Research note

Gauges, speed signal, tach, CEL (98 5VZ-FE + A/T ECM into 88 4Runner, 88 cluster kept)

How pages are cited:

RM580U = 1998 4Runner repair manual (TIS PDFs, printed page numbers like BE-42, DI-236).
EWD319U = 1998 wiring diagrams (printed page numbers like p.228).
RM077U = toyota_truck_and_4runner_88.pdf. "pdf N" is the 1-based PDF page. BE-N sits at pdf (1158+N).
RM507U = 1997 T100 repair manual. "pdf N" is 1-based.

0. A gap in the sources first

RM077U has no 3VZ-E engine sections. FI covers only "22R-E, 22R-TE" (FI-1, pdf 207). EM, IG, LU and CO cover 22R/22R-E/22R-TE. 1988 Toyota 4runner FSM.pdf (566 pages) is the same 4-cylinder book. The 3VZ-E engine details were in a separate supplement we don't have.

The BE chapter (cluster, gauges, senders) does apply to the 88 cluster. The meter-pin table on BE-24 only names 22R-E/22R-TE variants, though. So the 3VZ-E-specific sender part numbers and thread sizes are not in our sources.

Also: the cooling (pdf 323) and lubrication (pdf 331) sections mentioned in TODO.md are for the 22R family.

1. Temperature gauge

	1988 (RM077U BE-29/30, pdf 1187–1188)	1998 (RM580U BE-42)
Gauge type	w/ tach: cross-coil receiver. IG–TU ≈135 Ω, TU–E ≈138 Ω, IG–E ≈273 Ω. w/o tach: bimetal receiver ≈25 Ω behind a 4.5 V regulator	Cross-coil with a diode. A–B ≈90, A–C ≈170, B–C ≈230 Ω
Sender spec	60 °C: 146.6 Ω (+26.5/−4.0) → 142.6–173.1. 115 °C: 24.3 Ω (+1.3/−1.8) → 22.5–25.6	50 °C: 234–314 Ω. 120 °C: 24.0–30.5 Ω
Wiring	Single wire, sender to cluster A-7 (BE-24)	W2, 1-pin, Y-R → II3-21 → meter C11 (EWD p.228)

Does the 98 sender match the 88 gauge? Close, but it reads low. I fitted a thermistor (B-value) curve to both specs. B is about 4,200 K for both, so the curves have the same shape. But the 98 sender is about 1.27–1.29× the 88 sender's resistance at every temperature:

True °C	88 sender Ω	98 sender Ω	88 gauge would show about
80	71	91	73 °C
90	51	66	82 °C
100	38	48	92 °C
115	24.3	31	106 °C

Result: the 88 gauge reads about 7–9 °C (13–16 °F) cool with the 98 sender.
At 115 °C the two tolerance bands don't overlap: the 98 sender is about 27.5–35 Ω there, the 88 spec is 22.5–25.6 Ω. At 60 °C they barely overlap at the 88 band's top end.
Monch said "works", which fits: the needle moves and sits a little low. The real risk is that the gauge under-reads an overheat.
Options:
(a) Use the 88 3VZ-E sender, or any sender that meets the BE-30 spec, in the 5VZ port. Only if the thread matches.
(b) Keep the 98 sender and accept the low reading.
(c) Bench-check the sender in hot water: about 51 Ω at 90 °C means it matches the 88 gauge.
Location on the 5VZ: "ECT Sender Gauge" on the intake manifold water passage, near the fuel pressure regulator. It is separate from the 2-wire ECM ECT sensor (RM580U SF-51, Knock Sensor components; also named in the EM cylinder head removal/installation pages).
Thread size: not in RM580U or RM507U. [assumed: Toyota's usual 1/8 PT taper. Measure or test-fit before buying.]

