"I want to convert to the hall sender with the rectangular plug used on the '84 because the original round plug unit runs around $290.00 (AC/Delco E1944C), while I can get the '84 rectangular plug hall sender for about $110.00 (Volvo PN 1237031166)...
...
Even though, both of these run with the same ICU (1317295)..."

• I don't know how this impacts your plans, but that "Volvo PN 127031166" is actually Bosch PN 1-237-031-166, which equates to Volvo PN 1346803 — and that 1346803 is the impulse sender for the '85-'87 ICU 1346107 (not your '83-'84 1317295). But if it fits your '83-'84 distributor body, I think it should work with the earlier ICU.

Your 1317295 ICU is listed in my SAVE ("trade" parts book) for the '83-'84 with Automatic Tranny. The matching Impulse Sender is the Bosch 1-237-031-123 (or) Volvo 1276619, which is $93.68 at Tasca Volvo (but maybe that's a round plug???). The '85-'87 1346803 is #105.56 at Tasca.

I think your mechanic is out to lunch about "resistance values". As I understand it, the pulses from the hall switch (any year) are merely interruptions of the nominal 5V control voltage signal from the ICU on the yellow (B) wire. The other 2 wires are 12V input and a ground.

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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.