Knowing what I know now, here's what I would do. (1) assume that the wire from the idiot lights to the back of the alternator (thin red wire) is suffering from failing insulation and that's what's causing the lights to come on.

(2) waste no time on disassembling the under-the-engine harness, it's likely toast anyway and it's a PITA to putz with. The fat red wire is usually OK, the thin ones (black and red) you will leave in but isolated after (3) is done.

(3) Run new wires from the gray firewall connector to both the alternator and the oil pressure sensor. FAQs or archives ought to have info about this one.

Note that when the alternator thin red wire is grounded the idiot lights come on AND the alternator ceases to charge.

Good Luck,

Bob

:>)

Is your splash tray on? Water/dirt may get in alt. and interfere with brush contact.
--
1980 245 Canadian B21A with SU carb and M46 trans

Check the Alt wire that goes to your Idiot light. It goes off the back of your Alt, under to engine to the drivers side fire wall. The insulation was just falling apart on mine. In the FAQ's I think that you will find how to reroute the wire. Of course the Volvo BBers will come to my aid and cover this.

Just a good place to start. If you have replaced the engine harness, ignore this post.

Good Bricking

Check the wiring to the alternator especially where it goes into the loom under the front of the engine. The insulation crumbles and then the wires short out causing the problem you mention. Remove the black plastic wiring protection to check out the wiring.

John