2. Oil pressure

1998 4Runner: a warning switch only. Continuity with the engine stopped, open above 24.5 kPa (3.55 psi) (RM580U BE-43). It sits on the cylinder block, below and beside the oil filter union: precoated (thread sealant), 15 N·m (150 kgf·cm, 11 ft·lbf) (RM580U EM-77). Socket SST 09816-30010.
1988 cluster with gauges (RM077U BE-30, pdf 1188):
Bimetal receiver, A–B ≈ 44 Ω.
Pulse-type (bimetal) sender. Test: 12 V through a 3.4 W bulb. The bulb stays off with the engine stopped and flashes with the engine running. The flash rate varies with engine speed.
No ohms-vs-pressure spec exists, because this is not a variable resistor.
The 88 warning-light version is a switch that opens at 20 kPa (2.8 psi) (BE-31).
1997 T100 5VZ with gauge (RM507U BE-42/43, pdf 1836–1837; SS-76, pdf 247):
The sender is the same pulse type. LED test: off when stopped, flashes when running.
The receiver is ≈25 Ω.
It screws into the same block port as the 4Runner switch: "Oil pressure switch × cylinder block, 15 N·m" (SS-12/SS-28, pdf 183/199), same SST 09816-30010, adhesive on 2–3 threads (EM-99).
So a T100 sender fits the 4Runner 5VZ port and clears the parts around it.
RM507U gives no part number or thread size. [assumed: 1/8 PT taper, like Toyota's other oil switches and senders]
Will it read right?
A pulse sender and its gauge are a matched pair: the same current pulses heat both bimetals. The T100 sender is matched to a 25 Ω receiver, and the 88 receiver is 44 Ω. So calibration is UNVERIFIED and will probably be off: the needle moves, but the scale may be wrong. Monch only said it works.
Best choice: an 88-type sender (the 3VZ-E or 22R-E part) in the 5VZ port, because it's matched to the 44 Ω gauge.
Second choice: the T100 sender, checked against a mechanical gauge. Spec: idle ≥29 kPa (4.3 psi); 3,000 rpm 245–520 kPa (36–75 psi) (RM507U LU-1, 5VZ, pdf 1113).
Wire: II3-22 G-W (the 98 oil switch circuit) → 88 N3-8 L-B.
If you'd rather have a warning light only: the 98 switch works with an 88 warning-light circuit (the switch grounds the bulb). It does not work with the gauge.

3. Speed signal (98 ECM SPD/SP1, E12-12 G-O)

What the 98 ECM expects (RM580U DI-236 to DI-238; Terminals of ECM SPD; EWD p.228/229):
A "4-pulse" square wave.
On the 5VZ-FE the source is the ABS ECU: wheel sensors → ABS ECU → combination meter (C10-A2, GR-L, marked "*1 = 5VZ-FE") → meter waveform shaper → meter A1 G-O → ECM.
The ECM pulls the line up internally to 5 V (DI-236 diagram shows 5 V). The check is 4–6 V, "voltage generated intermittently" while a wheel is turned (DI-238).
The 3RZ-FE instead uses a 3-wire V2 sensor, "4 changes per revolution, 0 to ≥11 V" (BE-39).
What the 1988 cluster has (RM077U BE-63, pdf 1221; BE-73, pdf 1231; BE-24/25):
A reed switch in the speedometer, driven by the cable. "Continuity between B4 and B7 four times per each revolution of the shaft."
B7 = ground. B4 → "TCCS ECU and cruise control computer terminal 7" (88 harness N3-5 G-R, per Monch).
Do they match? Yes, in pulse count and signal form.
Both use Toyota's 4 pulses per speedometer-shaft revolution. [assumed: Toyota's standard 637 rev/km cable, so about 2,548 pulses/km or 4,100 pulses/mile]
The reed switch grounds the ECM's 5 V pull-up, which makes a clean 0/5 V square wave. This is exactly how the 97 T100 M/T fed its ECM (RM507U BE-38, pdf 1832: "continuity A–B four times per revolution").
Connect E12-12 G-O to N3-5 G-R.
Caveats:
(a) If the 88 truck has cruise, its computer shares B4 and may add its own pull-up. Check N3-5 with a meter: it should swing about 0↔5 V with the ECM connected. If it swings to 12 V, unplug the 88 cruise computer.
(b) Contact bounce at very low speed is possible. It hasn't caused trouble on reed-fed Toyota ECMs.
(c) If the R150 drive gear or tire size is off, the ECM's speed reading is off by the same percentage. That only matters for ISC and decel fuel-cut, not for setting codes.
If the signal is missing or wrong: P0500 (DI-236). 2-trip logic. "No vehicle speed sensor signal to ECM":
A/T ECM (yours): P/N switch OFF and vehicle being driven.
M/T ECM: 1,800–3,500 rpm.
OBD-II monitor (OTH021U Ce-51): A/T "vehicle running" is judged from throttle angle, PNP switch and rpm. It runs continuously, detects within 10 s, and lights the MIL after 2 driving cycles.
NSW left open reads as "not P/N". So with no SPD signal, driving will set P0500 and the MIL. The ECM also loses its moving/stopped input for idle and decel control.
A wrong pulse rate (not a missing one) doesn't set P0500. It only skews the ECM's speed reading.

