air on your feet.
So, for a functioning Climate Control, you have 3 options:
Colors and terminal locations provided below for the circuits worth keeping, and those you can dispense with. You may want to retain a few of these for future circuits (like gauges). If cutting off, stagger your cuts to avoid shorts, and leave a little length so you can hide these wires in the convoluted tubing. Shrink tube or elec tape on wire ends is a good idea, too.
It's possible colors may vary year-to-year, but I'd expect connector positions to be reliable. Info below from the 1984 Diagrams.
On the Environmental Connector: KEEP …. if retaining the ECM. If not keeping the ECM, you can also omit the following, using none of the Enviro Conn circuits.
I (lt grn): Outside Temp Sensor
U (blk): Outside Temp Sensor Return
N (tan): Ground Eyelet (ground to engine)
D (yel): Coolant Temp Sensor
T (blk): Colant Temp Sensor Return
V (blk): Ground Eyelet (ground to engine)
On the Center Bulkhead Connector Half: No Longer Needed (see image & caveat below)
Note circuit numbers are given; see following chart to convert to terminal position
333 (tan): Brake Low-Vacuum Switch
120 (lt blue): Oil Pressure switch signal for Fuel Pump
435 (brn): EGR
436 (brn) AIR Valve
426 (dk blue): ISC
425 (lt blue): ISC
429 (blk/pnk): AIR Valve
639 (pnk/blk): Common for AIR valves, Canister Purge, EGR
On the Center Bulkhead Connector Half: KEEP (see image & caveat below)
420 (ppl): Transmission Connector Ckt “A”
422 (tan/blk): Transmission Connector Ckt “D”
204 (dk blue): AC Clutch
402 (grn): Cruise Servo Power Solenoid (ground return is local to block)
403 (dk blue/wht): Cruise Servo Vac Solenoid
86 (brn): Cruise Servo Vac Solenoid Return
6 (ppl): Starter Solenoid
438 (dk grn/wht): Transmission Connector Ckt “B”
3 (pnk): HEI 12V+
37 (lt grn/blk): Engine Metal Temp Switch (for warning light)
450 (blk/wht): 2 wires- one to ground eyelet which should be grounded to engine. Other to ISC: can clip this one out if desired.
31 (tan): Oil Pressure Warning Light
25 (brn): Alternator light (required for alternator to function)
Note: If you decided not to retain the ECM, I also recommend NOT connecting any of the environmental connector grounds (no enviro ckts at all, actually). If you do, your Climate Control will wait for an “engine warm” signal that's never coming, and require you to hit 'Defrost' first as an override for the blower motor to work. Thereafter, it should operate correctly until the next key cycle. If you don't connect the grounds, it knows there's an issue, and will work without waiting for ECM input. Of course without an ECM, outside temp won't function.
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