4. Tachometer

98: DIS, 3 coils, waste spark. The igniter has a transistor "TAC" output (RM580U DI-242, P1300 diagram, "To Tachometer"): igniter I2-8 EXT → II3-15 B → meter C11-B7 (EWD p.228).
Each coil fires once per crank revolution, so that's 3 pulses/rev.
The signal is a low-voltage switched pulse with no flyback spike.
88:
The cluster tach input (A-6) is listed as "Ignition coil" (coil negative) for non-TCCS/non-ECT variants (RM077U BE-24, pdf 1182).
A 3VZ-E distributor fires 6 sparks every 2 revs = 3 pulses/rev.
The 3VZ-E harness ran the tach wire from the igniter/coil (−). Monch: "IE2-12 B (igniter tach) → N5-6 L-W". The 93–94 3VZ-E diagram in the project also shows "Igniter → To Tachometer".
Compatibility: the pulse count matches, so no recalibration is needed. The input originally saw coil-negative pulses: 12 V with spikes of a few hundred volts. Now it gets a cleaner low-voltage pulse. Monch reports the 88 tach works on the T100 igniter's tach output. The T100 and 98 5VZ use the same DIS/igniter design.
Check: RM077U BE-26 tolerance is 700 rpm +50/−90; 3,000 ±150; 5,000 ±150; 7,000 ±210. Compare the cluster to the OBD-II rpm reading.
Don't apply 12 V to the tach wire, and don't reverse it. BE-26 caution: that damages the tach's transistors.

5. Check engine light

88: the CEL bulb is in the cluster. One side is fed from IG (ENGINE fuse, cluster C-11). The other side (A-4-1/A-4-2) goes to the ECU, which grounds it (RM077U BE-24/25, pdf 1182–1183).
98: ECM W (E11-3, V). IG ON (lamp on) below 3.0 V; idling (lamp off) 9–14 V (RM580U Terminals of ECM). The 98 lamp is likewise fed from the gauge fuse inside the meter (C11-B4 V, EWD p.229).
Same low-side-switch arrangement → compatible. II1-2 V goes to 88 N5-2 Y.
Test: ground N5-2 with the key ON and the lamp lights.
Expect a bulb check at key ON and the lamp off once running. Self-check flashes happen when TE1 is shorted.
If the 88 bulb has been swapped for an LED, check polarity.

6. Anything else

From the 88 cluster pin table (BE-24/25) and Monch's N3/N5 list, the 3VZ-E harness also fed:

4WD indicator. The transfer switch grounds the bulb (88 BE-31/32). On the 88 it's a chassis/transfer circuit, so keep it from the 88 side.
Back-up lights (N3-2/N3-6): a new pigtail from the R150 switch. Already in the table.
A/C idle-up and clutch. Already in the table.
The warning-light oil switch circuit (A-3-2), on clusters without the gauge package.
Charge warning light: the 98 alternator wiring (IG, L, S) runs through EA1 and the engine-room main wire, not the II joint (EWD p.70). So it isn't in the 98 engine harness at all. Make sure the 88 harness's alternator IG/L/S plug reaches the 5VZ alternator, or move it there. The 98 regulator's L terminal grounds the lamp, same as the 88.
Voltmeter: internal to the cluster. Nothing to do.

Corrections to the project docs

ii-joint-connector-map.md, II3-13 GR-L / II3-14 P-L / II3-20 B-Y:
The V2 speed sensor is "*2 = 3RZ-FE" only (EWD p.228; p.230 parts list "V2 29 (3RZ-FE)"; p.231 "(3RZ-FE) V2").
On a 5VZ donor the meter's speed comes from the ABS ECU (meter C10-A2, GR-L, "*1 = 5VZ-FE"; the RM580U Circuit page has the same note).
So on your harness those II3 cavities are probably empty.
conversion-wiring-table.md, speed row: pulse count is now verified to match (4 per revolution on both sides). What's still unverified is whether the 88 cruise computer's pull-up on the same wire causes trouble.
Temp row: the 98 sender reads about 7–9 °C low on the 88 gauge (calculated above).
Oil row: the T100 sender is the right type (pulse) and fits the port. Its receiver match (25 Ω vs the 88's 44 Ω) is UNVERIFIED.